/*

  * Copyright (c) 1996, 2011, 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

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  */

 package java.io;

 import java.lang.ref.Reference;

 import java.lang.ref.ReferenceQueue;

 import java.lang.ref.SoftReference;

 import java.lang.ref.WeakReference;

 import java.lang.reflect.Constructor;

 import java.lang.reflect.Field;

 import java.lang.reflect.InvocationTargetException;

 import java.lang.reflect.Member;

 import java.lang.reflect.Method;

 import java.lang.reflect.Modifier;

 import java.lang.reflect.Proxy;

 import java.security.AccessController;

 import java.security.MessageDigest;

 import java.security.NoSuchAlgorithmException;

 import java.security.PrivilegedAction;

 import java.util.ArrayList;

 import java.util.Arrays;

 import java.util.Collections;

 import java.util.Comparator;

 import java.util.HashSet;

 import java.util.Set;

 import java.util.concurrent.ConcurrentHashMap;

 import java.util.concurrent.ConcurrentMap;

 import sun.misc.Unsafe;

 import sun.reflect.ReflectionFactory;

 /**

  * Serialization's descriptor for classes.  It contains the name and

  * serialVersionUID of the class.  The ObjectStreamClass for a specific class

  * loaded in this Java VM can be found/created using the lookup method.

  *

  * <p>The algorithm to compute the SerialVersionUID is described in

  * <a href="../../../platform/serialization/spec/class.html#4100">Object

  * Serialization Specification, Section 4.6, Stream Unique Identifiers</a>.

  *

  * @author      Mike Warres

  * @author      Roger Riggs

  * @see ObjectStreamField

  * @see <a href="../../../platform/serialization/spec/class.html">Object Serialization Specification, Section 4, Class Descriptors</a>

  * @since   JDK1.1

  */

 public class ObjectStreamClass implements Serializable {

     /** serialPersistentFields value indicating no serializable fields */

     public static final ObjectStreamField[] NO_FIELDS =

         new ObjectStreamField[0];

     private static final long serialVersionUID = -6120832682080437368L;

     private static final ObjectStreamField[] serialPersistentFields =

         NO_FIELDS;

     /** reflection factory for obtaining serialization constructors */

     private static final ReflectionFactory reflFactory =

         AccessController.doPrivileged(

             new ReflectionFactory.GetReflectionFactoryAction());

     private static class Caches {

         /** cache mapping local classes -> descriptors */

         static final ConcurrentMap<WeakClassKey,Reference<?>> localDescs =

             new ConcurrentHashMap<>();

         /** cache mapping field group/local desc pairs -> field reflectors */

         static final ConcurrentMap<FieldReflectorKey,Reference<?>> reflectors =

             new ConcurrentHashMap<>();

         /** queue for WeakReferences to local classes */

         private static final ReferenceQueue<Class<?>> localDescsQueue =

             new ReferenceQueue<>();

         /** queue for WeakReferences to field reflectors keys */

         private static final ReferenceQueue<Class<?>> reflectorsQueue =

             new ReferenceQueue<>();

     }

     /** class associated with this descriptor (if any) */

     private Class<?> cl;

     /** name of class represented by this descriptor */

     private String name;

     /** serialVersionUID of represented class (null if not computed yet) */

     private volatile Long suid;

     /** true if represents dynamic proxy class */

     private boolean isProxy;

     /** true if represents enum type */

     private boolean isEnum;

     /** true if represented class implements Serializable */

     private boolean serializable;

     /** true if represented class implements Externalizable */

     private boolean externalizable;

     /** true if desc has data written by class-defined writeObject method */

     private boolean hasWriteObjectData;

     /**

      * true if desc has externalizable data written in block data format; this

      * must be true by default to accommodate ObjectInputStream subclasses which

      * override readClassDescriptor() to return class descriptors obtained from

      * ObjectStreamClass.lookup() (see 4461737)

      */

     private boolean hasBlockExternalData = true;

     /** exception (if any) thrown while attempting to resolve class */

     private ClassNotFoundException resolveEx;

     /** exception (if any) to throw if non-enum deserialization attempted */

     private InvalidClassException deserializeEx;

     /** exception (if any) to throw if non-enum serialization attempted */

     private InvalidClassException serializeEx;

     /** exception (if any) to throw if default serialization attempted */

     private InvalidClassException defaultSerializeEx;

     /** serializable fields */

     private ObjectStreamField[] fields;

     /** aggregate marshalled size of primitive fields */

     private int primDataSize;

     /** number of non-primitive fields */

     private int numObjFields;

     /** reflector for setting/getting serializable field values */

     private FieldReflector fieldRefl;

     /** data layout of serialized objects described by this class desc */

     private volatile ClassDataSlot[] dataLayout;

     /** serialization-appropriate constructor, or null if none */

     private Constructor cons;

     /** class-defined writeObject method, or null if none */

     private Method writeObjectMethod;

     /** class-defined readObject method, or null if none */

     private Method readObjectMethod;

     /** class-defined readObjectNoData method, or null if none */

     private Method readObjectNoDataMethod;

     /** class-defined writeReplace method, or null if none */

     private Method writeReplaceMethod;

     /** class-defined readResolve method, or null if none */

     private Method readResolveMethod;

     /** local class descriptor for represented class (may point to self) */

     private ObjectStreamClass localDesc;

     /** superclass descriptor appearing in stream */

     private ObjectStreamClass superDesc;

     /**

      * Initializes native code.

      */

     private static native void initNative();

     static {

         initNative();

     }

     /**

      * Find the descriptor for a class that can be serialized.  Creates an

      * ObjectStreamClass instance if one does not exist yet for class. Null is

      * returned if the specified class does not implement java.io.Serializable

      * or java.io.Externalizable.

      *

      * @param   cl class for which to get the descriptor

      * @return  the class descriptor for the specified class

      */

     public static ObjectStreamClass lookup(Class<?> cl) {

         return lookup(cl, false);

     }

     /**

      * Returns the descriptor for any class, regardless of whether it

      * implements {@link Serializable}.

      *

      * @param        cl class for which to get the descriptor

      * @return       the class descriptor for the specified class

      * @since 1.6

      */

     public static ObjectStreamClass lookupAny(Class<?> cl) {

         return lookup(cl, true);

     }

     /**

      * Returns the name of the class described by this descriptor.

      * This method returns the name of the class in the format that

      * is used by the {@link Class#getName} method.

      *

      * @return a string representing the name of the class

      */

     public String getName() {

         return name;

     }

     /**

      * Return the serialVersionUID for this class.  The serialVersionUID

      * defines a set of classes all with the same name that have evolved from a

      * common root class and agree to be serialized and deserialized using a

      * common format.  NonSerializable classes have a serialVersionUID of 0L.

      *

      * @return  the SUID of the class described by this descriptor

      */

     public long getSerialVersionUID() {

         // REMIND: synchronize instead of relying on volatile?

         if (suid == null) {

             suid = AccessController.doPrivileged(

                 new PrivilegedAction<Long>() {

                     public Long run() {

                         return computeDefaultSUID(cl);

                     }

                 }

             );

         }

         return suid.longValue();

     }

     /**

      * Return the class in the local VM that this version is mapped to.  Null

      * is returned if there is no corresponding local class.

      *

      * @return  the <code>Class</code> instance that this descriptor represents

      */

     public Class<?> forClass() {

         return cl;

     }

     /**

      * Return an array of the fields of this serializable class.

      *

      * @return  an array containing an element for each persistent field of

      *          this class. Returns an array of length zero if there are no

      *          fields.

      * @since 1.2

      */

     public ObjectStreamField[] getFields() {

         return getFields(true);

     }

     /**

      * Get the field of this class by name.

      *

      * @param   name the name of the data field to look for

      * @return  The ObjectStreamField object of the named field or null if

      *          there is no such named field.

      */

     public ObjectStreamField getField(String name) {

         return getField(name, null);

     }

     /**

      * Return a string describing this ObjectStreamClass.

      */

     public String toString() {

         return name + ": static final long serialVersionUID = " +

             getSerialVersionUID() + "L;";

     }

     /**

      * Looks up and returns class descriptor for given class, or null if class

      * is non-serializable and "all" is set to false.

      *

      * @param   cl class to look up

      * @param   all if true, return descriptors for all classes; if false, only

      *          return descriptors for serializable classes

      */

     static ObjectStreamClass lookup(Class<?> cl, boolean all) {

         if (!(all || Serializable.class.isAssignableFrom(cl))) {

             return null;

         }

         processQueue(Caches.localDescsQueue, Caches.localDescs);

         WeakClassKey key = new WeakClassKey(cl, Caches.localDescsQueue);

         Reference<?> ref = Caches.localDescs.get(key);

         Object entry = null;

         if (ref != null) {

             entry = ref.get();

         }

         EntryFuture future = null;

         if (entry == null) {

             EntryFuture newEntry = new EntryFuture();

             Reference<?> newRef = new SoftReference<>(newEntry);

             do {

                 if (ref != null) {

                     Caches.localDescs.remove(key, ref);

                 }

                 ref = Caches.localDescs.putIfAbsent(key, newRef);

                 if (ref != null) {

                     entry = ref.get();

                 }

             } while (ref != null && entry == null);

             if (entry == null) {

                 future = newEntry;

             }

         }

         if (entry instanceof ObjectStreamClass) {  // check common case first

             return (ObjectStreamClass) entry;

         }

         if (entry instanceof EntryFuture) {

             future = (EntryFuture) entry;

             if (future.getOwner() == Thread.currentThread()) {

                 /*

                  * Handle nested call situation described by 4803747: waiting

                  * for future value to be set by a lookup() call further up the

                  * stack will result in deadlock, so calculate and set the

                  * future value here instead.

