+ * @author John Rose, JSR 292 EG + * @since 1.7 + */ +public class MethodHandles { + + private MethodHandles() { } // do not instantiate + + private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); + static { MethodHandleImpl.initStatics(); } + // See IMPL_LOOKUP below. + + //// Method handle creation from ordinary methods. + + /** + * Returns a {@link Lookup lookup object} with + * full capabilities to emulate all supported bytecode behaviors of the caller. + * These capabilities include private access to the caller. + * Factory methods on the lookup object can create + * direct method handles + * for any member that the caller has access to via bytecodes, + * including protected and private fields and methods. + * This lookup object is a capability which may be delegated to trusted agents. + * Do not store it in place where untrusted code can access it. + *
+ * This method is caller sensitive, which means that it may return different + * values to different callers. + *
+ * For any given caller class {@code C}, the lookup object returned by this call + * has equivalent capabilities to any lookup object + * supplied by the JVM to the bootstrap method of an + * invokedynamic instruction + * executing in the same caller class {@code C}. + * @return a lookup object for the caller of this method, with private access + */ + @CallerSensitive + public static Lookup lookup() { + return new Lookup(Reflection.getCallerClass()); + } + + /** + * Returns a {@link Lookup lookup object} which is trusted minimally. + * It can only be used to create method handles to + * publicly accessible fields and methods. + *
+ * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class} + * of this lookup object will be {@link java.lang.Object}. + * + *
+ * Discussion: + * The lookup class can be changed to any other class {@code C} using an expression of the form + * {@link Lookup#in publicLookup().in(C.class)}. + * Since all classes have equal access to public names, + * such a change would confer no new access rights. + * A public lookup object is always subject to + * security manager checks. + * Also, it cannot access + * caller sensitive methods. + * @return a lookup object which is trusted minimally + */ + public static Lookup publicLookup() { + return Lookup.PUBLIC_LOOKUP; + } + + /** + * Performs an unchecked "crack" of a + * direct method handle. + * The result is as if the user had obtained a lookup object capable enough + * to crack the target method handle, called + * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} + * on the target to obtain its symbolic reference, and then called + * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} + * to resolve the symbolic reference to a member. + *
+ * If there is a security manager, its {@code checkPermission} method
+ * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
+ * @param
+ * A lookup class which needs to create method handles will call
+ * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
+ * When the {@code Lookup} factory object is created, the identity of the lookup class is
+ * determined, and securely stored in the {@code Lookup} object.
+ * The lookup class (or its delegates) may then use factory methods
+ * on the {@code Lookup} object to create method handles for access-checked members.
+ * This includes all methods, constructors, and fields which are allowed to the lookup class,
+ * even private ones.
+ *
+ *
+ * In cases where the given member is of variable arity (i.e., a method or constructor)
+ * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
+ * In all other cases, the returned method handle will be of fixed arity.
+ *
+ * Discussion:
+ * The equivalence between looked-up method handles and underlying
+ * class members and bytecode behaviors
+ * can break down in a few ways:
+ *
+ * All access checks start from a {@code Lookup} object, which
+ * compares its recorded lookup class against all requests to
+ * create method handles.
+ * A single {@code Lookup} object can be used to create any number
+ * of access-checked method handles, all checked against a single
+ * lookup class.
+ *
+ * A {@code Lookup} object can be shared with other trusted code,
+ * such as a metaobject protocol.
+ * A shared {@code Lookup} object delegates the capability
+ * to create method handles on private members of the lookup class.
+ * Even if privileged code uses the {@code Lookup} object,
+ * the access checking is confined to the privileges of the
+ * original lookup class.
+ *
+ * A lookup can fail, because
+ * the containing class is not accessible to the lookup class, or
+ * because the desired class member is missing, or because the
+ * desired class member is not accessible to the lookup class, or
+ * because the lookup object is not trusted enough to access the member.
+ * In any of these cases, a {@code ReflectiveOperationException} will be
+ * thrown from the attempted lookup. The exact class will be one of
+ * the following:
+ *
+ * In general, the conditions under which a method handle may be
+ * looked up for a method {@code M} are no more restrictive than the conditions
+ * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
+ * Where the JVM would raise exceptions like {@code NoSuchMethodError},
+ * a method handle lookup will generally raise a corresponding
+ * checked exception, such as {@code NoSuchMethodException}.
+ * And the effect of invoking the method handle resulting from the lookup
+ * is exactly equivalent
+ * to executing the compiled, verified, and resolved call to {@code M}.
+ * The same point is true of fields and constructors.
+ *
+ * Discussion:
+ * Access checks only apply to named and reflected methods,
+ * constructors, and fields.
+ * Other method handle creation methods, such as
+ * {@link MethodHandle#asType MethodHandle.asType},
+ * do not require any access checks, and are used
+ * independently of any {@code Lookup} object.
+ *
+ * If the desired member is {@code protected}, the usual JVM rules apply,
+ * including the requirement that the lookup class must be either be in the
+ * same package as the desired member, or must inherit that member.
+ * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
+ * In addition, if the desired member is a non-static field or method
+ * in a different package, the resulting method handle may only be applied
+ * to objects of the lookup class or one of its subclasses.
+ * This requirement is enforced by narrowing the type of the leading
+ * {@code this} parameter from {@code C}
+ * (which will necessarily be a superclass of the lookup class)
+ * to the lookup class itself.
+ *
+ * The JVM imposes a similar requirement on {@code invokespecial} instruction,
+ * that the receiver argument must match both the resolved method and
+ * the current class. Again, this requirement is enforced by narrowing the
+ * type of the leading parameter to the resulting method handle.
+ * (See the Java Virtual Machine Specification, section 4.10.1.9.)
+ *
+ * The JVM represents constructors and static initializer blocks as internal methods
+ * with special names ({@code "
+ * In some cases, access between nested classes is obtained by the Java compiler by creating
+ * an wrapper method to access a private method of another class
+ * in the same top-level declaration.
+ * For example, a nested class {@code C.D}
+ * can access private members within other related classes such as
+ * {@code C}, {@code C.D.E}, or {@code C.B},
+ * but the Java compiler may need to generate wrapper methods in
+ * those related classes. In such cases, a {@code Lookup} object on
+ * {@code C.E} would be unable to those private members.
+ * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
+ * which can transform a lookup on {@code C.E} into one on any of those other
+ * classes, without special elevation of privilege.
+ *
+ * The accesses permitted to a given lookup object may be limited,
+ * according to its set of {@link #lookupModes lookupModes},
+ * to a subset of members normally accessible to the lookup class.
+ * For example, the {@link MethodHandles#publicLookup publicLookup}
+ * method produces a lookup object which is only allowed to access
+ * public members in public classes.
+ * The caller sensitive method {@link MethodHandles#lookup lookup}
+ * produces a lookup object with full capabilities relative to
+ * its caller class, to emulate all supported bytecode behaviors.
+ * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
+ * with fewer access modes than the original lookup object.
+ *
+ *
+ *
+ * Discussion of private access:
+ * We say that a lookup has private access
+ * if its {@linkplain #lookupModes lookup modes}
+ * include the possibility of accessing {@code private} members.
+ * As documented in the relevant methods elsewhere,
+ * only lookups with private access possess the following capabilities:
+ *
+ * Each of these permissions is a consequence of the fact that a lookup object
+ * with private access can be securely traced back to an originating class,
+ * whose bytecode behaviors and Java language access permissions
+ * can be reliably determined and emulated by method handles.
+ *
+ *
+ * If a security manager is present, member lookups are subject to
+ * additional checks.
+ * From one to three calls are made to the security manager.
+ * Any of these calls can refuse access by throwing a
+ * {@link java.lang.SecurityException SecurityException}.
+ * Define {@code smgr} as the security manager,
+ * {@code lookc} as the lookup class of the current lookup object,
+ * {@code refc} as the containing class in which the member
+ * is being sought, and {@code defc} as the class in which the
+ * member is actually defined.
+ * The value {@code lookc} is defined as not present
+ * if the current lookup object does not have
+ * private access.
+ * The calls are made according to the following rules:
+ *
+ * If a method handle for a caller-sensitive method is requested,
+ * the general rules for bytecode behaviors apply,
+ * but they take account of the lookup class in a special way.
+ * The resulting method handle behaves as if it were called
+ * from an instruction contained in the lookup class,
+ * so that the caller-sensitive method detects the lookup class.
+ * (By contrast, the invoker of the method handle is disregarded.)
+ * Thus, in the case of caller-sensitive methods,
+ * different lookup classes may give rise to
+ * differently behaving method handles.
+ *
+ * In cases where the lookup object is
+ * {@link MethodHandles#publicLookup() publicLookup()},
+ * or some other lookup object without
+ * private access,
+ * the lookup class is disregarded.
