/*

 * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package java.lang.invoke;

import java.lang.reflect.*;

/**

 * This class consists exclusively of static methods that operate on or return

 * method handles. They fall into several categories:

 * <ul>

 * <li>Lookup methods which help create method handles for methods and fields.

 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.

 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.

 * </ul>

 * <p>

 * @author John Rose, JSR 292 EG

 * @since 1.7

 */

public class MethodHandles {

    private MethodHandles() { }  // do not instantiate

    //// 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 <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.

     * Factory methods on the lookup object can create

     * <a href="MethodHandleInfo.html#directmh">direct method handles</a>

     * for any member that the caller has access to via bytecodes,

     * including protected and private fields and methods.

     * This lookup object is a <em>capability</em> which may be delegated to trusted agents.

     * Do not store it in place where untrusted code can access it.

     * <p>

     * This method is caller sensitive, which means that it may return different

     * values to different callers.

     * <p>

     * 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

     * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>

     * 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() {

        throw new IllegalStateException("Implement me!");

//        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.

     * <p>

     * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}

     * of this lookup object will be {@link java.lang.Object}.

     *

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * 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

     * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.

     * Also, it cannot access

     * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.

     * @return a lookup object which is trusted minimally

     */

    public static Lookup publicLookup() {

        return Lookup.PUBLIC_LOOKUP;

    }

    /**

     * Performs an unchecked "crack" of a

     * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.

     * 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.

     * <p>

     * If there is a security manager, its {@code checkPermission} method

     * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.

     * @param <T> the desired type of the result, either {@link Member} or a subtype

     * @param target a direct method handle to crack into symbolic reference components

     * @param expected a class object representing the desired result type {@code T}

     * @return a reference to the method, constructor, or field object

     * @exception SecurityException if the caller is not privileged to call {@code setAccessible}

     * @exception NullPointerException if either argument is {@code null}

     * @exception IllegalArgumentException if the target is not a direct method handle

     * @exception ClassCastException if the member is not of the expected type

     * @since 1.8

     */

    public static <T extends Member> T

    reflectAs(Class<T> expected, MethodHandle target) {

        throw new IllegalStateException();

    }

    // Copied from AccessibleObject, as used by Method.setAccessible, etc.:

//    static final private java.security.Permission ACCESS_PERMISSION =

//        new ReflectPermission("suppressAccessChecks");

    static Lookup findFor(Class<?> clazz) {

        Object o = clazz;

        if (o instanceof Class) {

            return new Lookup(clazz, Lookup.ALL_MODES);

        }

        throw new IllegalArgumentException("Expecting class: " + o);

    }

    /**

     * A <em>lookup object</em> is a factory for creating method handles,

     * when the creation requires access checking.

     * Method handles do not perform

     * access checks when they are called, but rather when they are created.

     * Therefore, method handle access

     * restrictions must be enforced when a method handle is created.

     * The caller class against which those restrictions are enforced

     * is known as the {@linkplain #lookupClass lookup class}.

     * <p>

     * 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.

     *

     * <h1><a name="lookups"></a>Lookup Factory Methods</h1>

     * 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 <em>bytecode behavior</em>.

     * (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:

     * <table border=1 cellpadding=5 summary="lookup method behaviors">

     * <tr>

     *     <th><a name="equiv"></a>lookup expression</th>

     *     <th>member</th>

     *     <th>bytecode behavior</th>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>

     *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>

     *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>

     *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>

     *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>

     *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>

     *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>

     *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>

     *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>

     *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>

     *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>

     *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>

     *     <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>

     *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>

     * </tr>

     * </table>

     *

     * Here, the type {@code C} is the class or interface being searched for a member,

     * documented as a parameter named {@code refc} in the lookup methods.

     * The method type {@code MT} is composed from the return type {@code T}

     * and the sequence of argument types {@code A*}.

     * The constructor also has a sequence of argument types {@code A*} and

     * is deemed to return the newly-created object of type {@code C}.

     * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.

     * The formal parameter {@code this} stands for the self-reference of type {@code C};

     * if it is present, it is always the leading argument to the method handle invocation.

     * (In the case of some {@code protected} members, {@code this} may be

     * restricted in type to the lookup class; see below.)

     * The name {@code arg} stands for all the other method handle arguments.

     * In the code examples for the Core Reflection API, the name {@code thisOrNull}

     * stands for a null reference if the accessed method or field is static,

     * and {@code this} otherwise.

     * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand

     * for reflective objects corresponding to the given members.