                  */

                 entry = null;

             } else {

                 entry = future.get();

             }

         }

         if (entry == null) {

             try {

                 entry = new ObjectStreamClass(cl);

             } catch (Throwable th) {

                 entry = th;

             }

             if (future.set(entry)) {

                 Caches.localDescs.put(key, new SoftReference<Object>(entry));

             } else {

                 // nested lookup call already set future

                 entry = future.get();

             }

         }

         if (entry instanceof ObjectStreamClass) {

             return (ObjectStreamClass) entry;

         } else if (entry instanceof RuntimeException) {

             throw (RuntimeException) entry;

         } else if (entry instanceof Error) {

             throw (Error) entry;

         } else {

             throw new InternalError("unexpected entry: " + entry);

         }

     }

     /**

      * Placeholder used in class descriptor and field reflector lookup tables

      * for an entry in the process of being initialized.  (Internal) callers

      * which receive an EntryFuture belonging to another thread as the result

      * of a lookup should call the get() method of the EntryFuture; this will

      * return the actual entry once it is ready for use and has been set().  To

      * conserve objects, EntryFutures synchronize on themselves.

      */

     private static class EntryFuture {

         private static final Object unset = new Object();

         private final Thread owner = Thread.currentThread();

         private Object entry = unset;

         /**

          * Attempts to set the value contained by this EntryFuture.  If the

          * EntryFuture's value has not been set already, then the value is

          * saved, any callers blocked in the get() method are notified, and

          * true is returned.  If the value has already been set, then no saving

          * or notification occurs, and false is returned.

          */

         synchronized boolean set(Object entry) {

             if (this.entry != unset) {

                 return false;

             }

             this.entry = entry;

             notifyAll();

             return true;

         }

         /**

          * Returns the value contained by this EntryFuture, blocking if

          * necessary until a value is set.

          */

         synchronized Object get() {

             boolean interrupted = false;

             while (entry == unset) {

                 try {

                     wait();

                 } catch (InterruptedException ex) {

                     interrupted = true;

                 }

             }

             if (interrupted) {

                 AccessController.doPrivileged(

                     new PrivilegedAction<Void>() {

                         public Void run() {

                             Thread.currentThread().interrupt();

                             return null;

                         }

                     }

                 );

             }

             return entry;

         }

         /**

          * Returns the thread that created this EntryFuture.

          */

         Thread getOwner() {

             return owner;

         }

     }

     /**

      * Creates local class descriptor representing given class.

      */

     private ObjectStreamClass(final Class<?> cl) {

         this.cl = cl;

         name = cl.getName();

         isProxy = Proxy.isProxyClass(cl);

         isEnum = Enum.class.isAssignableFrom(cl);

         serializable = Serializable.class.isAssignableFrom(cl);

         externalizable = Externalizable.class.isAssignableFrom(cl);

         Class<?> superCl = cl.getSuperclass();

         superDesc = (superCl != null) ? lookup(superCl, false) : null;

         localDesc = this;

         if (serializable) {

             AccessController.doPrivileged(new PrivilegedAction<Void>() {

                 public Void run() {

                     if (isEnum) {

                         suid = Long.valueOf(0);

                         fields = NO_FIELDS;

                         return null;

                     }

                     if (cl.isArray()) {

                         fields = NO_FIELDS;

                         return null;

                     }

                     suid = getDeclaredSUID(cl);

                     try {

                         fields = getSerialFields(cl);

                         computeFieldOffsets();

                     } catch (InvalidClassException e) {

                         serializeEx = deserializeEx = e;

                         fields = NO_FIELDS;

                     }

                     if (externalizable) {

                         cons = getExternalizableConstructor(cl);

                     } else {

                         cons = getSerializableConstructor(cl);

                         writeObjectMethod = getPrivateMethod(cl, "writeObject",

                             new Class<?>[] { ObjectOutputStream.class },

                             Void.TYPE);

                         readObjectMethod = getPrivateMethod(cl, "readObject",

                             new Class<?>[] { ObjectInputStream.class },

                             Void.TYPE);

                         readObjectNoDataMethod = getPrivateMethod(

                             cl, "readObjectNoData", null, Void.TYPE);

                         hasWriteObjectData = (writeObjectMethod != null);

                     }

                     writeReplaceMethod = getInheritableMethod(

                         cl, "writeReplace", null, Object.class);

                     readResolveMethod = getInheritableMethod(

                         cl, "readResolve", null, Object.class);

                     return null;

                 }

             });

         } else {

             suid = Long.valueOf(0);

             fields = NO_FIELDS;

         }

         try {

             fieldRefl = getReflector(fields, this);

         } catch (InvalidClassException ex) {

             // field mismatches impossible when matching local fields vs. self

             throw new InternalError();

         }

         if (deserializeEx == null) {

             if (isEnum) {

                 deserializeEx = new InvalidClassException(name, "enum type");

             } else if (cons == null) {

                 deserializeEx = new InvalidClassException(

                     name, "no valid constructor");

             }

         }

         for (int i = 0; i < fields.length; i++) {

             if (fields[i].getField() == null) {

                 defaultSerializeEx = new InvalidClassException(

                     name, "unmatched serializable field(s) declared");

             }

         }

     }

     /**

      * Creates blank class descriptor which should be initialized via a

      * subsequent call to initProxy(), initNonProxy() or readNonProxy().

      */

     ObjectStreamClass() {

     }

     /**

      * Initializes class descriptor representing a proxy class.

      */

     void initProxy(Class<?> cl,

                    ClassNotFoundException resolveEx,

                    ObjectStreamClass superDesc)

         throws InvalidClassException

     {

         this.cl = cl;

         this.resolveEx = resolveEx;

         this.superDesc = superDesc;

         isProxy = true;

         serializable = true;

         suid = Long.valueOf(0);

         fields = NO_FIELDS;

         if (cl != null) {

             localDesc = lookup(cl, true);

             if (!localDesc.isProxy) {

                 throw new InvalidClassException(

                     "cannot bind proxy descriptor to a non-proxy class");

             }

             name = localDesc.name;

             externalizable = localDesc.externalizable;

             cons = localDesc.cons;

             writeReplaceMethod = localDesc.writeReplaceMethod;

             readResolveMethod = localDesc.readResolveMethod;

             deserializeEx = localDesc.deserializeEx;

         }

         fieldRefl = getReflector(fields, localDesc);

     }

     /**

      * Initializes class descriptor representing a non-proxy class.

      */

     void initNonProxy(ObjectStreamClass model,

                       Class<?> cl,

                       ClassNotFoundException resolveEx,

                       ObjectStreamClass superDesc)

         throws InvalidClassException

     {

         this.cl = cl;

         this.resolveEx = resolveEx;

         this.superDesc = superDesc;

         name = model.name;

         suid = Long.valueOf(model.getSerialVersionUID());

         isProxy = false;

         isEnum = model.isEnum;

         serializable = model.serializable;

         externalizable = model.externalizable;

         hasBlockExternalData = model.hasBlockExternalData;

         hasWriteObjectData = model.hasWriteObjectData;

         fields = model.fields;

         primDataSize = model.primDataSize;

         numObjFields = model.numObjFields;

         if (cl != null) {

             localDesc = lookup(cl, true);

             if (localDesc.isProxy) {

                 throw new InvalidClassException(

                     "cannot bind non-proxy descriptor to a proxy class");

             }

             if (isEnum != localDesc.isEnum) {

                 throw new InvalidClassException(isEnum ?