+ * In such cases, no caller-sensitive method handle can be created,
+ * access is forbidden, and the lookup fails with an
+ * {@code IllegalAccessException}.
+ *
+ * Discussion:
+ * For example, the caller-sensitive method
+ * {@link java.lang.Class#forName(String) Class.forName(x)}
+ * can return varying classes or throw varying exceptions,
+ * depending on the class loader of the class that calls it.
+ * A public lookup of {@code Class.forName} will fail, because
+ * there is no reasonable way to determine its bytecode behavior.
+ *
+ * If an application caches method handles for broad sharing,
+ * it should use {@code publicLookup()} to create them.
+ * If there is a lookup of {@code Class.forName}, it will fail,
+ * and the application must take appropriate action in that case.
+ * It may be that a later lookup, perhaps during the invocation of a
+ * bootstrap method, can incorporate the specific identity
+ * of the caller, making the method accessible.
+ *
+ * The function {@code MethodHandles.lookup} is caller sensitive
+ * so that there can be a secure foundation for lookups.
+ * Nearly all other methods in the JSR 292 API rely on lookup
+ * objects to check access requests.
+ */
+ public static final
+ class Lookup {
+ /** The class on behalf of whom the lookup is being performed. */
+ private final Class lookupClass;
+
+ /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
+ private final int allowedModes;
+
+ /** A single-bit mask representing {@code public} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x01}, happens to be the same as the value of the
+ * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
+ */
+ public static final int PUBLIC = Modifier.PUBLIC;
+
+ /** A single-bit mask representing {@code private} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x02}, happens to be the same as the value of the
+ * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
+ */
+ public static final int PRIVATE = Modifier.PRIVATE;
+
+ /** A single-bit mask representing {@code protected} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x04}, happens to be the same as the value of the
+ * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
+ */
+ public static final int PROTECTED = Modifier.PROTECTED;
+
+ /** A single-bit mask representing {@code package} access (default access),
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value is {@code 0x08}, which does not correspond meaningfully to
+ * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
+ */
+ public static final int PACKAGE = Modifier.STATIC;
+
+ private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
+ private static final int TRUSTED = -1;
+
+ private static int fixmods(int mods) {
+ mods &= (ALL_MODES - PACKAGE);
+ return (mods != 0) ? mods : PACKAGE;
+ }
+
+ /** Tells which class is performing the lookup. It is this class against
+ * which checks are performed for visibility and access permissions.
+ *
+ * The class implies a maximum level of access permission,
+ * but the permissions may be additionally limited by the bitmask
+ * {@link #lookupModes lookupModes}, which controls whether non-public members
+ * can be accessed.
+ * @return the lookup class, on behalf of which this lookup object finds members
+ */
+ public Class lookupClass() {
+ return lookupClass;
+ }
+
+ // This is just for calling out to MethodHandleImpl.
+ private Class lookupClassOrNull() {
+ return (allowedModes == TRUSTED) ? null : lookupClass;
+ }
+
+ /** Tells which access-protection classes of members this lookup object can produce.
+ * The result is a bit-mask of the bits
+ * {@linkplain #PUBLIC PUBLIC (0x01)},
+ * {@linkplain #PRIVATE PRIVATE (0x02)},
+ * {@linkplain #PROTECTED PROTECTED (0x04)},
+ * and {@linkplain #PACKAGE PACKAGE (0x08)}.
+ *
+ * A freshly-created lookup object
+ * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
+ * has all possible bits set, since the caller class can access all its own members.
+ * A lookup object on a new lookup class
+ * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
+ * may have some mode bits set to zero.
+ * The purpose of this is to restrict access via the new lookup object,
+ * so that it can access only names which can be reached by the original
+ * lookup object, and also by the new lookup class.
+ * @return the lookup modes, which limit the kinds of access performed by this lookup object
+ */
+ public int lookupModes() {
+ return allowedModes & ALL_MODES;
+ }
+
+ /** Embody the current class (the lookupClass) as a lookup class
+ * for method handle creation.
+ * Must be called by from a method in this package,
+ * which in turn is called by a method not in this package.
+ */
+ Lookup(Class lookupClass) {
+ this(lookupClass, ALL_MODES);
+ // make sure we haven't accidentally picked up a privileged class:
+ checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
+ }
+
+ private Lookup(Class lookupClass, int allowedModes) {
+ this.lookupClass = lookupClass;
+ this.allowedModes = allowedModes;
+ }
+
+ /**
+ * Creates a lookup on the specified new lookup class.
+ * The resulting object will report the specified
+ * class as its own {@link #lookupClass lookupClass}.
+ *
+ * However, the resulting {@code Lookup} object is guaranteed
+ * to have no more access capabilities than the original.
+ * In particular, access capabilities can be lost as follows:
+ * (It may seem strange that protected access should be
+ * stronger than private access. Viewed independently from
+ * package access, protected access is the first to be lost,
+ * because it requires a direct subclass relationship between
+ * caller and callee.)
+ * @see #in
+ */
+ @Override
+ public String toString() {
+ String cname = lookupClass.getName();
+ switch (allowedModes) {
+ case 0: // no privileges
+ return cname + "/noaccess";
+ case PUBLIC:
+ return cname + "/public";
+ case PUBLIC|PACKAGE:
+ return cname + "/package";
+ case ALL_MODES & ~PROTECTED:
+ return cname + "/private";
+ case ALL_MODES:
+ return cname;
+ case TRUSTED:
+ return "/trusted"; // internal only; not exported
+ default: // Should not happen, but it's a bitfield...
+ cname = cname + "/" + Integer.toHexString(allowedModes);
+ assert(false) : cname;
+ return cname;
+ }
+ }
+
+ /**
+ * Produces a method handle for a static method.
+ * The type of the method handle will be that of the method.
+ * (Since static methods do not take receivers, there is no
+ * additional receiver argument inserted into the method handle type,
+ * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
+ * The method and all its argument types must be accessible to the lookup object.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If the returned method handle is invoked, the method's class will
+ * be initialized, if it has not already been initialized.
+ * Example:
+ *
+ * When called, the handle will treat the first argument as a receiver
+ * and dispatch on the receiver's type to determine which method
+ * implementation to enter.
+ * (The dispatching action is identical with that performed by an
+ * {@code invokevirtual} or {@code invokeinterface} instruction.)
+ *
+ * The first argument will be of type {@code refc} if the lookup
+ * class has full privileges to access the member. Otherwise
+ * the member must be {@code protected} and the first argument
+ * will be restricted in type to the lookup class.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * Because of the general equivalence between {@code invokevirtual}
+ * instructions and method handles produced by {@code findVirtual},
+ * if the class is {@code MethodHandle} and the name string is
+ * {@code invokeExact} or {@code invoke}, the resulting
+ * method handle is equivalent to one produced by
+ * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
+ * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
+ * with the same {@code type} argument.
+ *
+ * Example:
+ *
+ * The requested type must have a return type of {@code void}.
+ * (This is consistent with the JVM's treatment of constructor type descriptors.)
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If the returned method handle is invoked, the constructor's class will
+ * be initialized, if it has not already been initialized.
+ * Example:
+ *
+ * Before method resolution,
+ * if the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have
+ * private access
+ * privileges, the access fails.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * (Note: JVM internal methods named {@code " Example:
+ *
+ * If the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
+ return getDirectField(REF_getStatic, refc, field);
+ }
+
+ /**
+ * Produces a method handle giving write access to a static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
+ return getDirectField(REF_putStatic, refc, field);
+ }
+
+ /**
+ * Produces an early-bound method handle for a non-static method.
+ * The receiver must have a supertype {@code defc} in which a method
+ * of the given name and type is accessible to the lookup class.
+ * The method and all its argument types must be accessible to the lookup object.
+ * The type of the method handle will be that of the method,
+ * without any insertion of an additional receiver parameter.
+ * The given receiver will be bound into the method handle,
+ * so that every call to the method handle will invoke the
+ * requested method on the given receiver.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set
+ * and the trailing array argument is not the only argument.
+ * (If the trailing array argument is the only argument,
+ * the given receiver value will be bound to it.)
+ *
+ * This is equivalent to the following code:
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If m is static, and
+ * if the returned method handle is invoked, the method's class will
+ * be initialized, if it has not already been initialized.