     * <p>

     * 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.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * The equivalence between looked-up method handles and underlying

     * class members and bytecode behaviors

     * can break down in a few ways:

     * <ul style="font-size:smaller;">

     * <li>If {@code C} is not symbolically accessible from the lookup class's loader,

     * the lookup can still succeed, even when there is no equivalent

     * Java expression or bytecoded constant.

     * <li>Likewise, if {@code T} or {@code MT}

     * is not symbolically accessible from the lookup class's loader,

     * the lookup can still succeed.

     * For example, lookups for {@code MethodHandle.invokeExact} and

     * {@code MethodHandle.invoke} will always succeed, regardless of requested type.

     * <li>If there is a security manager installed, it can forbid the lookup

     * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).

     * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}

     * constant is not subject to security manager checks.

     * <li>If the looked-up method has a

     * <a href="MethodHandle.html#maxarity">very large arity</a>,

     * the method handle creation may fail, due to the method handle

     * type having too many parameters.

     * </ul>

     *

     * <h1><a name="access"></a>Access checking</h1>

     * 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.

     * <p>

     * 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.

     * <p>

     * 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.

     * <p>

     * 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:

     * <ul>

     * <li>NoSuchMethodException &mdash; if a method is requested but does not exist

     * <li>NoSuchFieldException &mdash; if a field is requested but does not exist

     * <li>IllegalAccessException &mdash; if the member exists but an access check fails

     * </ul>

     * <p>

     * 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 <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>

     * to executing the compiled, verified, and resolved call to {@code M}.

     * The same point is true of fields and constructors.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * 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.

     * <p>

     * 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.

     * <p>

     * The JVM imposes a similar requirement on {@code invokespecial} instruction,

     * that the receiver argument must match both the resolved method <em>and</em>

     * 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.)

     * <p>

     * The JVM represents constructors and static initializer blocks as internal methods

     * with special names ({@code "<init>"} and {@code "<clinit>"}).

     * The internal syntax of invocation instructions allows them to refer to such internal

     * methods as if they were normal methods, but the JVM bytecode verifier rejects them.

     * A lookup of such an internal method will produce a {@code NoSuchMethodException}.

     * <p>

     * 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.

     * <p>

     * 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.

     *

     * <p style="font-size:smaller;">

     * <a name="privacc"></a>

     * <em>Discussion of private access:</em>

     * We say that a lookup has <em>private access</em>

     * 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:

     * <ul style="font-size:smaller;">

     * <li>access private fields, methods, and constructors of the lookup class

     * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,

     *     such as {@code Class.forName}

     * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions

     * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>

     *     for classes accessible to the lookup class

     * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes

     *     within the same package member

     * </ul>

     * <p style="font-size:smaller;">

     * 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 <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions

     * can be reliably determined and emulated by method handles.

     *

     * <h1><a name="secmgr"></a>Security manager interactions</h1>

     * 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}).

     * <p>

     * 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 <em>not present</em>

     * if the current lookup object does not have

     * <a href="MethodHandles.Lookup.html#privacc">private access</a>.

     * The calls are made according to the following rules:

     * <ul>

     * <li><b>Step 1:</b>

     *     If {@code lookc} is not present, or if its class loader is not

     *     the same as or an ancestor of the class loader of {@code refc},

     *     then {@link SecurityManager#checkPackageAccess

     *     smgr.checkPackageAccess(refcPkg)} is called,

     *     where {@code refcPkg} is the package of {@code refc}.

     * <li><b>Step 2:</b>

     *     If the retrieved member is not public and

     *     {@code lookc} is not present, then

     *     {@link SecurityManager#checkPermission smgr.checkPermission}

     *     with {@code RuntimePermission("accessDeclaredMembers")} is called.

     * <li><b>Step 3:</b>

     *     If the retrieved member is not public,

     *     and if {@code lookc} is not present,

     *     and if {@code defc} and {@code refc} are different,

     *     then {@link SecurityManager#checkPackageAccess

     *     smgr.checkPackageAccess(defcPkg)} is called,

     *     where {@code defcPkg} is the package of {@code defc}.

     * </ul>

     * 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.

     *

     * <h1><a name="callsens"></a>Caller sensitive methods</h1>

     * A small number of Java methods have a special property called caller sensitivity.

     * A <em>caller-sensitive</em> method can behave differently depending on the

     * identity of its immediate caller.

     * <p>

     * If a method handle for a caller-sensitive method is requested,

     * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> 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.

     * <p>

     * In cases where the lookup object is

     * {@link MethodHandles#publicLookup() publicLookup()},

     * or some other lookup object without

     * <a href="MethodHandles.Lookup.html#privacc">private access</a>,

     * 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}.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * 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.