                     "cannot bind enum descriptor to a non-enum class" :

                     "cannot bind non-enum descriptor to an enum class");

             }

             if (serializable == localDesc.serializable &&

                 !cl.isArray() &&

                 suid.longValue() != localDesc.getSerialVersionUID())

             {

                 throw new InvalidClassException(localDesc.name,

                     "local class incompatible: " +

                     "stream classdesc serialVersionUID = " + suid +

                     ", local class serialVersionUID = " +

                     localDesc.getSerialVersionUID());

             }

             if (!classNamesEqual(name, localDesc.name)) {

                 throw new InvalidClassException(localDesc.name,

                     "local class name incompatible with stream class " +

                     "name \"" + name + "\"");

             }

             if (!isEnum) {

                 if ((serializable == localDesc.serializable) &&

                     (externalizable != localDesc.externalizable))

                 {

                     throw new InvalidClassException(localDesc.name,

                         "Serializable incompatible with Externalizable");

                 }

                 if ((serializable != localDesc.serializable) ||

                     (externalizable != localDesc.externalizable) ||

                     !(serializable || externalizable))

                 {

                     deserializeEx = new InvalidClassException(localDesc.name,

                         "class invalid for deserialization");

                 }

             }

             cons = localDesc.cons;

             writeObjectMethod = localDesc.writeObjectMethod;

             readObjectMethod = localDesc.readObjectMethod;

             readObjectNoDataMethod = localDesc.readObjectNoDataMethod;

             writeReplaceMethod = localDesc.writeReplaceMethod;

             readResolveMethod = localDesc.readResolveMethod;

             if (deserializeEx == null) {

                 deserializeEx = localDesc.deserializeEx;

             }

         }

         fieldRefl = getReflector(fields, localDesc);

         // reassign to matched fields so as to reflect local unshared settings

         fields = fieldRefl.getFields();

     }

     /**

      * Reads non-proxy class descriptor information from given input stream.

      * The resulting class descriptor is not fully functional; it can only be

      * used as input to the ObjectInputStream.resolveClass() and

      * ObjectStreamClass.initNonProxy() methods.

      */

     void readNonProxy(ObjectInputStream in)

         throws IOException, ClassNotFoundException

     {

         name = in.readUTF();

         suid = Long.valueOf(in.readLong());

         isProxy = false;

         byte flags = in.readByte();

         hasWriteObjectData =

             ((flags & ObjectStreamConstants.SC_WRITE_METHOD) != 0);

         hasBlockExternalData =

             ((flags & ObjectStreamConstants.SC_BLOCK_DATA) != 0);

         externalizable =

             ((flags & ObjectStreamConstants.SC_EXTERNALIZABLE) != 0);

         boolean sflag =

             ((flags & ObjectStreamConstants.SC_SERIALIZABLE) != 0);

         if (externalizable && sflag) {

             throw new InvalidClassException(

                 name, "serializable and externalizable flags conflict");

         }

         serializable = externalizable || sflag;

         isEnum = ((flags & ObjectStreamConstants.SC_ENUM) != 0);

         if (isEnum && suid.longValue() != 0L) {

             throw new InvalidClassException(name,

                 "enum descriptor has non-zero serialVersionUID: " + suid);

         }

         int numFields = in.readShort();

         if (isEnum && numFields != 0) {

             throw new InvalidClassException(name,

                 "enum descriptor has non-zero field count: " + numFields);

         }

         fields = (numFields > 0) ?

             new ObjectStreamField[numFields] : NO_FIELDS;

         for (int i = 0; i < numFields; i++) {

             char tcode = (char) in.readByte();

             String fname = in.readUTF();

             String signature = ((tcode == 'L') || (tcode == '[')) ?

                 in.readTypeString() : new String(new char[] { tcode });

             try {

                 fields[i] = new ObjectStreamField(fname, signature, false);

             } catch (RuntimeException e) {

                 throw (IOException) new InvalidClassException(name,

                     "invalid descriptor for field " + fname).initCause(e);

             }

         }

         computeFieldOffsets();

     }

     /**

      * Writes non-proxy class descriptor information to given output stream.

      */

     void writeNonProxy(ObjectOutputStream out) throws IOException {

         out.writeUTF(name);

         out.writeLong(getSerialVersionUID());

         byte flags = 0;

         if (externalizable) {

             flags |= ObjectStreamConstants.SC_EXTERNALIZABLE;

             int protocol = out.getProtocolVersion();

             if (protocol != ObjectStreamConstants.PROTOCOL_VERSION_1) {

                 flags |= ObjectStreamConstants.SC_BLOCK_DATA;

             }

         } else if (serializable) {

             flags |= ObjectStreamConstants.SC_SERIALIZABLE;

         }

         if (hasWriteObjectData) {

             flags |= ObjectStreamConstants.SC_WRITE_METHOD;

         }

         if (isEnum) {

             flags |= ObjectStreamConstants.SC_ENUM;

         }

         out.writeByte(flags);

         out.writeShort(fields.length);

         for (int i = 0; i < fields.length; i++) {

             ObjectStreamField f = fields[i];

             out.writeByte(f.getTypeCode());

             out.writeUTF(f.getName());

             if (!f.isPrimitive()) {

                 out.writeTypeString(f.getTypeString());

             }

         }

     }

     /**

      * Returns ClassNotFoundException (if any) thrown while attempting to

      * resolve local class corresponding to this class descriptor.

      */

     ClassNotFoundException getResolveException() {

         return resolveEx;

     }

     /**

      * Throws an InvalidClassException if object instances referencing this

      * class descriptor should not be allowed to deserialize.  This method does

      * not apply to deserialization of enum constants.

      */

     void checkDeserialize() throws InvalidClassException {

         if (deserializeEx != null) {

             InvalidClassException ice =

                 new InvalidClassException(deserializeEx.classname,

                                           deserializeEx.getMessage());

             ice.initCause(deserializeEx);

             throw ice;

         }

     }

     /**

      * Throws an InvalidClassException if objects whose class is represented by

      * this descriptor should not be allowed to serialize.  This method does

      * not apply to serialization of enum constants.

      */

     void checkSerialize() throws InvalidClassException {

         if (serializeEx != null) {

             InvalidClassException ice =

                 new InvalidClassException(serializeEx.classname,

                                           serializeEx.getMessage());

             ice.initCause(serializeEx);

             throw ice;

         }

     }

     /**

      * Throws an InvalidClassException if objects whose class is represented by

      * this descriptor should not be permitted to use default serialization

      * (e.g., if the class declares serializable fields that do not correspond

      * to actual fields, and hence must use the GetField API).  This method

      * does not apply to deserialization of enum constants.

      */

     void checkDefaultSerialize() throws InvalidClassException {

         if (defaultSerializeEx != null) {

             InvalidClassException ice =

                 new InvalidClassException(defaultSerializeEx.classname,

                                           defaultSerializeEx.getMessage());

             ice.initCause(defaultSerializeEx);

             throw ice;

         }

     }

     /**

      * Returns superclass descriptor.  Note that on the receiving side, the

      * superclass descriptor may be bound to a class that is not a superclass

      * of the subclass descriptor's bound class.

      */

     ObjectStreamClass getSuperDesc() {

         return superDesc;

     }

     /**

      * Returns the "local" class descriptor for the class associated with this

      * class descriptor (i.e., the result of

      * ObjectStreamClass.lookup(this.forClass())) or null if there is no class

      * associated with this descriptor.

      */

     ObjectStreamClass getLocalDesc() {

         return localDesc;

     }

     /**

      * Returns arrays of ObjectStreamFields representing the serializable

      * fields of the represented class.  If copy is true, a clone of this class

      * descriptor's field array is returned, otherwise the array itself is

      * returned.

      */

     ObjectStreamField[] getFields(boolean copy) {

         return copy ? fields.clone() : fields;

     }

     /**

      * Looks up a serializable field of the represented class by name and type.

      * A specified type of null matches all types, Object.class matches all

      * non-primitive types, and any other non-null type matches assignable

      * types only.  Returns matching field, or null if no match found.

      */

     ObjectStreamField getField(String name, Class<?> type) {

         for (int i = 0; i < fields.length; i++) {

             ObjectStreamField f = fields[i];

             if (f.getName().equals(name)) {

                 if (type == null ||

                     (type == Object.class && !f.isPrimitive()))

                 {

                     return f;

                 }

                 Class<?> ftype = f.getType();

                 if (ftype != null && type.isAssignableFrom(ftype)) {

                     return f;

                 }

             }

         }

         return null;

     }

     /**

      * Returns true if class descriptor represents a dynamic proxy class, false

      * otherwise.

      */

     boolean isProxy() {

         return isProxy;

     }

     /**

      * Returns true if class descriptor represents an enum type, false

      * otherwise.

      */

     boolean isEnum() {

         return isEnum;

     }

     /**

      * Returns true if represented class implements Externalizable, false

      * otherwise.

      */

     boolean isExternalizable() {

         return externalizable;

     }

     /**

      * Returns true if represented class implements Serializable, false

      * otherwise.

      */

     boolean isSerializable() {

         return serializable;

     }

     /**

      * Returns true if class descriptor represents externalizable class that

      * has written its data in 1.2 (block data) format, false otherwise.

      */

     boolean hasBlockExternalData() {

         return hasBlockExternalData;

     }

     /**

      * Returns true if class descriptor represents serializable (but not

      * externalizable) class which has written its data via a custom

      * writeObject() method, false otherwise.

      */

     boolean hasWriteObjectData() {

         return hasWriteObjectData;

     }

     /**

      * Returns true if represented class is serializable/externalizable and can

      * be instantiated by the serialization runtime--i.e., if it is

      * externalizable and defines a public no-arg constructor, or if it is

      * non-externalizable and its first non-serializable superclass defines an

      * accessible no-arg constructor.  Otherwise, returns false.