+ * @param m the reflected method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflect(Method m) throws IllegalAccessException {
+ if (m.getDeclaringClass() == MethodHandle.class) {
+ MethodHandle mh = unreflectForMH(m);
+ if (mh != null) return mh;
+ }
+ MemberName method = new MemberName(m);
+ byte refKind = method.getReferenceKind();
+ if (refKind == REF_invokeSpecial)
+ refKind = REF_invokeVirtual;
+ assert(method.isMethod());
+ Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
+ return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
+ }
+ private MethodHandle unreflectForMH(Method m) {
+ // these names require special lookups because they throw UnsupportedOperationException
+ if (MemberName.isMethodHandleInvokeName(m.getName()))
+ return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
+ return null;
+ }
+
+ /**
+ * Produces a method handle for a reflected method.
+ * It will bypass checks for overriding methods on the receiver,
+ * as if called from an {@code invokespecial}
+ * instruction from within the explicitly specified {@code specialCaller}.
+ * The type of the method handle will be that of the method,
+ * with a suitably restricted receiver type prepended.
+ * (The receiver type will be {@code specialCaller} or a subtype.)
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class,
+ * as if {@code invokespecial} instruction were being linked.
+ *
+ * Before method resolution,
+ * if the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have
+ * private access
+ * privileges, the access fails.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param m the reflected method
+ * @param specialCaller the class nominally calling the method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle unreflectSpecial(Method m, Class specialCaller) throws IllegalAccessException {
+ checkSpecialCaller(specialCaller);
+ Lookup specialLookup = this.in(specialCaller);
+ MemberName method = new MemberName(m, true);
+ assert(method.isMethod());
+ // ignore m.isAccessible: this is a new kind of access
+ return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
+ }
+
+ /**
+ * Produces a method handle for a reflected constructor.
+ * The type of the method handle will be that of the constructor,
+ * with the return type changed to the declaring class.
+ * The method handle will perform a {@code newInstance} operation,
+ * creating a new instance of the constructor's class on the
+ * arguments passed to the method handle.
+ *
+ * If the constructor's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If the returned method handle is invoked, the constructor's class will
+ * be initialized, if it has not already been initialized.
+ * @param c the reflected constructor
+ * @return a method handle which can invoke the reflected constructor
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
+ MemberName ctor = new MemberName(c);
+ assert(ctor.isConstructor());
+ Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
+ return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
+ }
+
+ /**
+ * Produces a method handle giving read access to a reflected field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * If the field is static, the method handle will take no arguments.
+ * Otherwise, its single argument will be the instance containing
+ * the field.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the field is static, and
+ * if the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param f the reflected field
+ * @return a method handle which can load values from the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
+ return unreflectField(f, false);
+ }
+ private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
+ MemberName field = new MemberName(f, isSetter);
+ assert(isSetter
+ ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
+ : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
+ Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
+ return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
+ }
+
+ /**
+ * Produces a method handle giving write access to a reflected field.
+ * The type of the method handle will have a void return type.
+ * If the field is static, the method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Otherwise, the two arguments will be the instance containing
+ * the field, and the value to be stored.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the field is static, and
+ * if the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param f the reflected field
+ * @return a method handle which can store values into the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
+ return unreflectField(f, true);
+ }
+
+ /**
+ * Cracks a direct method handle
+ * created by this lookup object or a similar one.
+ * Security and access checks are performed to ensure that this lookup object
+ * is capable of reproducing the target method handle.
+ * This means that the cracking may fail if target is a direct method handle
+ * but was created by an unrelated lookup object.
+ * This can happen if the method handle is caller sensitive
+ * and was created by a lookup object for a different class.
+ * @param target a direct method handle to crack into symbolic reference components
+ * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
+ * @exception NullPointerException if the target is {@code null}
+ * @see MethodHandleInfo
+ * @since 1.8
+ */
+ public MethodHandleInfo revealDirect(MethodHandle target) {
+ MemberName member = target.internalMemberName();
+ if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
+ throw newIllegalArgumentException("not a direct method handle");
+ Class defc = member.getDeclaringClass();
+ byte refKind = member.getReferenceKind();
+ assert(MethodHandleNatives.refKindIsValid(refKind));
+ if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
+ // Devirtualized method invocation is usually formally virtual.
+ // To avoid creating extra MemberName objects for this common case,
+ // we encode this extra degree of freedom using MH.isInvokeSpecial.
+ refKind = REF_invokeVirtual;
+ if (refKind == REF_invokeVirtual && defc.isInterface())
+ // Symbolic reference is through interface but resolves to Object method (toString, etc.)
+ refKind = REF_invokeInterface;
+ // Check SM permissions and member access before cracking.
+ try {
+ checkAccess(refKind, defc, member);
+ checkSecurityManager(defc, member);
+ } catch (IllegalAccessException ex) {
+ throw new IllegalArgumentException(ex);
+ }
+ if (allowedModes != TRUSTED && member.isCallerSensitive()) {
+ Class callerClass = target.internalCallerClass();
+ if (!hasPrivateAccess() || callerClass != lookupClass())
+ throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
+ }
+ // Produce the handle to the results.
+ return new InfoFromMemberName(this, member, refKind);
+ }
+
+ /// Helper methods, all package-private.
+
+ MemberName resolveOrFail(byte refKind, Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ name.getClass(); // NPE
+ type.getClass(); // NPE
+ return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
+ NoSuchFieldException.class);
+ }
+
+ MemberName resolveOrFail(byte refKind, Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ name.getClass(); // NPE
+ type.getClass(); // NPE
+ checkMethodName(refKind, name); // NPE check on name
+ return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
+ NoSuchMethodException.class);
+ }
+
+ MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
+ checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
+ member.getName().getClass(); // NPE
+ member.getType().getClass(); // NPE
+ return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
+ ReflectiveOperationException.class);
+ }
+
+ void checkSymbolicClass(Class refc) throws IllegalAccessException {
+ refc.getClass(); // NPE
+ Class caller = lookupClassOrNull();
+ if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
+ throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
+ }
+
+ /** Check name for an illegal leading "<" character. */
+ void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
+ if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
+ throw new NoSuchMethodException("illegal method name: "+name);
+ }
+
+
+ /**
+ * Find my trustable caller class if m is a caller sensitive method.
+ * If this lookup object has private access, then the caller class is the lookupClass.
+ * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
+ */
+ Class findBoundCallerClass(MemberName m) throws IllegalAccessException {
+ Class callerClass = null;
+ if (MethodHandleNatives.isCallerSensitive(m)) {
+ // Only lookups with private access are allowed to resolve caller-sensitive methods
+ if (hasPrivateAccess()) {
+ callerClass = lookupClass;
+ } else {
+ throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
+ }
+ }
+ return callerClass;
+ }
+
+ private boolean hasPrivateAccess() {
+ return (allowedModes & PRIVATE) != 0;
+ }
+
+ /**
+ * Perform necessary access checks.
+ * Determines a trustable caller class to compare with refc, the symbolic reference class.
+ * If this lookup object has private access, then the caller class is the lookupClass.
+ */
+ void checkSecurityManager(Class refc, MemberName m) {
+ SecurityManager smgr = System.getSecurityManager();
+ if (smgr == null) return;
+ if (allowedModes == TRUSTED) return;
+
+ // Step 1:
+ boolean fullPowerLookup = hasPrivateAccess();
+ if (!fullPowerLookup ||
+ !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
+ ReflectUtil.checkPackageAccess(refc);
+ }
+
+ // Step 2:
+ if (m.isPublic()) return;
+ if (!fullPowerLookup) {
+ smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
+ }
+
+ // Step 3:
+ Class defc = m.getDeclaringClass();
+ if (!fullPowerLookup && defc != refc) {
+ ReflectUtil.checkPackageAccess(defc);
+ }
+ }
+
+ void checkMethod(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
+ boolean wantStatic = (refKind == REF_invokeStatic);
+ String message;
+ if (m.isConstructor())
+ message = "expected a method, not a constructor";
+ else if (!m.isMethod())
+ message = "expected a method";
+ else if (wantStatic != m.isStatic())
+ message = wantStatic ? "expected a static method" : "expected a non-static method";
+ else
+ { checkAccess(refKind, refc, m); return; }
+ throw m.makeAccessException(message, this);
+ }
+
+ void checkField(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
+ boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
+ String message;
+ if (wantStatic != m.isStatic())
+ message = wantStatic ? "expected a static field" : "expected a non-static field";
+ else
+ { checkAccess(refKind, refc, m); return; }
+ throw m.makeAccessException(message, this);
+ }
+
+ /** Check public/protected/private bits on the symbolic reference class and its member. */
+ void checkAccess(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
+ assert(m.referenceKindIsConsistentWith(refKind) &&
+ MethodHandleNatives.refKindIsValid(refKind) &&
+ (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
+ int allowedModes = this.allowedModes;
+ if (allowedModes == TRUSTED) return;
+ int mods = m.getModifiers();
+ if (Modifier.isProtected(mods) &&
+ refKind == REF_invokeVirtual &&
+ m.getDeclaringClass() == Object.class &&
+ m.getName().equals("clone") &&
+ refc.isArray()) {
+ // The JVM does this hack also.
