/*

 * 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.util.ArrayList;

import java.util.Arrays;

import java.util.Collections;

import java.util.Comparator;

import java.util.HashSet;

import java.util.Set;

/**

 * 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;

    /** 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) {

            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;

        }

        Object entry = null;

        EntryFuture future = null;

        if (entry == null) {

            EntryFuture newEntry = new EntryFuture();

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

            if (entry == null) {

                future = newEntry;

            }

        }

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

            return (ObjectStreamClass) entry;

        }

        if (entry instanceof EntryFuture) {

            future = (EntryFuture) entry;

            if (true) {

                /*

                 * 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;

            }

            // 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 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;

                }

            }

            return entry;

        }

    }

    /**

     * 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;

        suid = Long.valueOf(0);

        fields = NO_FIELDS;

        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;

        }

    }

    /**

     * 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;

            }

        }

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

        fields = null;

    }

    /**

     * 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