      */

     boolean isInstantiable() {

         return (cons != null);

     }

     /**

      * Returns true if represented class is serializable (but not

      * externalizable) and defines a conformant writeObject method.  Otherwise,

      * returns false.

      */

     boolean hasWriteObjectMethod() {

         return (writeObjectMethod != null);

     }

     /**

      * Returns true if represented class is serializable (but not

      * externalizable) and defines a conformant readObject method.  Otherwise,

      * returns false.

      */

     boolean hasReadObjectMethod() {

         return (readObjectMethod != null);

     }

     /**

      * Returns true if represented class is serializable (but not

      * externalizable) and defines a conformant readObjectNoData method.

      * Otherwise, returns false.

      */

     boolean hasReadObjectNoDataMethod() {

         return (readObjectNoDataMethod != null);

     }

     /**

      * Returns true if represented class is serializable or externalizable and

      * defines a conformant writeReplace method.  Otherwise, returns false.

      */

     boolean hasWriteReplaceMethod() {

         return (writeReplaceMethod != null);

     }

     /**

      * Returns true if represented class is serializable or externalizable and

      * defines a conformant readResolve method.  Otherwise, returns false.

      */

     boolean hasReadResolveMethod() {

         return (readResolveMethod != null);

     }

     /**

      * Creates a new instance of the represented class.  If the class is

      * externalizable, invokes its public no-arg constructor; otherwise, if the

      * class is serializable, invokes the no-arg constructor of the first

      * non-serializable superclass.  Throws UnsupportedOperationException if

      * this class descriptor is not associated with a class, if the associated

      * class is non-serializable or if the appropriate no-arg constructor is

      * inaccessible/unavailable.

      */

     Object newInstance()

         throws InstantiationException, InvocationTargetException,

                UnsupportedOperationException

     {

         if (cons != null) {

             try {

                 return cons.newInstance();

             } catch (IllegalAccessException ex) {

                 // should not occur, as access checks have been suppressed

                 throw new InternalError();

             }

         } else {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Invokes the writeObject method of the represented serializable class.

      * Throws UnsupportedOperationException if this class descriptor is not

      * associated with a class, or if the class is externalizable,

      * non-serializable or does not define writeObject.

      */

     void invokeWriteObject(Object obj, ObjectOutputStream out)

         throws IOException, UnsupportedOperationException

     {

         if (writeObjectMethod != null) {

             try {

                 writeObjectMethod.invoke(obj, new Object[]{ out });

             } catch (InvocationTargetException ex) {

                 Throwable th = ex.getTargetException();

                 if (th instanceof IOException) {

                     throw (IOException) th;

                 } else {

                     throwMiscException(th);

                 }

             } catch (IllegalAccessException ex) {

                 // should not occur, as access checks have been suppressed

                 throw new InternalError();

             }

         } else {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Invokes the readObject method of the represented serializable class.

      * Throws UnsupportedOperationException if this class descriptor is not

      * associated with a class, or if the class is externalizable,

      * non-serializable or does not define readObject.

      */

     void invokeReadObject(Object obj, ObjectInputStream in)

         throws ClassNotFoundException, IOException,

                UnsupportedOperationException

     {

         if (readObjectMethod != null) {

             try {

                 readObjectMethod.invoke(obj, new Object[]{ in });

             } catch (InvocationTargetException ex) {

                 Throwable th = ex.getTargetException();

                 if (th instanceof ClassNotFoundException) {

                     throw (ClassNotFoundException) th;

                 } else if (th instanceof IOException) {

                     throw (IOException) th;

                 } else {

                     throwMiscException(th);

                 }

             } catch (IllegalAccessException ex) {

                 // should not occur, as access checks have been suppressed

                 throw new InternalError();

             }

         } else {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Invokes the readObjectNoData method of the represented serializable

      * class.  Throws UnsupportedOperationException if this class descriptor is

      * not associated with a class, or if the class is externalizable,

      * non-serializable or does not define readObjectNoData.

      */

     void invokeReadObjectNoData(Object obj)

         throws IOException, UnsupportedOperationException

     {

         if (readObjectNoDataMethod != null) {

             try {

                 readObjectNoDataMethod.invoke(obj, (Object[]) null);

             } catch (InvocationTargetException ex) {

                 Throwable th = ex.getTargetException();

                 if (th instanceof ObjectStreamException) {

                     throw (ObjectStreamException) th;

                 } else {

                     throwMiscException(th);

                 }

             } catch (IllegalAccessException ex) {

                 // should not occur, as access checks have been suppressed

                 throw new InternalError();

             }

         } else {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Invokes the writeReplace method of the represented serializable class and

      * returns the result.  Throws UnsupportedOperationException if this class

      * descriptor is not associated with a class, or if the class is

      * non-serializable or does not define writeReplace.

      */

     Object invokeWriteReplace(Object obj)

         throws IOException, UnsupportedOperationException

     {

         if (writeReplaceMethod != null) {

             try {

                 return writeReplaceMethod.invoke(obj, (Object[]) null);

             } catch (InvocationTargetException ex) {

                 Throwable th = ex.getTargetException();

                 if (th instanceof ObjectStreamException) {

                     throw (ObjectStreamException) th;

                 } else {

                     throwMiscException(th);

                     throw new InternalError();  // never reached

                 }

             } catch (IllegalAccessException ex) {

                 // should not occur, as access checks have been suppressed

                 throw new InternalError();

             }

         } else {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Invokes the readResolve method of the represented serializable class and

      * returns the result.  Throws UnsupportedOperationException if this class

      * descriptor is not associated with a class, or if the class is

      * non-serializable or does not define readResolve.

      */

     Object invokeReadResolve(Object obj)

         throws IOException, UnsupportedOperationException

     {

         if (readResolveMethod != null) {

             try {

                 return readResolveMethod.invoke(obj, (Object[]) null);

             } catch (InvocationTargetException ex) {

                 Throwable th = ex.getTargetException();

                 if (th instanceof ObjectStreamException) {

                     throw (ObjectStreamException) th;

                 } else {

                     throwMiscException(th);

                     throw new InternalError();  // never reached

                 }

             } catch (IllegalAccessException ex) {

                 // should not occur, as access checks have been suppressed

                 throw new InternalError();

             }

         } else {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Class representing the portion of an object's serialized form allotted

      * to data described by a given class descriptor.  If "hasData" is false,

      * the object's serialized form does not contain data associated with the

      * class descriptor.

      */

     static class ClassDataSlot {

         /** class descriptor "occupying" this slot */

         final ObjectStreamClass desc;

         /** true if serialized form includes data for this slot's descriptor */

         final boolean hasData;

         ClassDataSlot(ObjectStreamClass desc, boolean hasData) {

             this.desc = desc;

             this.hasData = hasData;

         }

     }

     /**

      * Returns array of ClassDataSlot instances representing the data layout

      * (including superclass data) for serialized objects described by this

      * class descriptor.  ClassDataSlots are ordered by inheritance with those

      * containing "higher" superclasses appearing first.  The final

      * ClassDataSlot contains a reference to this descriptor.

      */

     ClassDataSlot[] getClassDataLayout() throws InvalidClassException {

         // REMIND: synchronize instead of relying on volatile?

         if (dataLayout == null) {

             dataLayout = getClassDataLayout0();

         }

         return dataLayout;

     }

     private ClassDataSlot[] getClassDataLayout0()

         throws InvalidClassException

     {

         ArrayList<ClassDataSlot> slots = new ArrayList<>();

         Class<?> start = cl, end = cl;

         // locate closest non-serializable superclass

         while (end != null && Serializable.class.isAssignableFrom(end)) {

             end = end.getSuperclass();

         }

         for (ObjectStreamClass d = this; d != null; d = d.superDesc) {

             // search up inheritance hierarchy for class with matching name

             String searchName = (d.cl != null) ? d.cl.getName() : d.name;

             Class<?> match = null;

             for (Class<?> c = start; c != end; c = c.getSuperclass()) {

                 if (searchName.equals(c.getName())) {

                     match = c;

                     break;

                 }

             }

             // add "no data" slot for each unmatched class below match

             if (match != null) {

                 for (Class<?> c = start; c != match; c = c.getSuperclass()) {

                     slots.add(new ClassDataSlot(

                         ObjectStreamClass.lookup(c, true), false));

                 }

                 start = match.getSuperclass();

             }

             // record descriptor/class pairing

             slots.add(new ClassDataSlot(d.getVariantFor(match), true));

         }

         // add "no data" slot for any leftover unmatched classes

         for (Class<?> c = start; c != end; c = c.getSuperclass()) {

             slots.add(new ClassDataSlot(

                 ObjectStreamClass.lookup(c, true), false));

         }

         // order slots from superclass -> subclass

         Collections.reverse(slots);

         return slots.toArray(new ClassDataSlot[slots.size()]);

     }

     /**

      * Returns aggregate size (in bytes) of marshalled primitive field values

      * for represented class.