+ // (See ClassVerifier::verify_invoke_instructions
+ // and LinkResolver::check_method_accessability.)
+ // Because the JVM does not allow separate methods on array types,
+ // there is no separate method for int[].clone.
+ // All arrays simply inherit Object.clone.
+ // But for access checking logic, we make Object.clone
+ // (normally protected) appear to be public.
+ // Later on, when the DirectMethodHandle is created,
+ // its leading argument will be restricted to the
+ // requested array type.
+ // N.B. The return type is not adjusted, because
+ // that is *not* the bytecode behavior.
+ mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
+ }
+ if (Modifier.isFinal(mods) &&
+ MethodHandleNatives.refKindIsSetter(refKind))
+ throw m.makeAccessException("unexpected set of a final field", this);
+ if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
+ return; // common case
+ int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
+ if ((requestedModes & allowedModes) != 0) {
+ if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
+ mods, lookupClass(), allowedModes))
+ return;
+ } else {
+ // Protected members can also be checked as if they were package-private.
+ if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
+ && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
+ return;
+ }
+ throw m.makeAccessException(accessFailedMessage(refc, m), this);
+ }
+
+ String accessFailedMessage(Class refc, MemberName m) {
+ Class defc = m.getDeclaringClass();
+ int mods = m.getModifiers();
+ // check the class first:
+ boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
+ (defc == refc ||
+ Modifier.isPublic(refc.getModifiers())));
+ if (!classOK && (allowedModes & PACKAGE) != 0) {
+ classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
+ (defc == refc ||
+ VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
+ }
+ if (!classOK)
+ return "class is not public";
+ if (Modifier.isPublic(mods))
+ return "access to public member failed"; // (how?)
+ if (Modifier.isPrivate(mods))
+ return "member is private";
+ if (Modifier.isProtected(mods))
+ return "member is protected";
+ return "member is private to package";
+ }
+
+ private static final boolean ALLOW_NESTMATE_ACCESS = false;
+
+ private void checkSpecialCaller(Class specialCaller) throws IllegalAccessException {
+ int allowedModes = this.allowedModes;
+ if (allowedModes == TRUSTED) return;
+ if (!hasPrivateAccess()
+ || (specialCaller != lookupClass()
+ && !(ALLOW_NESTMATE_ACCESS &&
+ VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
+ throw new MemberName(specialCaller).
+ makeAccessException("no private access for invokespecial", this);
+ }
+
+ private boolean restrictProtectedReceiver(MemberName method) {
+ // The accessing class only has the right to use a protected member
+ // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
+ if (!method.isProtected() || method.isStatic()
+ || allowedModes == TRUSTED
+ || method.getDeclaringClass() == lookupClass()
+ || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
+ || (ALLOW_NESTMATE_ACCESS &&
+ VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
+ return false;
+ return true;
+ }
+ private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class caller) throws IllegalAccessException {
+ assert(!method.isStatic());
+ // receiver type of mh is too wide; narrow to caller
+ if (!method.getDeclaringClass().isAssignableFrom(caller)) {
+ throw method.makeAccessException("caller class must be a subclass below the method", caller);
+ }
+ MethodType rawType = mh.type();
+ if (rawType.parameterType(0) == caller) return mh;
+ MethodType narrowType = rawType.changeParameterType(0, caller);
+ return mh.viewAsType(narrowType);
+ }
+
+ /** Check access and get the requested method. */
+ private MethodHandle getDirectMethod(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
+ final boolean doRestrict = true;
+ final boolean checkSecurity = true;
+ return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
+ }
+ /** Check access and get the requested method, eliding receiver narrowing rules. */
+ private MethodHandle getDirectMethodNoRestrict(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
+ final boolean doRestrict = false;
+ final boolean checkSecurity = true;
+ return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
+ }
+ /** Check access and get the requested method, eliding security manager checks. */
+ private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
+ final boolean doRestrict = true;
+ final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
+ return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
+ }
+ /** Common code for all methods; do not call directly except from immediately above. */
+ private MethodHandle getDirectMethodCommon(byte refKind, Class refc, MemberName method,
+ boolean checkSecurity,
+ boolean doRestrict, Class callerClass) throws IllegalAccessException {
+ checkMethod(refKind, refc, method);
+ // Optionally check with the security manager; this isn't needed for unreflect* calls.
+ if (checkSecurity)
+ checkSecurityManager(refc, method);
+ assert(!method.isMethodHandleInvoke());
+
+ Class refcAsSuper;
+ if (refKind == REF_invokeSpecial &&
+ refc != lookupClass() &&
+ !refc.isInterface() &&
+ refc != (refcAsSuper = lookupClass().getSuperclass()) &&
+ refc.isAssignableFrom(lookupClass())) {
+ assert(!method.getName().equals("
+ * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
+ * the indicated {@code type}.
+ * That is, if the target is exactly of the given {@code type}, it will behave
+ * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
+ * is used to convert the target to the required {@code type}.
+ *
+ * The type of the returned invoker will not be the given {@code type}, but rather
+ * will have all parameters except the first {@code leadingArgCount}
+ * replaced by a single array of type {@code Object[]}, which will be
+ * the final parameter.
+ *
+ * Before invoking its target, the invoker will spread the final array, apply
+ * reference casts as necessary, and unbox and widen primitive arguments.
+ * If, when the invoker is called, the supplied array argument does
+ * not have the correct number of elements, the invoker will throw
+ * an {@link IllegalArgumentException} instead of invoking the target.
+ *
+ * This method is equivalent to the following code (though it may be more efficient):
+ *
+ * This method is equivalent to the following code (though it may be more efficient):
+ * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
+ *
+ *
+ * Discussion:
+ * Invoker method handles can be useful when working with variable method handles
+ * of unknown types.
+ * For example, to emulate an {@code invokeExact} call to a variable method
+ * handle {@code M}, extract its type {@code T},
+ * look up the invoker method {@code X} for {@code T},
+ * and call the invoker method, as {@code X.invoke(T, A...)}.
+ * (It would not work to call {@code X.invokeExact}, since the type {@code T}
+ * is unknown.)
+ * If spreading, collecting, or other argument transformations are required,
+ * they can be applied once to the invoker {@code X} and reused on many {@code M}
+ * method handle values, as long as they are compatible with the type of {@code X}.
+ *
+ * (Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * on the declared {@code invokeExact} or {@code invoke} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)
+ *
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle of the given type
+ * @throws IllegalArgumentException if the resulting method handle's type would have
+ * too many parameters
+ */
+ static public
+ MethodHandle exactInvoker(MethodType type) {
+ return type.invokers().exactInvoker();
+ }
+
+ /**
+ * Produces a special invoker method handle which can be used to
+ * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ *
+ * Before invoking its target, if the target differs from the expected type,
+ * the invoker will apply reference casts as
+ * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
+ * Similarly, the return value will be converted as necessary.
+ * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
+ * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
+ *
+ * This method is equivalent to the following code (though it may be more efficient):
+ * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
+ *
+ * Discussion:
+ * A {@linkplain MethodType#genericMethodType general method type} is one which
+ * mentions only {@code Object} arguments and return values.
+ * An invoker for such a type is capable of calling any method handle
+ * of the same arity as the general type.
+ *
+ * (Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * on the declared {@code invokeExact} or {@code invoke} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)
+ *
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle convertible to the given type
+ * @throws IllegalArgumentException if the resulting method handle's type would have
+ * too many parameters
+ */
+ static public
+ MethodHandle invoker(MethodType type) {
+ return type.invokers().generalInvoker();
+ }
+
+ static /*non-public*/
+ MethodHandle basicInvoker(MethodType type) {
+ return type.form().basicInvoker();
+ }
+
+ /// method handle modification (creation from other method handles)
+
+ /**
+ * Produces a method handle which adapts the type of the
+ * given method handle to a new type by pairwise argument and return type conversion.
+ * The original type and new type must have the same number of arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ *
+ * If the original type and new type are equal, returns target.
+ *
+ * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
+ * and some additional conversions are also applied if those conversions fail.
+ * Given types T0, T1, one of the following conversions is applied
+ * if possible, before or instead of any conversions done by {@code asType}:
+ *
+ * The given array controls the reordering.
+ * Call {@code #I} the number of incoming parameters (the value
+ * {@code newType.parameterCount()}, and call {@code #O} the number
+ * of outgoing parameters (the value {@code target.type().parameterCount()}).
+ * Then the length of the reordering array must be {@code #O},
+ * and each element must be a non-negative number less than {@code #I}.