     * <p style="font-size:smaller;">

     * 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.

     * <p style="font-size:smaller;">

     * 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.

         *  <p>

         *  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)}.

         *  <p>

         *  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:

        }

        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}.

         * <p>

         * 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:<ul>

         * <li>If the new lookup class differs from the old one,

         * protected members will not be accessible by virtue of inheritance.

         * (Protected members may continue to be accessible because of package sharing.)

         * <li>If the new lookup class is in a different package

         * than the old one, protected and default (package) members will not be accessible.

         * <li>If the new lookup class is not within the same package member

         * as the old one, private members will not be accessible.

         * <li>If the new lookup class is not accessible to the old lookup class,

         * then no members, not even public members, will be accessible.

         * (In all other cases, public members will continue to be accessible.)

         * </ul>

         *

         * @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) {

            throw new IllegalStateException();

        }

        /** 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);

        /**

         * 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:

         * <ul>

         * <li>If no access is allowed, the suffix is "/noaccess".

         * <li>If only public access is allowed, the suffix is "/public".

         * <li>If only public and package access are allowed, the suffix is "/package".

         * <li>If only public, package, and private access are allowed, the suffix is "/private".

         * </ul>

         * 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.

         * <p>

         * (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.

         * <p>

         * 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.

         * <p>

         * If the returned method handle is invoked, the method's class will

         * be initialized, if it has not already been initialized.

         * <p><b>Example:</b>

         * <blockquote><pre>{@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());

         * }</pre></blockquote>

         * @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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public

        MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * 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.

         * <p>

         * 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.)

         * <p>

         * 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.

         * <p>

         * 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.

         * <p>

         * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> 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.

         *

         * <b>Example:</b>

         * <blockquote><pre>{@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, "<init>", MT_newString));

 } catch (NoSuchMethodException ex) { } // OK

MethodHandle MH_newString = publicLookup()

  .findConstructor(String.class, MT_newString);

assertEquals("", (String) MH_newString.invokeExact());

         * }</pre></blockquote>

         *

         * @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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * 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.

         * <p>

         * The requested type must have a return type of {@code void}.

         * (This is consistent with the JVM's treatment of constructor type descriptors.)

         * <p>

         * 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.

         * <p>

         * If the returned method handle is invoked, the constructor's class will

         * be initialized, if it has not already been initialized.

         * <p><b>Example:</b>

         * <blockquote><pre>{@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());

         * }</pre></blockquote>

         * @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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * Produces an early-bound method handle for a virtual method.

         * It will bypass checks for overriding methods on the receiver,

         * <a href="MethodHandles.Lookup.html#equiv">as if called</a> 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.)

         * The method and all its argument types must be accessible

         * to the lookup object.

         * <p>

         * Before method resolution,

         * if the explicitly specified caller class is not identical with the

         * lookup class, or if this lookup object does not have

         * <a href="MethodHandles.Lookup.html#privacc">private access</a>

         * privileges, the access fails.

         * <p>

         * 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.

         * <p style="font-size:smaller;">

         * <em>(Note:  JVM internal methods named {@code "<init>"} are not visible to this API,

         * even though the {@code invokespecial} instruction can refer to them

         * in special circumstances.  Use {@link #findConstructor findConstructor}

         * to access instance initialization methods in a safe manner.)</em>

         * <p><b>Example:</b>

         * <blockquote><pre>{@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, "<init>", methodType(void.class), Listie.class));

 } catch (NoSuchMethodException ex) { } // OK

// access to super and self methods via invokeSpecial:

MethodHandle MH_super = Listie.lookup().findSpecial(

  ArrayList.class, "toString" , methodType(String.class), Listie.class);

MethodHandle MH_this = Listie.lookup().findSpecial(

  Listie.class, "toString" , methodType(String.class), Listie.class);

MethodHandle MH_duper = Listie.lookup().findSpecial(

  Object.class, "toString" , methodType(String.class), Listie.class);

assertEquals("[]", (String) MH_super.invokeExact(l));

assertEquals(""+l, (String) MH_this.invokeExact(l));

assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method

try { assertEquals("inaccessible", Listie.lookup().findSpecial(

        String.class, "toString", methodType(String.class), Listie.class));

 } catch (IllegalAccessException ex) { } // OK

Listie subl = new Listie() { public String toString() { return "[subclass]"; } };

assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method

         * }</pre></blockquote>

         *

         * @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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,

                                        Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * 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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * 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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * 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.

         * <p>

         * 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

         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>

         * @throws NullPointerException if any argument is null

         */

        public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws IllegalAccessException {

            throw new IllegalStateException();

        }

        /**

         * 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.