      */

     int getPrimDataSize() {

         return primDataSize;

     }

     /**

      * Returns number of non-primitive serializable fields of represented

      * class.

      */

     int getNumObjFields() {

         return numObjFields;

     }

     /**

      * Fetches the serializable primitive field values of object obj and

      * marshals them into byte array buf starting at offset 0.  It is the

      * responsibility of the caller to ensure that obj is of the proper type if

      * non-null.

      */

     void getPrimFieldValues(Object obj, byte[] buf) {

         fieldRefl.getPrimFieldValues(obj, buf);

     }

     /**

      * Sets the serializable primitive fields of object obj using values

      * unmarshalled from byte array buf starting at offset 0.  It is the

      * responsibility of the caller to ensure that obj is of the proper type if

      * non-null.

      */

     void setPrimFieldValues(Object obj, byte[] buf) {

         fieldRefl.setPrimFieldValues(obj, buf);

     }

     /**

      * Fetches the serializable object field values of object obj and stores

      * them in array vals starting at offset 0.  It is the responsibility of

      * the caller to ensure that obj is of the proper type if non-null.

      */

     void getObjFieldValues(Object obj, Object[] vals) {

         fieldRefl.getObjFieldValues(obj, vals);

     }

     /**

      * Sets the serializable object fields of object obj using values from

      * array vals starting at offset 0.  It is the responsibility of the caller

      * to ensure that obj is of the proper type if non-null.

      */

     void setObjFieldValues(Object obj, Object[] vals) {

         fieldRefl.setObjFieldValues(obj, vals);

     }

     /**

      * Calculates and sets serializable field offsets, as well as primitive

      * data size and object field count totals.  Throws InvalidClassException

      * if fields are illegally ordered.

      */

     private void computeFieldOffsets() throws InvalidClassException {

         primDataSize = 0;

         numObjFields = 0;

         int firstObjIndex = -1;

         for (int i = 0; i < fields.length; i++) {

             ObjectStreamField f = fields[i];

             switch (f.getTypeCode()) {

                 case 'Z':

                 case 'B':

                     f.setOffset(primDataSize++);

                     break;

                 case 'C':

                 case 'S':

                     f.setOffset(primDataSize);

                     primDataSize += 2;

                     break;

                 case 'I':

                 case 'F':

                     f.setOffset(primDataSize);

                     primDataSize += 4;

                     break;

                 case 'J':

                 case 'D':

                     f.setOffset(primDataSize);

                     primDataSize += 8;

                     break;

                 case '[':

                 case 'L':

                     f.setOffset(numObjFields++);

                     if (firstObjIndex == -1) {

                         firstObjIndex = i;

                     }

                     break;

                 default:

                     throw new InternalError();

             }

         }

         if (firstObjIndex != -1 &&

             firstObjIndex + numObjFields != fields.length)

         {

             throw new InvalidClassException(name, "illegal field order");

         }

     }

     /**

      * If given class is the same as the class associated with this class

      * descriptor, returns reference to this class descriptor.  Otherwise,

      * returns variant of this class descriptor bound to given class.

      */

     private ObjectStreamClass getVariantFor(Class<?> cl)

         throws InvalidClassException

     {

         if (this.cl == cl) {

             return this;

         }

         ObjectStreamClass desc = new ObjectStreamClass();

         if (isProxy) {

             desc.initProxy(cl, null, superDesc);

         } else {

             desc.initNonProxy(this, cl, null, superDesc);

         }

         return desc;

     }

     /**

      * Returns public no-arg constructor of given class, or null if none found.

      * Access checks are disabled on the returned constructor (if any), since

      * the defining class may still be non-public.

      */

     private static Constructor getExternalizableConstructor(Class<?> cl) {

         try {

             Constructor cons = cl.getDeclaredConstructor((Class<?>[]) null);

             cons.setAccessible(true);

             return ((cons.getModifiers() & Modifier.PUBLIC) != 0) ?

                 cons : null;

         } catch (NoSuchMethodException ex) {

             return null;

         }

     }

     /**

      * Returns subclass-accessible no-arg constructor of first non-serializable

      * superclass, or null if none found.  Access checks are disabled on the

      * returned constructor (if any).

      */

     private static Constructor getSerializableConstructor(Class<?> cl) {

         Class<?> initCl = cl;

         while (Serializable.class.isAssignableFrom(initCl)) {

             if ((initCl = initCl.getSuperclass()) == null) {

                 return null;

             }

         }

         try {

             Constructor cons = initCl.getDeclaredConstructor((Class<?>[]) null);

             int mods = cons.getModifiers();

             if ((mods & Modifier.PRIVATE) != 0 ||

                 ((mods & (Modifier.PUBLIC | Modifier.PROTECTED)) == 0 &&

                  !packageEquals(cl, initCl)))

             {

                 return null;

             }

             cons = reflFactory.newConstructorForSerialization(cl, cons);

             cons.setAccessible(true);

             return cons;

         } catch (NoSuchMethodException ex) {

             return null;

         }

     }

     /**

      * Returns non-static, non-abstract method with given signature provided it

      * is defined by or accessible (via inheritance) by the given class, or

      * null if no match found.  Access checks are disabled on the returned

      * method (if any).

      */

     private static Method getInheritableMethod(Class<?> cl, String name,

                                                Class<?>[] argTypes,

                                                Class<?> returnType)

     {

         Method meth = null;

         Class<?> defCl = cl;

         while (defCl != null) {

             try {

                 meth = defCl.getDeclaredMethod(name, argTypes);

                 break;

             } catch (NoSuchMethodException ex) {

                 defCl = defCl.getSuperclass();

             }

         }

         if ((meth == null) || (meth.getReturnType() != returnType)) {

             return null;

         }

         meth.setAccessible(true);

         int mods = meth.getModifiers();

         if ((mods & (Modifier.STATIC | Modifier.ABSTRACT)) != 0) {

             return null;

         } else if ((mods & (Modifier.PUBLIC | Modifier.PROTECTED)) != 0) {

             return meth;

         } else if ((mods & Modifier.PRIVATE) != 0) {

             return (cl == defCl) ? meth : null;

         } else {

             return packageEquals(cl, defCl) ? meth : null;

         }

     }

     /**

      * Returns non-static private method with given signature defined by given

      * class, or null if none found.  Access checks are disabled on the

      * returned method (if any).

      */

     private static Method getPrivateMethod(Class<?> cl, String name,

                                            Class<?>[] argTypes,

                                            Class<?> returnType)

     {

         try {

             Method meth = cl.getDeclaredMethod(name, argTypes);

             meth.setAccessible(true);

             int mods = meth.getModifiers();

             return ((meth.getReturnType() == returnType) &&

                     ((mods & Modifier.STATIC) == 0) &&

                     ((mods & Modifier.PRIVATE) != 0)) ? meth : null;

         } catch (NoSuchMethodException ex) {

             return null;

         }

     }

     /**

      * Returns true if classes are defined in the same runtime package, false

      * otherwise.

      */

     private static boolean packageEquals(Class<?> cl1, Class<?> cl2) {

         return (cl1.getClassLoader() == cl2.getClassLoader() &&

                 getPackageName(cl1).equals(getPackageName(cl2)));

     }

     /**

      * Returns package name of given class.

      */

     private static String getPackageName(Class<?> cl) {

         String s = cl.getName();

         int i = s.lastIndexOf('[');

         if (i >= 0) {

             s = s.substring(i + 2);

         }

         i = s.lastIndexOf('.');

         return (i >= 0) ? s.substring(0, i) : "";

     }

     /**

      * Compares class names for equality, ignoring package names.  Returns true

      * if class names equal, false otherwise.

      */

     private static boolean classNamesEqual(String name1, String name2) {

         name1 = name1.substring(name1.lastIndexOf('.') + 1);

         name2 = name2.substring(name2.lastIndexOf('.') + 1);

         return name1.equals(name2);

     }

     /**

      * Returns JVM type signature for given class.

      */

     private static String getClassSignature(Class<?> cl) {

         StringBuilder sbuf = new StringBuilder();

         while (cl.isArray()) {

             sbuf.append('[');

             cl = cl.getComponentType();

         }

         if (cl.isPrimitive()) {

             if (cl == Integer.TYPE) {

                 sbuf.append('I');

             } else if (cl == Byte.TYPE) {

                 sbuf.append('B');

             } else if (cl == Long.TYPE) {

                 sbuf.append('J');

             } else if (cl == Float.TYPE) {

                 sbuf.append('F');

             } else if (cl == Double.TYPE) {

                 sbuf.append('D');

             } else if (cl == Short.TYPE) {

                 sbuf.append('S');

             } else if (cl == Character.TYPE) {

                 sbuf.append('C');

             } else if (cl == Boolean.TYPE) {

                 sbuf.append('Z');

             } else if (cl == Void.TYPE) {

                 sbuf.append('V');

             } else {

                 throw new InternalError();

             }

         } else {

             sbuf.append('L' + cl.getName().replace('.', '/') + ';');

         }

         return sbuf.toString();

     }

     /**

      * Returns JVM type signature for given list of parameters and return type.