+ * For every {@code N} less than {@code #O}, the {@code N}-th
+ * outgoing argument will be taken from the {@code I}-th incoming
+ * argument, where {@code I} is {@code reorder[N]}.
+ *
+ * No argument or return value conversions are applied.
+ * The type of each incoming argument, as determined by {@code newType},
+ * must be identical to the type of the corresponding outgoing parameter
+ * or parameters in the target method handle.
+ * The return type of {@code newType} must be identical to the return
+ * type of the original target.
+ *
+ * The reordering array need not specify an actual permutation.
+ * An incoming argument will be duplicated if its index appears
+ * more than once in the array, and an incoming argument will be dropped
+ * if its index does not appear in the array.
+ * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
+ * incoming arguments which are not mentioned in the reordering array
+ * are may be any type, as determined only by {@code newType}.
+ *
+ * Before the method handle is returned, the passed-in value is converted to the requested type.
+ * If the requested type is primitive, widening primitive conversions are attempted,
+ * else reference conversions are attempted.
+ * The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
+ * @param type the return type of the desired method handle
+ * @param value the value to return
+ * @return a method handle of the given return type and no arguments, which always returns the given value
+ * @throws NullPointerException if the {@code type} argument is null
+ * @throws ClassCastException if the value cannot be converted to the required return type
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle constant(Class type, Object value) {
+ if (type.isPrimitive()) {
+ if (type == void.class)
+ throw newIllegalArgumentException("void type");
+ Wrapper w = Wrapper.forPrimitiveType(type);
+ return insertArguments(identity(type), 0, w.convert(value, type));
+ } else {
+ return identity(type).bindTo(type.cast(value));
+ }
+ }
+
+ /**
+ * Produces a method handle which returns its sole argument when invoked.
+ * @param type the type of the sole parameter and return value of the desired method handle
+ * @return a unary method handle which accepts and returns the given type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle identity(Class type) {
+ if (type == void.class)
+ throw newIllegalArgumentException("void type");
+ else if (type == Object.class)
+ return ValueConversions.identity();
+ else if (type.isPrimitive())
+ return ValueConversions.identity(Wrapper.forPrimitiveType(type));
+ else
+ return MethodHandleImpl.makeReferenceIdentity(type);
+ }
+
+ /**
+ * Provides a target method handle with one or more bound arguments
+ * in advance of the method handle's invocation.
+ * The formal parameters to the target corresponding to the bound
+ * arguments are called bound parameters.
+ * Returns a new method handle which saves away the bound arguments.
+ * When it is invoked, it receives arguments for any non-bound parameters,
+ * binds the saved arguments to their corresponding parameters,
+ * and calls the original target.
+ *
+ * The type of the new method handle will drop the types for the bound
+ * parameters from the original target type, since the new method handle
+ * will no longer require those arguments to be supplied by its callers.
+ *
+ * Each given argument object must match the corresponding bound parameter type.
+ * If a bound parameter type is a primitive, the argument object
+ * must be a wrapper, and will be unboxed to produce the primitive value.
+ *
+ * The {@code pos} argument selects which parameters are to be bound.
+ * It may range between zero and N-L (inclusively),
+ * where N is the arity of the target method handle
+ * and L is the length of the values array.
+ * @param target the method handle to invoke after the argument is inserted
+ * @param pos where to insert the argument (zero for the first)
+ * @param values the series of arguments to insert
+ * @return a method handle which inserts an additional argument,
+ * before calling the original method handle
+ * @throws NullPointerException if the target or the {@code values} array is null
+ * @see MethodHandle#bindTo
+ */
+ public static
+ MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
+ int insCount = values.length;
+ MethodType oldType = target.type();
+ int outargs = oldType.parameterCount();
+ int inargs = outargs - insCount;
+ if (inargs < 0)
+ throw newIllegalArgumentException("too many values to insert");
+ if (pos < 0 || pos > inargs)
+ throw newIllegalArgumentException("no argument type to append");
+ MethodHandle result = target;
+ for (int i = 0; i < insCount; i++) {
+ Object value = values[i];
+ Class ptype = oldType.parameterType(pos+i);
+ if (ptype.isPrimitive()) {
+ char btype = 'I';
+ Wrapper w = Wrapper.forPrimitiveType(ptype);
+ switch (w) {
+ case LONG: btype = 'J'; break;
+ case FLOAT: btype = 'F'; break;
+ case DOUBLE: btype = 'D'; break;
+ }
+ // perform unboxing and/or primitive conversion
+ value = w.convert(value, ptype);
+ result = result.bindArgument(pos, btype, value);
+ continue;
+ }
+ value = ptype.cast(value); // throw CCE if needed
+ if (pos == 0) {
+ result = result.bindReceiver(value);
+ } else {
+ result = result.bindArgument(pos, 'L', value);
+ }
+ }
+ return result;
+ }
+
+ /**
+ * Produces a method handle which will discard some dummy arguments
+ * before calling some other specified target method handle.
+ * The type of the new method handle will be the same as the target's type,
+ * except it will also include the dummy argument types,
+ * at some given position.
+ *
+ * The {@code pos} argument may range between zero and N,
+ * where N is the arity of the target.
+ * If {@code pos} is zero, the dummy arguments will precede
+ * the target's real arguments; if {@code pos} is N
+ * they will come after.
+ *
+ * Example:
+ *
+ * This method is also equivalent to the following code:
+ *
+ * The {@code pos} argument may range between zero and N,
+ * where N is the arity of the target.
+ * If {@code pos} is zero, the dummy arguments will precede
+ * the target's real arguments; if {@code pos} is N
+ * they will come after.
+ *
+ * Example:
+ *
+ * This method is also equivalent to the following code:
+ *
+ * The pre-processing is performed by one or more method handles,
+ * specified in the elements of the {@code filters} array.
+ * The first element of the filter array corresponds to the {@code pos}
+ * argument of the target, and so on in sequence.
+ *
+ * Null arguments in the array are treated as identity functions,
+ * and the corresponding arguments left unchanged.
+ * (If there are no non-null elements in the array, the original target is returned.)
+ * Each filter is applied to the corresponding argument of the adapter.
+ *
+ * If a filter {@code F} applies to the {@code N}th argument of
+ * the target, then {@code F} must be a method handle which
+ * takes exactly one argument. The type of {@code F}'s sole argument
+ * replaces the corresponding argument type of the target
+ * in the resulting adapted method handle.
+ * The return type of {@code F} must be identical to the corresponding
+ * parameter type of the target.
+ *
+ * It is an error if there are elements of {@code filters}
+ * (null or not)
+ * which do not correspond to argument positions in the target.
+ * Example:
+ * Here is pseudocode for the resulting adapter:
+ *
+ * If the filter returns a value, the target must accept that value as
+ * its argument in position {@code pos}, preceded and/or followed by
+ * any arguments not passed to the filter.
+ * If the filter returns void, the target must accept all arguments
+ * not passed to the filter.
+ * No arguments are reordered, and a result returned from the filter
+ * replaces (in order) the whole subsequence of arguments originally
+ * passed to the adapter.
+ *
+ * The argument types (if any) of the filter
+ * replace zero or one argument types of the target, at position {@code pos},
+ * in the resulting adapted method handle.
+ * The return type of the filter (if any) must be identical to the
+ * argument type of the target at position {@code pos}, and that target argument
+ * is supplied by the return value of the filter.
+ *
+ * In all cases, {@code pos} must be greater than or equal to zero, and
+ * {@code pos} must also be less than or equal to the target's arity.
+ * Example:
+ * Here is pseudocode for the resulting adapter:
+ *
+ * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
+ * one which first "folds" the affected arguments, and then drops them, in separate
+ * steps as follows:
+ *
+ * If the target returns a value, the filter must accept that value as
+ * its only argument.
+ * If the target returns void, the filter must accept no arguments.
+ *
+ * The return type of the filter
+ * replaces the return type of the target
+ * in the resulting adapted method handle.
+ * The argument type of the filter (if any) must be identical to the
+ * return type of the target.
+ * Example:
+ * Here is pseudocode for the resulting adapter:
+ *
+ * The pre-processing is performed by {@code combiner}, a second method handle.
+ * Of the arguments passed to the adapter, the first {@code N} arguments
+ * are copied to the combiner, which is then called.
+ * (Here, {@code N} is defined as the parameter count of the combiner.)
+ * After this, control passes to the target, with any result
+ * from the combiner inserted before the original {@code N} incoming
+ * arguments.
+ *
+ * If the combiner returns a value, the first parameter type of the target
+ * must be identical with the return type of the combiner, and the next
+ * {@code N} parameter types of the target must exactly match the parameters
+ * of the combiner.