      */

     private static String getMethodSignature(Class<?>[] paramTypes,

                                              Class<?> retType)

     {

         StringBuilder sbuf = new StringBuilder();

         sbuf.append('(');

         for (int i = 0; i < paramTypes.length; i++) {

             sbuf.append(getClassSignature(paramTypes[i]));

         }

         sbuf.append(')');

         sbuf.append(getClassSignature(retType));

         return sbuf.toString();

     }

     /**

      * Convenience method for throwing an exception that is either a

      * RuntimeException, Error, or of some unexpected type (in which case it is

      * wrapped inside an IOException).

      */

     private static void throwMiscException(Throwable th) throws IOException {

         if (th instanceof RuntimeException) {

             throw (RuntimeException) th;

         } else if (th instanceof Error) {

             throw (Error) th;

         } else {

             IOException ex = new IOException("unexpected exception type");

             ex.initCause(th);

             throw ex;

         }

     }

     /**

      * Returns ObjectStreamField array describing the serializable fields of

      * the given class.  Serializable fields backed by an actual field of the

      * class are represented by ObjectStreamFields with corresponding non-null

      * Field objects.  Throws InvalidClassException if the (explicitly

      * declared) serializable fields are invalid.

      */

     private static ObjectStreamField[] getSerialFields(Class<?> cl)

         throws InvalidClassException

     {

         ObjectStreamField[] fields;

         if (Serializable.class.isAssignableFrom(cl) &&

             !Externalizable.class.isAssignableFrom(cl) &&

             !Proxy.isProxyClass(cl) &&

             !cl.isInterface())

         {

             if ((fields = getDeclaredSerialFields(cl)) == null) {

                 fields = getDefaultSerialFields(cl);

             }

             Arrays.sort(fields);

         } else {

             fields = NO_FIELDS;

         }

         return fields;

     }

     /**

      * Returns serializable fields of given class as defined explicitly by a

      * "serialPersistentFields" field, or null if no appropriate

      * "serialPersistentFields" field is defined.  Serializable fields backed

      * by an actual field of the class are represented by ObjectStreamFields

      * with corresponding non-null Field objects.  For compatibility with past

      * releases, a "serialPersistentFields" field with a null value is

      * considered equivalent to not declaring "serialPersistentFields".  Throws

      * InvalidClassException if the declared serializable fields are

      * invalid--e.g., if multiple fields share the same name.

      */

     private static ObjectStreamField[] getDeclaredSerialFields(Class<?> cl)

         throws InvalidClassException

     {

         ObjectStreamField[] serialPersistentFields = null;

         try {

             Field f = cl.getDeclaredField("serialPersistentFields");

             int mask = Modifier.PRIVATE | Modifier.STATIC | Modifier.FINAL;

             if ((f.getModifiers() & mask) == mask) {

                 f.setAccessible(true);

                 serialPersistentFields = (ObjectStreamField[]) f.get(null);

             }

         } catch (Exception ex) {

         }

         if (serialPersistentFields == null) {

             return null;

         } else if (serialPersistentFields.length == 0) {

             return NO_FIELDS;

         }

         ObjectStreamField[] boundFields =

             new ObjectStreamField[serialPersistentFields.length];

         Set<String> fieldNames = new HashSet<>(serialPersistentFields.length);

         for (int i = 0; i < serialPersistentFields.length; i++) {

             ObjectStreamField spf = serialPersistentFields[i];

             String fname = spf.getName();

             if (fieldNames.contains(fname)) {

                 throw new InvalidClassException(

                     "multiple serializable fields named " + fname);

             }

             fieldNames.add(fname);

             try {

                 Field f = cl.getDeclaredField(fname);

                 if ((f.getType() == spf.getType()) &&

                     ((f.getModifiers() & Modifier.STATIC) == 0))

                 {

                     boundFields[i] =

                         new ObjectStreamField(f, spf.isUnshared(), true);

                 }

             } catch (NoSuchFieldException ex) {

             }

             if (boundFields[i] == null) {

                 boundFields[i] = new ObjectStreamField(

                     fname, spf.getType(), spf.isUnshared());

             }

         }

         return boundFields;

     }

     /**

      * Returns array of ObjectStreamFields corresponding to all non-static

      * non-transient fields declared by given class.  Each ObjectStreamField

      * contains a Field object for the field it represents.  If no default

      * serializable fields exist, NO_FIELDS is returned.

      */

     private static ObjectStreamField[] getDefaultSerialFields(Class<?> cl) {

         Field[] clFields = cl.getDeclaredFields();

         ArrayList<ObjectStreamField> list = new ArrayList<>();

         int mask = Modifier.STATIC | Modifier.TRANSIENT;

         for (int i = 0; i < clFields.length; i++) {

             if ((clFields[i].getModifiers() & mask) == 0) {

                 list.add(new ObjectStreamField(clFields[i], false, true));

             }

         }

         int size = list.size();

         return (size == 0) ? NO_FIELDS :

             list.toArray(new ObjectStreamField[size]);

     }

     /**

      * Returns explicit serial version UID value declared by given class, or

      * null if none.

      */

     private static Long getDeclaredSUID(Class<?> cl) {

         try {

             Field f = cl.getDeclaredField("serialVersionUID");

             int mask = Modifier.STATIC | Modifier.FINAL;

             if ((f.getModifiers() & mask) == mask) {

                 f.setAccessible(true);

                 return Long.valueOf(f.getLong(null));

             }

         } catch (Exception ex) {

         }

         return null;

     }

     /**

      * Computes the default serial version UID value for the given class.

      */

     private static long computeDefaultSUID(Class<?> cl) {

         if (!Serializable.class.isAssignableFrom(cl) || Proxy.isProxyClass(cl))

         {

             return 0L;

         }

         try {

             ByteArrayOutputStream bout = new ByteArrayOutputStream();

             DataOutputStream dout = new DataOutputStream(bout);

             dout.writeUTF(cl.getName());

             int classMods = cl.getModifiers() &

                 (Modifier.PUBLIC | Modifier.FINAL |

                  Modifier.INTERFACE | Modifier.ABSTRACT);

             /*

              * compensate for javac bug in which ABSTRACT bit was set for an

              * interface only if the interface declared methods

              */

             Method[] methods = cl.getDeclaredMethods();

             if ((classMods & Modifier.INTERFACE) != 0) {

                 classMods = (methods.length > 0) ?

                     (classMods | Modifier.ABSTRACT) :

                     (classMods & ~Modifier.ABSTRACT);

             }

             dout.writeInt(classMods);

             if (!cl.isArray()) {

                 /*

                  * compensate for change in 1.2FCS in which

                  * Class.getInterfaces() was modified to return Cloneable and

                  * Serializable for array classes.

                  */

                 Class<?>[] interfaces = cl.getInterfaces();

                 String[] ifaceNames = new String[interfaces.length];

                 for (int i = 0; i < interfaces.length; i++) {

                     ifaceNames[i] = interfaces[i].getName();

                 }

                 Arrays.sort(ifaceNames);

                 for (int i = 0; i < ifaceNames.length; i++) {

                     dout.writeUTF(ifaceNames[i]);

                 }

             }

             Field[] fields = cl.getDeclaredFields();

             MemberSignature[] fieldSigs = new MemberSignature[fields.length];

             for (int i = 0; i < fields.length; i++) {

                 fieldSigs[i] = new MemberSignature(fields[i]);

             }

             Arrays.sort(fieldSigs, new Comparator<MemberSignature>() {

                 public int compare(MemberSignature ms1, MemberSignature ms2) {

                     return ms1.name.compareTo(ms2.name);

                 }

             });

             for (int i = 0; i < fieldSigs.length; i++) {

                 MemberSignature sig = fieldSigs[i];

                 int mods = sig.member.getModifiers() &

                     (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |

                      Modifier.STATIC | Modifier.FINAL | Modifier.VOLATILE |

                      Modifier.TRANSIENT);

                 if (((mods & Modifier.PRIVATE) == 0) ||

                     ((mods & (Modifier.STATIC | Modifier.TRANSIENT)) == 0))

                 {

                     dout.writeUTF(sig.name);

                     dout.writeInt(mods);

                     dout.writeUTF(sig.signature);

                 }

             }

             if (hasStaticInitializer(cl)) {

                 dout.writeUTF("<clinit>");

                 dout.writeInt(Modifier.STATIC);

                 dout.writeUTF("()V");

             }

             Constructor[] cons = cl.getDeclaredConstructors();

             MemberSignature[] consSigs = new MemberSignature[cons.length];

             for (int i = 0; i < cons.length; i++) {

                 consSigs[i] = new MemberSignature(cons[i]);

             }

             Arrays.sort(consSigs, new Comparator<MemberSignature>() {

                 public int compare(MemberSignature ms1, MemberSignature ms2) {

                     return ms1.signature.compareTo(ms2.signature);

                 }

             });

             for (int i = 0; i < consSigs.length; i++) {

                 MemberSignature sig = consSigs[i];

                 int mods = sig.member.getModifiers() &

                     (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |

                      Modifier.STATIC | Modifier.FINAL |

                      Modifier.SYNCHRONIZED | Modifier.NATIVE |

                      Modifier.ABSTRACT | Modifier.STRICT);

                 if ((mods & Modifier.PRIVATE) == 0) {

                     dout.writeUTF("<init>");

                     dout.writeInt(mods);

                     dout.writeUTF(sig.signature.replace('/', '.'));

                 }

             }

             MemberSignature[] methSigs = new MemberSignature[methods.length];

             for (int i = 0; i < methods.length; i++) {

                 methSigs[i] = new MemberSignature(methods[i]);

             }

             Arrays.sort(methSigs, new Comparator<MemberSignature>() {

                 public int compare(MemberSignature ms1, MemberSignature ms2) {

                     int comp = ms1.name.compareTo(ms2.name);

                     if (comp == 0) {

                         comp = ms1.signature.compareTo(ms2.signature);

                     }

                     return comp;

                 }

             });

             for (int i = 0; i < methSigs.length; i++) {

                 MemberSignature sig = methSigs[i];

                 int mods = sig.member.getModifiers() &

                     (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |

                      Modifier.STATIC | Modifier.FINAL |

                      Modifier.SYNCHRONIZED | Modifier.NATIVE |

                      Modifier.ABSTRACT | Modifier.STRICT);

                 if ((mods & Modifier.PRIVATE) == 0) {

                     dout.writeUTF(sig.name);

                     dout.writeInt(mods);

                     dout.writeUTF(sig.signature.replace('/', '.'));

                 }

             }

             dout.flush();

             MessageDigest md = MessageDigest.getInstance("SHA");

             byte[] hashBytes = md.digest(bout.toByteArray());

             long hash = 0;

             for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {

                 hash = (hash << 8) | (hashBytes[i] & 0xFF);

             }

             return hash;

         } catch (IOException ex) {

             throw new InternalError();

         } catch (NoSuchAlgorithmException ex) {

             throw new SecurityException(ex.getMessage());

         }

     }

     /**

      * Returns true if the given class defines a static initializer method,

      * false otherwise.

      */

     private native static boolean hasStaticInitializer(Class<?> cl);

     /**

      * Class for computing and caching field/constructor/method signatures

      * during serialVersionUID calculation.

      */

     private static class MemberSignature {

         public final Member member;

         public final String name;

         public final String signature;

         public MemberSignature(Field field) {

             member = field;

             name = field.getName();

             signature = getClassSignature(field.getType());

         }

         public MemberSignature(Constructor cons) {

             member = cons;

             name = cons.getName();

             signature = getMethodSignature(

                 cons.getParameterTypes(), Void.TYPE);

         }

         public MemberSignature(Method meth) {

             member = meth;

             name = meth.getName();

             signature = getMethodSignature(

                 meth.getParameterTypes(), meth.getReturnType());

         }

     }

     /**

      * Class for setting and retrieving serializable field values in batch.

      */

     // REMIND: dynamically generate these?

     private static class FieldReflector {

         /** handle for performing unsafe operations */

         private static final Unsafe unsafe = Unsafe.getUnsafe();

         /** fields to operate on */

         private final ObjectStreamField[] fields;

         /** number of primitive fields */

         private final int numPrimFields;

         /** unsafe field keys for reading fields - may contain dupes */

         private final long[] readKeys;

         /** unsafe fields keys for writing fields - no dupes */

         private final long[] writeKeys;

         /** field data offsets */

         private final int[] offsets;

         /** field type codes */

         private final char[] typeCodes;

         /** field types */

         private final Class<?>[] types;

         /**

          * Constructs FieldReflector capable of setting/getting values from the

          * subset of fields whose ObjectStreamFields contain non-null

          * reflective Field objects.  ObjectStreamFields with null Fields are

          * treated as filler, for which get operations return default values

          * and set operations discard given values.

          */

         FieldReflector(ObjectStreamField[] fields) {

             this.fields = fields;

             int nfields = fields.length;

             readKeys = new long[nfields];

             writeKeys = new long[nfields];

             offsets = new int[nfields];

             typeCodes = new char[nfields];

             ArrayList<Class<?>> typeList = new ArrayList<>();

             Set<Long> usedKeys = new HashSet<>();

             for (int i = 0; i < nfields; i++) {

                 ObjectStreamField f = fields[i];

                 Field rf = f.getField();

                 long key = (rf != null) ?

                     unsafe.objectFieldOffset(rf) : Unsafe.INVALID_FIELD_OFFSET;

                 readKeys[i] = key;

                 writeKeys[i] = usedKeys.add(key) ?

                     key : Unsafe.INVALID_FIELD_OFFSET;

                 offsets[i] = f.getOffset();

                 typeCodes[i] = f.getTypeCode();

                 if (!f.isPrimitive()) {

                     typeList.add((rf != null) ? rf.getType() : null);

                 }

             }

             types = typeList.toArray(new Class<?>[typeList.size()]);

             numPrimFields = nfields - types.length;

         }

         /**

          * Returns list of ObjectStreamFields representing fields operated on

          * by this reflector.  The shared/unshared values and Field objects

          * contained by ObjectStreamFields in the list reflect their bindings

          * to locally defined serializable fields.

          */

         ObjectStreamField[] getFields() {

             return fields;

         }

         /**

          * Fetches the serializable primitive field values of object obj and

          * marshals them into byte array buf starting at offset 0.  The caller

          * is responsible for ensuring that obj is of the proper type.

          */

         void getPrimFieldValues(Object obj, byte[] buf) {

             if (obj == null) {

                 throw new NullPointerException();

             }

             /* assuming checkDefaultSerialize() has been called on the class

              * descriptor this FieldReflector was obtained from, no field keys

              * in array should be equal to Unsafe.INVALID_FIELD_OFFSET.

              */

             for (int i = 0; i < numPrimFields; i++) {

                 long key = readKeys[i];

                 int off = offsets[i];

                 switch (typeCodes[i]) {

                     case 'Z':

                         Bits.putBoolean(buf, off, unsafe.getBoolean(obj, key));

                         break;

                     case 'B':

                         buf[off] = unsafe.getByte(obj, key);

                         break;

                     case 'C':

                         Bits.putChar(buf, off, unsafe.getChar(obj, key));

                         break;

                     case 'S':

                         Bits.putShort(buf, off, unsafe.getShort(obj, key));

                         break;

                     case 'I':

                         Bits.putInt(buf, off, unsafe.getInt(obj, key));

                         break;

                     case 'F':

                         Bits.putFloat(buf, off, unsafe.getFloat(obj, key));

                         break;

                     case 'J':

                         Bits.putLong(buf, off, unsafe.getLong(obj, key));

                         break;

                     case 'D':

                         Bits.putDouble(buf, off, unsafe.getDouble(obj, key));

                         break;

                     default:

                         throw new InternalError();

                 }

             }

         }

         /**

          * Sets the serializable primitive fields of object obj using values

          * unmarshalled from byte array buf starting at offset 0.  The caller

          * is responsible for ensuring that obj is of the proper type.

          */

         void setPrimFieldValues(Object obj, byte[] buf) {

             if (obj == null) {

                 throw new NullPointerException();

             }

             for (int i = 0; i < numPrimFields; i++) {

                 long key = writeKeys[i];

                 if (key == Unsafe.INVALID_FIELD_OFFSET) {

                     continue;           // discard value

                 }

                 int off = offsets[i];

                 switch (typeCodes[i]) {

                     case 'Z':

                         unsafe.putBoolean(obj, key, Bits.getBoolean(buf, off));

                         break;

                     case 'B':

                         unsafe.putByte(obj, key, buf[off]);

                         break;

                     case 'C':

                         unsafe.putChar(obj, key, Bits.getChar(buf, off));

                         break;

                     case 'S':

                         unsafe.putShort(obj, key, Bits.getShort(buf, off));

                         break;

                     case 'I':

                         unsafe.putInt(obj, key, Bits.getInt(buf, off));

                         break;

                     case 'F':

                         unsafe.putFloat(obj, key, Bits.getFloat(buf, off));

                         break;

                     case 'J':

                         unsafe.putLong(obj, key, Bits.getLong(buf, off));

                         break;

                     case 'D':

                         unsafe.putDouble(obj, key, Bits.getDouble(buf, off));

                         break;

                     default:

                         throw new InternalError();

                 }

             }

         }

         /**

          * Fetches the serializable object field values of object obj and

          * stores them in array vals starting at offset 0.  The caller is

          * responsible for ensuring that obj is of the proper type.

          */

         void getObjFieldValues(Object obj, Object[] vals) {

             if (obj == null) {

                 throw new NullPointerException();

             }

             /* assuming checkDefaultSerialize() has been called on the class

              * descriptor this FieldReflector was obtained from, no field keys

              * in array should be equal to Unsafe.INVALID_FIELD_OFFSET.