+ *
+ * If the combiner has a void return, no result will be inserted,
+ * and the first {@code N} parameter types of the target
+ * must exactly match the parameters of the combiner.
+ *
+ * The resulting adapter is the same type as the target, except that the
+ * first parameter type is dropped,
+ * if it corresponds to the result of the combiner.
+ *
+ * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
+ * that either the combiner or the target does not wish to receive.
+ * If some of the incoming arguments are destined only for the combiner,
+ * consider using {@link MethodHandle#asCollector asCollector} instead, since those
+ * arguments will not need to be live on the stack on entry to the
+ * target.)
+ * Example:
+ * Here is pseudocode for the resulting adapter:
+ * Here is pseudocode for the resulting adapter:
+ *
+ * The target and handler must have the same corresponding
+ * argument and return types, except that handler may omit trailing arguments
+ * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
+ * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
+ * Here is pseudocode for the resulting adapter:
+ *
+ * The target and handler must return the same type, even if the handler
+ * always throws. (This might happen, for instance, because the handler
+ * is simulating a {@code finally} clause).
+ * To create such a throwing handler, compose the handler creation logic
+ * with {@link #throwException throwException},
+ * in order to create a method handle of the correct return type.
+ * @param target method handle to call
+ * @param exType the type of exception which the handler will catch
+ * @param handler method handle to call if a matching exception is thrown
+ * @return method handle which incorporates the specified try/catch logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code handler} does not accept
+ * the given exception type, or if the method handle types do
+ * not match in their return types and their
+ * corresponding parameters
+ */
+ public static
+ MethodHandle catchException(MethodHandle target,
+ Class exType,
+ MethodHandle handler) {
+ MethodType ttype = target.type();
+ MethodType htype = handler.type();
+ if (htype.parameterCount() < 1 ||
+ !htype.parameterType(0).isAssignableFrom(exType))
+ throw newIllegalArgumentException("handler does not accept exception type "+exType);
+ if (htype.returnType() != ttype.returnType())
+ throw misMatchedTypes("target and handler return types", ttype, htype);
+ ListLookup Factory Methods
+ * The factory methods on a {@code Lookup} object correspond to all major
+ * use cases for methods, constructors, and fields.
+ * Each method handle created by a factory method is the functional
+ * equivalent of a particular bytecode behavior.
+ * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
+ * Here is a summary of the correspondence between these factory methods and
+ * the behavior the resulting method handles:
+ *
+ *
+ *
+ * Access checking
+ * Access checks are applied in the factory methods of {@code Lookup},
+ * when a method handle is created.
+ * This is a key difference from the Core Reflection API, since
+ * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * performs access checking against every caller, on every call.
+ *
+ *
+ *
+ *
+ * Security manager interactions
+ * Although bytecode instructions can only refer to classes in
+ * a related class loader, this API can search for methods in any
+ * class, as long as a reference to its {@code Class} object is
+ * available. Such cross-loader references are also possible with the
+ * Core Reflection API, and are impossible to bytecode instructions
+ * such as {@code invokestatic} or {@code getfield}.
+ * There is a {@linkplain java.lang.SecurityManager security manager API}
+ * to allow applications to check such cross-loader references.
+ * These checks apply to both the {@code MethodHandles.Lookup} API
+ * and the Core Reflection API
+ * (as found on {@link java.lang.Class Class}).
+ *
+ *
+ * Security checks are performed after other access checks have passed.
+ * Therefore, the above rules presuppose a member that is public,
+ * or else that is being accessed from a lookup class that has
+ * rights to access the member.
+ *
+ * Caller sensitive methods
+ * A small number of Java methods have a special property called caller sensitivity.
+ * A caller-sensitive method can behave differently depending on the
+ * identity of its immediate caller.
+ *
+ *
+ *
+ * @param requestedLookupClass the desired lookup class for the new lookup object
+ * @return a lookup object which reports the desired lookup class
+ * @throws NullPointerException if the argument is null
+ */
+ public Lookup in(Class requestedLookupClass) {
+ requestedLookupClass.getClass(); // null check
+ if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
+ return new Lookup(requestedLookupClass, ALL_MODES);
+ if (requestedLookupClass == this.lookupClass)
+ return this; // keep same capabilities
+ int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
+ if ((newModes & PACKAGE) != 0
+ && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~(PACKAGE|PRIVATE);
+ }
+ // Allow nestmate lookups to be created without special privilege:
+ if ((newModes & PRIVATE) != 0
+ && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~PRIVATE;
+ }
+ if ((newModes & PUBLIC) != 0
+ && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
+ // The requested class it not accessible from the lookup class.
+ // No permissions.
+ newModes = 0;
+ }
+ checkUnprivilegedlookupClass(requestedLookupClass, newModes);
+ return new Lookup(requestedLookupClass, newModes);
+ }
+
+ // Make sure outer class is initialized first.
+ static { IMPL_NAMES.getClass(); }
+
+ /** Version of lookup which is trusted minimally.
+ * It can only be used to create method handles to
+ * publicly accessible members.
+ */
+ static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
+
+ /** Package-private version of lookup which is trusted. */
+ static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
+
+ private static void checkUnprivilegedlookupClass(Class lookupClass, int allowedModes) {
+ String name = lookupClass.getName();
+ if (name.startsWith("java.lang.invoke."))
+ throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
+
+ // For caller-sensitive MethodHandles.lookup()
+ // disallow lookup more restricted packages
+ if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
+ if (name.startsWith("java.") ||
+ (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
+ throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
+ }
+ }
+ }
+
+ /**
+ * Displays the name of the class from which lookups are to be made.
+ * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
+ * If there are restrictions on the access permitted to this lookup,
+ * this is indicated by adding a suffix to the class name, consisting
+ * of a slash and a keyword. The keyword represents the strongest
+ * allowed access, and is chosen as follows:
+ *
+ *
+ * If none of the above cases apply, it is the case that full
+ * access (public, package, private, and protected) is allowed.
+ * In this case, no suffix is added.
+ * This is true only of an object obtained originally from
+ * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
+ * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
+ * always have restricted access, and will display a suffix.
+ *
+ * @param refc the class from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is not {@code static},
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public
+ MethodHandle findStatic(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
+ return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
+ }
+
+ /**
+ * Produces a method handle for a virtual method.
+ * The type of the method handle will be that of the method,
+ * with the receiver type (usually {@code refc}) prepended.
+ * The method and all its argument types must be accessible to the lookup object.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
+ "asList", methodType(List.class, Object[].class));
+assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
+ * }
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is {@code static}
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findVirtual(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ if (refc == MethodHandle.class) {
+ MethodHandle mh = findVirtualForMH(name, type);
+ if (mh != null) return mh;
+ }
+ byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
+ MemberName method = resolveOrFail(refKind, refc, name, type);
+ return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
+ }
+ private MethodHandle findVirtualForMH(String name, MethodType type) {
+ // these names require special lookups because of the implicit MethodType argument
+ if ("invoke".equals(name))
+ return invoker(type);
+ if ("invokeExact".equals(name))
+ return exactInvoker(type);
+ assert(!MemberName.isMethodHandleInvokeName(name));
+ return null;
+ }
+
+ /**
+ * Produces a method handle which creates an object and initializes it, using
+ * the constructor of the specified type.
+ * The parameter types of the method handle will be those of the constructor,
+ * while the return type will be a reference to the constructor's class.
+ * The constructor and all its argument types must be accessible to the lookup object.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_concat = publicLookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
+ "hashCode", methodType(int.class));
+MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
+ "hashCode", methodType(int.class));
+assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
+assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
+assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
+// interface method:
+MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
+ "subSequence", methodType(CharSequence.class, int.class, int.class));
+assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
+// constructor "internal method" must be accessed differently:
+MethodType MT_newString = methodType(void.class); //()V for new String()
+try { assertEquals("impossible", lookup()
+ .findVirtual(String.class, "
+ * @param refc the class or interface from which the method is accessed
+ * @param type the type of the method, with the receiver argument omitted, and a void return type
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the constructor does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findConstructor(Class refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ String name = "{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_newArrayList = publicLookup().findConstructor(
+ ArrayList.class, methodType(void.class, Collection.class));
+Collection orig = Arrays.asList("x", "y");
+Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
+assert(orig != copy);
+assertEquals(orig, copy);
+// a variable-arity constructor:
+MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
+ ProcessBuilder.class, methodType(void.class, String[].class));
+ProcessBuilder pb = (ProcessBuilder)
+ MH_newProcessBuilder.invoke("x", "y", "z");
+assertEquals("[x, y, z]", pb.command().toString());
+ * }
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method (which must not be "<init>")
+ * @param type the type of the method, with the receiver argument omitted
+ * @param specialCaller the proposed calling class to perform the {@code invokespecial}
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSpecial(Class refc, String name, MethodType type,
+ Class specialCaller) throws NoSuchMethodException, IllegalAccessException {
+ checkSpecialCaller(specialCaller);
+ Lookup specialLookup = this.in(specialCaller);
+ MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
+ return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
+ }
+
+ /**
+ * Produces a method handle giving read access to a non-static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle's single argument will be the instance containing
+ * the field.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_getField, refc, name, type);
+ return getDirectField(REF_getField, refc, field);
+ }
+
+ /**
+ * Produces a method handle giving write access to a non-static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take two arguments, the instance containing
+ * the field, and the value to be stored.