              */

             for (int i = numPrimFields; i < fields.length; i++) {

                 switch (typeCodes[i]) {

                     case 'L':

                     case '[':

                         vals[offsets[i]] = unsafe.getObject(obj, readKeys[i]);

                         break;

                     default:

                         throw new InternalError();

                 }

             }

         }

         /**

          * Sets the serializable object fields of object obj using values from

          * array vals starting at offset 0.  The caller is responsible for

          * ensuring that obj is of the proper type; however, attempts to set a

          * field with a value of the wrong type will trigger an appropriate

          * ClassCastException.

          */

         void setObjFieldValues(Object obj, Object[] vals) {

             if (obj == null) {

                 throw new NullPointerException();

             }

             for (int i = numPrimFields; i < fields.length; i++) {

                 long key = writeKeys[i];

                 if (key == Unsafe.INVALID_FIELD_OFFSET) {

                     continue;           // discard value

                 }

                 switch (typeCodes[i]) {

                     case 'L':

                     case '[':

                         Object val = vals[offsets[i]];

                         if (val != null &&

                             !types[i - numPrimFields].isInstance(val))

                         {

                             Field f = fields[i].getField();

                             throw new ClassCastException(

                                 "cannot assign instance of " +

                                 val.getClass().getName() + " to field " +

                                 f.getDeclaringClass().getName() + "." +

                                 f.getName() + " of type " +

                                 f.getType().getName() + " in instance of " +

                                 obj.getClass().getName());

                         }

                         unsafe.putObject(obj, key, val);

                         break;

                     default:

                         throw new InternalError();

                 }

             }

         }

     }

     /**

      * Matches given set of serializable fields with serializable fields

      * described by the given local class descriptor, and returns a

      * FieldReflector instance capable of setting/getting values from the

      * subset of fields that match (non-matching fields are treated as filler,

      * for which get operations return default values and set operations

      * discard given values).  Throws InvalidClassException if unresolvable

      * type conflicts exist between the two sets of fields.

      */

     private static FieldReflector getReflector(ObjectStreamField[] fields,

                                                ObjectStreamClass localDesc)

         throws InvalidClassException

     {

         // class irrelevant if no fields

         Class<?> cl = (localDesc != null && fields.length > 0) ?

             localDesc.cl : null;

         processQueue(Caches.reflectorsQueue, Caches.reflectors);

         FieldReflectorKey key = new FieldReflectorKey(cl, fields,

                                                       Caches.reflectorsQueue);

         Reference<?> ref = Caches.reflectors.get(key);

         Object entry = null;

         if (ref != null) {

             entry = ref.get();

         }

         EntryFuture future = null;

         if (entry == null) {

             EntryFuture newEntry = new EntryFuture();

             Reference<?> newRef = new SoftReference<>(newEntry);

             do {

                 if (ref != null) {

                     Caches.reflectors.remove(key, ref);

                 }

                 ref = Caches.reflectors.putIfAbsent(key, newRef);

                 if (ref != null) {

                     entry = ref.get();

                 }

             } while (ref != null && entry == null);

             if (entry == null) {

                 future = newEntry;

             }

         }

         if (entry instanceof FieldReflector) {  // check common case first

             return (FieldReflector) entry;

         } else if (entry instanceof EntryFuture) {

             entry = ((EntryFuture) entry).get();

         } else if (entry == null) {

             try {

                 entry = new FieldReflector(matchFields(fields, localDesc));

             } catch (Throwable th) {

                 entry = th;

             }

             future.set(entry);

             Caches.reflectors.put(key, new SoftReference<Object>(entry));

         }

         if (entry instanceof FieldReflector) {

             return (FieldReflector) entry;

         } else if (entry instanceof InvalidClassException) {

             throw (InvalidClassException) entry;

         } else if (entry instanceof RuntimeException) {

             throw (RuntimeException) entry;

         } else if (entry instanceof Error) {

             throw (Error) entry;

         } else {

             throw new InternalError("unexpected entry: " + entry);

         }

     }

     /**

      * FieldReflector cache lookup key.  Keys are considered equal if they

      * refer to the same class and equivalent field formats.

      */

     private static class FieldReflectorKey extends WeakReference<Class<?>> {

         private final String sigs;

         private final int hash;

         private final boolean nullClass;

         FieldReflectorKey(Class<?> cl, ObjectStreamField[] fields,

                           ReferenceQueue<Class<?>> queue)

         {

             super(cl, queue);

             nullClass = (cl == null);

             StringBuilder sbuf = new StringBuilder();

             for (int i = 0; i < fields.length; i++) {

                 ObjectStreamField f = fields[i];

                 sbuf.append(f.getName()).append(f.getSignature());

             }

             sigs = sbuf.toString();

             hash = System.identityHashCode(cl) + sigs.hashCode();

         }

         public int hashCode() {

             return hash;

         }

         public boolean equals(Object obj) {

             if (obj == this) {

                 return true;

             }

             if (obj instanceof FieldReflectorKey) {

                 FieldReflectorKey other = (FieldReflectorKey) obj;

                 Class<?> referent;

                 return (nullClass ? other.nullClass

                                   : ((referent = get()) != null) &&

                                     (referent == other.get())) &&

                     sigs.equals(other.sigs);

             } else {

                 return false;

             }

         }

     }

     /**

      * Matches given set of serializable fields with serializable fields

      * obtained from the given local class descriptor (which contain bindings

      * to reflective Field objects).  Returns list of ObjectStreamFields in

      * which each ObjectStreamField whose signature matches that of a local

      * field contains a Field object for that field; unmatched

      * ObjectStreamFields contain null Field objects.  Shared/unshared settings

      * of the returned ObjectStreamFields also reflect those of matched local

      * ObjectStreamFields.  Throws InvalidClassException if unresolvable type

      * conflicts exist between the two sets of fields.

      */

     private static ObjectStreamField[] matchFields(ObjectStreamField[] fields,

                                                    ObjectStreamClass localDesc)

         throws InvalidClassException

     {

         ObjectStreamField[] localFields = (localDesc != null) ?

             localDesc.fields : NO_FIELDS;

         /*

          * Even if fields == localFields, we cannot simply return localFields

          * here.  In previous implementations of serialization,

          * ObjectStreamField.getType() returned Object.class if the

          * ObjectStreamField represented a non-primitive field and belonged to

          * a non-local class descriptor.  To preserve this (questionable)

          * behavior, the ObjectStreamField instances returned by matchFields

          * cannot report non-primitive types other than Object.class; hence

          * localFields cannot be returned directly.

          */

         ObjectStreamField[] matches = new ObjectStreamField[fields.length];

         for (int i = 0; i < fields.length; i++) {

             ObjectStreamField f = fields[i], m = null;

             for (int j = 0; j < localFields.length; j++) {

                 ObjectStreamField lf = localFields[j];

                 if (f.getName().equals(lf.getName())) {

                     if ((f.isPrimitive() || lf.isPrimitive()) &&

                         f.getTypeCode() != lf.getTypeCode())

                     {

                         throw new InvalidClassException(localDesc.name,

                             "incompatible types for field " + f.getName());

                     }

                     if (lf.getField() != null) {

                         m = new ObjectStreamField(

                             lf.getField(), lf.isUnshared(), false);

                     } else {

                         m = new ObjectStreamField(

                             lf.getName(), lf.getSignature(), lf.isUnshared());

                     }

                 }

             }

             if (m == null) {

                 m = new ObjectStreamField(

                     f.getName(), f.getSignature(), false);

             }

             m.setOffset(f.getOffset());

             matches[i] = m;

         }

         return matches;

     }

     /**

      * Removes from the specified map any keys that have been enqueued

      * on the specified reference queue.

      */

     static void processQueue(ReferenceQueue<Class<?>> queue,

                              ConcurrentMap<? extends

                              WeakReference<Class<?>>, ?> map)

     {

         Reference<? extends Class<?>> ref;

         while((ref = queue.poll()) != null) {

             map.remove(ref);

         }

     }

     /**

      *  Weak key for Class objects.

      *

      **/

     static class WeakClassKey extends WeakReference<Class<?>> {

         /**

          * saved value of the referent's identity hash code, to maintain

          * a consistent hash code after the referent has been cleared

          */

         private final int hash;

         /**

          * Create a new WeakClassKey to the given object, registered

          * with a queue.

          */

         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {

             super(cl, refQueue);

             hash = System.identityHashCode(cl);

         }

         /**

          * Returns the identity hash code of the original referent.

          */

         public int hashCode() {

             return hash;

         }

         /**

          * Returns true if the given object is this identical

          * WeakClassKey instance, or, if this object's referent has not

          * been cleared, if the given object is another WeakClassKey

          * instance with the identical non-null referent as this one.

          */

         public boolean equals(Object obj) {

             if (obj == this) {

                 return true;

             }

             if (obj instanceof WeakClassKey) {

                 Object referent = get();

                 return (referent != null) &&

                        (referent == ((WeakClassKey) obj).get());

             } else {

                 return false;

             }

         }

     }

 }