+ * The second argument will be of the field's value type.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_putField, refc, name, type);
+ return getDirectField(REF_putField, refc, field);
+ }
+
+ /**
+ * Produces a method handle giving read access to a static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle will take no arguments.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+static class Listie extends ArrayList {
+ public String toString() { return "[wee Listie]"; }
+ static Lookup lookup() { return MethodHandles.lookup(); }
+}
+...
+// no access to constructor via invokeSpecial:
+MethodHandle MH_newListie = Listie.lookup()
+ .findConstructor(Listie.class, methodType(void.class));
+Listie l = (Listie) MH_newListie.invokeExact();
+try { assertEquals("impossible", Listie.lookup().findSpecial(
+ Listie.class, "
+ * where {@code defc} is either {@code receiver.getClass()} or a super
+ * type of that class, in which the requested method is accessible
+ * to the lookup class.
+ * (Note that {@code bindTo} does not preserve variable arity.)
+ * @param receiver the object from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ * @see MethodHandle#bindTo
+ * @see #findVirtual
+ */
+ public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ Class refc = receiver.getClass(); // may get NPE
+ MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
+ MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
+ return mh.bindReceiver(receiver).setVarargs(method);
+ }
+
+ /**
+ * Makes a direct method handle
+ * to m, if the lookup class has permission.
+ * If m is non-static, the receiver argument is treated as an initial argument.
+ * If m is virtual, overriding is respected on every call.
+ * Unlike the Core Reflection API, exceptions are not wrapped.
+ * The type of the method handle will be that of the method,
+ * with the receiver type prepended (but only if it is non-static).
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * If m is not public, do not share the resulting handle with untrusted parties.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle mh0 = lookup().findVirtual(defc, name, type);
+MethodHandle mh1 = mh0.bindTo(receiver);
+MethodType mt1 = mh1.type();
+if (mh0.isVarargsCollector())
+ mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
+return mh1;
+ * }
+ *
+ *
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
+ * @return a method handle suitable for invoking any method handle of the given type
+ * @throws NullPointerException if {@code type} is null
+ * @throws IllegalArgumentException if {@code leadingArgCount} is not in
+ * the range from 0 to {@code type.parameterCount()} inclusive,
+ * or if the resulting method handle's type would have
+ * too many parameters
+ */
+ static public
+ MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
+ if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
+ throw new IllegalArgumentException("bad argument count "+leadingArgCount);
+ return type.invokers().spreadInvoker(leadingArgCount);
+ }
+
+ /**
+ * Produces a special invoker method handle which can be used to
+ * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ * {@code
+MethodHandle invoker = MethodHandles.invoker(type);
+int spreadArgCount = type.parameterCount() - leadingArgCount;
+invoker = invoker.asSpreader(Object[].class, spreadArgCount);
+return invoker;
+ * }
+ *
+ * @param target the method handle to invoke after arguments are retyped
+ * @param newType the expected type of the new method handle
+ * @return a method handle which delegates to the target after performing
+ * any necessary argument conversions, and arranges for any
+ * necessary return value conversions
+ * @throws NullPointerException if either argument is null
+ * @throws WrongMethodTypeException if the conversion cannot be made
+ * @see MethodHandle#asType
+ */
+ public static
+ MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
+ if (!target.type().isCastableTo(newType)) {
+ throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
+ }
+ return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
+ }
+
+ /**
+ * Produces a method handle which adapts the calling sequence of the
+ * given method handle to a new type, by reordering the arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ *
+ * @param target the method handle to invoke after arguments are reordered
+ * @param newType the expected type of the new method handle
+ * @param reorder an index array which controls the reordering
+ * @return a method handle which delegates to the target after it
+ * drops unused arguments and moves and/or duplicates the other arguments
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if the index array length is not equal to
+ * the arity of the target, or if any index array element
+ * not a valid index for a parameter of {@code newType},
+ * or if two corresponding parameter types in
+ * {@code target.type()} and {@code newType} are not identical,
+ */
+ public static
+ MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
+ checkReorder(reorder, newType, target.type());
+ return target.permuteArguments(newType, reorder);
+ }
+
+ private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
+ if (newType.returnType() != oldType.returnType())
+ throw newIllegalArgumentException("return types do not match",
+ oldType, newType);
+ if (reorder.length == oldType.parameterCount()) {
+ int limit = newType.parameterCount();
+ boolean bad = false;
+ for (int j = 0; j < reorder.length; j++) {
+ int i = reorder[j];
+ if (i < 0 || i >= limit) {
+ bad = true; break;
+ }
+ Class src = newType.parameterType(i);
+ Class dst = oldType.parameterType(j);
+ if (src != dst)
+ throw newIllegalArgumentException("parameter types do not match after reorder",
+ oldType, newType);
+ }
+ if (!bad) return;
+ }
+ throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
+ }
+
+ /**
+ * Produces a method handle of the requested return type which returns the given
+ * constant value every time it is invoked.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodType intfn1 = methodType(int.class, int.class);
+MethodType intfn2 = methodType(int.class, int.class, int.class);
+MethodHandle sub = ... (int x, int y) -> (x-y) ...;
+assert(sub.type().equals(intfn2));
+MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
+MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
+assert((int)rsub.invokeExact(1, 100) == 99);
+MethodHandle add = ... (int x, int y) -> (x+y) ...;
+assert(add.type().equals(intfn2));
+MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
+assert(twice.type().equals(intfn1));
+assert((int)twice.invokeExact(21) == 42);
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
+MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
+assertEquals(bigType, d0.type());
+assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
+ * }
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the target is null,
+ * or if the {@code valueTypes} list or any of its elements is null
+ * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
+ * or if {@code pos} is negative or greater than the arity of the target,
+ * or if the new method handle's type would have too many parameters
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, List
+ * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
+ *
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle d0 = dropArguments(cat, 0, String.class);
+assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
+MethodHandle d1 = dropArguments(cat, 1, String.class);
+assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
+MethodHandle d2 = dropArguments(cat, 2, String.class);
+assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
+MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
+assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
+ * }
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the target is null,
+ * or if the {@code valueTypes} array or any of its elements is null
+ * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
+ * or if {@code pos} is negative or greater than the arity of the target,
+ * or if the new method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, Class... valueTypes) {
+ return dropArguments(target, pos, Arrays.asList(valueTypes));
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * one or more of its arguments, each with its own unary filter function,
+ * and then calling the target with each pre-processed argument
+ * replaced by the result of its corresponding filter function.
+ *
+ * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
+ *
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle upcase = lookup().findVirtual(String.class,
+ "toUpperCase", methodType(String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle f0 = filterArguments(cat, 0, upcase);
+assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
+MethodHandle f1 = filterArguments(cat, 1, upcase);
+assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
+MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
+assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
+ * }
+ *
+ * @param target the method handle to invoke after arguments are filtered
+ * @param pos the position of the first argument to filter
+ * @param filters method handles to call initially on filtered arguments
+ * @return method handle which incorporates the specified argument filtering logic
+ * @throws NullPointerException if the target is null
+ * or if the {@code filters} array is null
+ * @throws IllegalArgumentException if a non-null element of {@code filters}
+ * does not match a corresponding argument type of target as described above,
+ * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
+ * or if the resulting method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
+ MethodType targetType = target.type();
+ MethodHandle adapter = target;
+ MethodType adapterType = null;
+ assert((adapterType = targetType) != null);
+ int maxPos = targetType.parameterCount();
+ if (pos + filters.length > maxPos)
+ throw newIllegalArgumentException("too many filters");
+ int curPos = pos-1; // pre-incremented
+ for (MethodHandle filter : filters) {
+ curPos += 1;
+ if (filter == null) continue; // ignore null elements of filters
+ adapter = filterArgument(adapter, curPos, filter);
+ assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
+ }
+ assert(adapterType.equals(adapter.type()));
+ return adapter;
+ }
+
+ /*non-public*/ static
+ MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ if (filterType.parameterCount() != 1
+ || filterType.returnType() != targetType.parameterType(pos))
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * a sub-sequence of its arguments with a filter (another method handle).
+ * The pre-processed arguments are replaced by the result (if any) of the
+ * filter function.
+ * The target is then called on the modified (usually shortened) argument list.
+ * {@code
+ * V target(P... p, A[i]... a[i], B... b);
+ * A[i] filter[i](V[i]);
+ * T adapter(P... p, V[i]... v[i], B... b) {
+ * return target(p..., f[i](v[i])..., b...);
+ * }
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle deepToString = publicLookup()
+ .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
+
+MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
+assertEquals("[strange]", (String) ts1.invokeExact("strange"));
+
+MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
+assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
+
+MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
+MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
+assertEquals("[top, [up, down], strange]",
+ (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
+
+MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
+assertEquals("[top, [up, down], [strange]]",
+ (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
+
+MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
+assertEquals("[top, [[up, down, strange], charm], bottom]",
+ (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
+ * }
+ * {@code
+ * T target(A...,V,C...);
+ * V filter(B...);
+ * T adapter(A... a,B... b,C... c) {
+ * V v = filter(b...);
+ * return target(a...,v,c...);
+ * }
+ * // and if the filter has no arguments:
+ * T target2(A...,V,C...);
+ * V filter2();
+ * T adapter2(A... a,C... c) {
+ * V v = filter2();
+ * return target2(a...,v,c...);
+ * }
+ * // and if the filter has a void return:
+ * T target3(A...,C...);
+ * void filter3(B...);
+ * void adapter3(A... a,B... b,C... c) {
+ * filter3(b...);
+ * return target3(a...,c...);
+ * }
+ * }
+ * If the target method handle consumes no arguments besides than the result
+ * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
+ * is equivalent to {@code filterReturnValue(coll, mh)}.
+ * If the filter method handle {@code coll} consumes one argument and produces
+ * a non-void result, then {@code collectArguments(mh, N, coll)}
+ * is equivalent to {@code filterArguments(mh, N, coll)}.
+ * Other equivalences are possible but would require argument permutation.
+ *
+ * @param target the method handle to invoke after filtering the subsequence of arguments
+ * @param pos the position of the first adapter argument to pass to the filter,
+ * and/or the target argument which receives the result of the filter
+ * @param filter method handle to call on the subsequence of arguments
+ * @return method handle which incorporates the specified argument subsequence filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the return type of {@code filter}
+ * is non-void and is not the same as the {@code pos} argument of the target,
+ * or if {@code pos} is not between 0 and the target's arity, inclusive,
+ * or if the resulting method handle's type would have
+ * too many parameters
+ * @see MethodHandles#foldArguments
+ * @see MethodHandles#filterArguments
+ * @see MethodHandles#filterReturnValue
+ */
+ public static
+ MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ if (filterType.returnType() != void.class &&
+ filterType.returnType() != targetType.parameterType(pos))
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
+ }
+
+ /**
+ * Adapts a target method handle by post-processing
+ * its return value (if any) with a filter (another method handle).
+ * The result of the filter is returned from the adapter.
+ * {@code
+ * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
+ * mh = MethodHandles.foldArguments(mh, coll); //step 1
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle length = lookup().findVirtual(String.class,
+ "length", methodType(int.class));
+System.out.println((String) cat.invokeExact("x", "y")); // xy
+MethodHandle f0 = filterReturnValue(cat, length);
+System.out.println((int) f0.invokeExact("x", "y")); // 2
+ * }
+ * @param target the method handle to invoke before filtering the return value
+ * @param filter method handle to call on the return value
+ * @return method handle which incorporates the specified return value filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the argument list of {@code filter}
+ * does not match the return type of target as described above
+ */
+ public static
+ MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ Class rtype = targetType.returnType();
+ int filterValues = filterType.parameterCount();
+ if (filterValues == 0
+ ? (rtype != void.class)
+ : (rtype != filterType.parameterType(0)))
+ throw newIllegalArgumentException("target and filter types do not match", target, filter);
+ // result = fold( lambda(retval, arg...) { filter(retval) },
+ // lambda( arg...) { target(arg...) } )
+ return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * some of its arguments, and then calling the target with
+ * the result of the pre-processing, inserted into the original
+ * sequence of arguments.
+ * {@code
+ * V target(A...);
+ * T filter(V);
+ * T adapter(A... a) {
+ * V v = target(a...);
+ * return filter(v);
+ * }
+ * // and if the target has a void return:
+ * void target2(A...);
+ * T filter2();
+ * T adapter2(A... a) {
+ * target2(a...);
+ * return filter2();
+ * }
+ * // and if the filter has a void return:
+ * V target3(A...);
+ * void filter3(V);
+ * void adapter3(A... a) {
+ * V v = target3(a...);
+ * filter3(v);
+ * }
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
+ "println", methodType(void.class, String.class))
+ .bindTo(System.out);
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
+MethodHandle catTrace = foldArguments(cat, trace);
+// also prints "boo":
+assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
+ * }
+ * @param target the method handle to invoke after arguments are combined
+ * @param combiner method handle to call initially on the incoming arguments
+ * @return method handle which incorporates the specified argument folding logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if {@code combiner}'s return type
+ * is non-void and not the same as the first argument type of
+ * the target, or if the initial {@code N} argument types
+ * of the target
+ * (skipping one matching the {@code combiner}'s return type)
+ * are not identical with the argument types of {@code combiner}
+ */
+ public static
+ MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
+ int pos = 0;
+ MethodType targetType = target.type();
+ MethodType combinerType = combiner.type();
+ int foldPos = pos;
+ int foldArgs = combinerType.parameterCount();
+ int foldVals = combinerType.returnType() == void.class ? 0 : 1;
+ int afterInsertPos = foldPos + foldVals;
+ boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
+ if (ok && !(combinerType.parameterList()
+ .equals(targetType.parameterList().subList(afterInsertPos,
+ afterInsertPos + foldArgs))))
+ ok = false;
+ if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
+ ok = false;
+ if (!ok)
+ throw misMatchedTypes("target and combiner types", targetType, combinerType);
+ MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
+ return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
+ }
+
+ /**
+ * Makes a method handle which adapts a target method handle,
+ * by guarding it with a test, a boolean-valued method handle.
+ * If the guard fails, a fallback handle is called instead.
+ * All three method handles must have the same corresponding
+ * argument and return types, except that the return type
+ * of the test must be boolean, and the test is allowed
+ * to have fewer arguments than the other two method handles.
+ * {@code
+ * // there are N arguments in A...
+ * T target(V, A[N]..., B...);
+ * V combiner(A...);
+ * T adapter(A... a, B... b) {
+ * V v = combiner(a...);
+ * return target(v, a..., b...);
+ * }
+ * // and if the combiner has a void return:
+ * T target2(A[N]..., B...);
+ * void combiner2(A...);
+ * T adapter2(A... a, B... b) {
+ * combiner2(a...);
+ * return target2(a..., b...);
+ * }
+ * }
+ * Note that the test arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the test, and so are passed unchanged
+ * from the caller to the target or fallback as appropriate.
+ * @param test method handle used for test, must return boolean
+ * @param target method handle to call if test passes
+ * @param fallback method handle to call if test fails
+ * @return method handle which incorporates the specified if/then/else logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code test} does not return boolean,
+ * or if all three method types do not match (with the return
+ * type of {@code test} changed to match that of the target).
+ */
+ public static
+ MethodHandle guardWithTest(MethodHandle test,
+ MethodHandle target,
+ MethodHandle fallback) {
+ MethodType gtype = test.type();
+ MethodType ttype = target.type();
+ MethodType ftype = fallback.type();
+ if (!ttype.equals(ftype))
+ throw misMatchedTypes("target and fallback types", ttype, ftype);
+ if (gtype.returnType() != boolean.class)
+ throw newIllegalArgumentException("guard type is not a predicate "+gtype);
+ List{@code
+ * boolean test(A...);
+ * T target(A...,B...);
+ * T fallback(A...,B...);
+ * T adapter(A... a,B... b) {
+ * if (test(a...))
+ * return target(a..., b...);
+ * else
+ * return fallback(a..., b...);
+ * }
+ * }
+ * Note that the saved arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the target, and so are passed unchanged
+ * from the caller to the handler, if the handler is invoked.
+ * {@code
+ * T target(A..., B...);
+ * T handler(ExType, A...);
+ * T adapter(A... a, B... b) {
+ * try {
+ * return target(a..., b...);
+ * } catch (ExType ex) {
+ * return handler(ex, a...);
+ * }
+ * }
+ * }