jdk-sandbox: comparison jdk/src/share/classes/java/io/ObjectOutputStream.java

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+/*
+* Copyright 1996-2006 Sun Microsystems, Inc.  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.  Sun designates this
+* particular file as subject to the "Classpath" exception as provided
+* by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+* CA 95054 USA or visit www.sun.com if you need additional information or
+* have any questions.
+*/
+package java.io;
+import java.io.ObjectStreamClass.WeakClassKey;
+import java.lang.ref.ReferenceQueue;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import static java.io.ObjectStreamClass.processQueue;
+/**
+* An ObjectOutputStream writes primitive data types and graphs of Java objects
+* to an OutputStream.  The objects can be read (reconstituted) using an
+* ObjectInputStream.  Persistent storage of objects can be accomplished by
+* using a file for the stream.  If the stream is a network socket stream, the
+* objects can be reconstituted on another host or in another process.
+*
+* <p>Only objects that support the java.io.Serializable interface can be
+* written to streams.  The class of each serializable object is encoded
+* including the class name and signature of the class, the values of the
+* object's fields and arrays, and the closure of any other objects referenced
+* from the initial objects.
+*
+* <p>The method writeObject is used to write an object to the stream.  Any
+* object, including Strings and arrays, is written with writeObject. Multiple
+* objects or primitives can be written to the stream.  The objects must be
+* read back from the corresponding ObjectInputstream with the same types and
+* in the same order as they were written.
+*
+* <p>Primitive data types can also be written to the stream using the
+* appropriate methods from DataOutput. Strings can also be written using the
+* writeUTF method.
+*
+* <p>The default serialization mechanism for an object writes the class of the
+* object, the class signature, and the values of all non-transient and
+* non-static fields.  References to other objects (except in transient or
+* static fields) cause those objects to be written also. Multiple references
+* to a single object are encoded using a reference sharing mechanism so that
+* graphs of objects can be restored to the same shape as when the original was
+* written.
+*
+* <p>For example to write an object that can be read by the example in
+* ObjectInputStream:
+* <br>
+* <pre>
+*      FileOutputStream fos = new FileOutputStream("t.tmp");
+*      ObjectOutputStream oos = new ObjectOutputStream(fos);
+*
+*      oos.writeInt(12345);
+*      oos.writeObject("Today");
+*      oos.writeObject(new Date());
+*
+*      oos.close();
+* </pre>
+*
+* <p>Classes that require special handling during the serialization and
+* deserialization process must implement special methods with these exact
+* signatures:
+* <br>
+* <pre>
+* private void readObject(java.io.ObjectInputStream stream)
+*     throws IOException, ClassNotFoundException;
+* private void writeObject(java.io.ObjectOutputStream stream)
+*     throws IOException
+* private void readObjectNoData()
+*     throws ObjectStreamException;
+* </pre>
+*
+* <p>The writeObject method is responsible for writing the state of the object
+* for its particular class so that the corresponding readObject method can
+* restore it.  The method does not need to concern itself with the state
+* belonging to the object's superclasses or subclasses.  State is saved by
+* writing the individual fields to the ObjectOutputStream using the
+* writeObject method or by using the methods for primitive data types
+* supported by DataOutput.
+*
+* <p>Serialization does not write out the fields of any object that does not
+* implement the java.io.Serializable interface.  Subclasses of Objects that
+* are not serializable can be serializable. In this case the non-serializable
+* class must have a no-arg constructor to allow its fields to be initialized.
+* In this case it is the responsibility of the subclass to save and restore
+* the state of the non-serializable class. It is frequently the case that the
+* fields of that class are accessible (public, package, or protected) or that
+* there are get and set methods that can be used to restore the state.
+*
+* <p>Serialization of an object can be prevented by implementing writeObject
+* and readObject methods that throw the NotSerializableException.  The
+* exception will be caught by the ObjectOutputStream and abort the
+* serialization process.
+*
+* <p>Implementing the Externalizable interface allows the object to assume
+* complete control over the contents and format of the object's serialized
+* form.  The methods of the Externalizable interface, writeExternal and
+* readExternal, are called to save and restore the objects state.  When
+* implemented by a class they can write and read their own state using all of
+* the methods of ObjectOutput and ObjectInput.  It is the responsibility of
+* the objects to handle any versioning that occurs.
+*
+* <p>Enum constants are serialized differently than ordinary serializable or
+* externalizable objects.  The serialized form of an enum constant consists
+* solely of its name; field values of the constant are not transmitted.  To
+* serialize an enum constant, ObjectOutputStream writes the string returned by
+* the constant's name method.  Like other serializable or externalizable
+* objects, enum constants can function as the targets of back references
+* appearing subsequently in the serialization stream.  The process by which
+* enum constants are serialized cannot be customized; any class-specific
+* writeObject and writeReplace methods defined by enum types are ignored
+* during serialization.  Similarly, any serialPersistentFields or
+* serialVersionUID field declarations are also ignored--all enum types have a
+* fixed serialVersionUID of 0L.
+*
+* <p>Primitive data, excluding serializable fields and externalizable data, is
+* written to the ObjectOutputStream in block-data records. A block data record
+* is composed of a header and data. The block data header consists of a marker
+* and the number of bytes to follow the header.  Consecutive primitive data
+* writes are merged into one block-data record.  The blocking factor used for
+* a block-data record will be 1024 bytes.  Each block-data record will be
+* filled up to 1024 bytes, or be written whenever there is a termination of
+* block-data mode.  Calls to the ObjectOutputStream methods writeObject,
+* defaultWriteObject and writeFields initially terminate any existing
+* block-data record.
+*
+* @author      Mike Warres
+* @author      Roger Riggs
+* @see java.io.DataOutput
+* @see java.io.ObjectInputStream
+* @see java.io.Serializable
+* @see java.io.Externalizable
+* @see <a href="../../../platform/serialization/spec/output.html">Object Serialization Specification, Section 2, Object Output Classes</a>
+* @since       JDK1.1
+*/
+public class ObjectOutputStream
+extends OutputStream implements ObjectOutput, ObjectStreamConstants
+{
+private static class Caches {
+/** cache of subclass security audit results */
+static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
+new ConcurrentHashMap<WeakClassKey,Boolean>();
+/** queue for WeakReferences to audited subclasses */
+static final ReferenceQueue<Class<?>> subclassAuditsQueue =
+new ReferenceQueue<Class<?>>();
+}
+/** filter stream for handling block data conversion */
+private final BlockDataOutputStream bout;
+/** obj -> wire handle map */
+private final HandleTable handles;
+/** obj -> replacement obj map */
+private final ReplaceTable subs;
+/** stream protocol version */
+private int protocol = PROTOCOL_VERSION_2;
+/** recursion depth */
+private int depth;
+/** buffer for writing primitive field values */
+private byte[] primVals;
+/** if true, invoke writeObjectOverride() instead of writeObject() */
+private final boolean enableOverride;
+/** if true, invoke replaceObject() */
+private boolean enableReplace;
+// values below valid only during upcalls to writeObject()/writeExternal()
+/** object currently being serialized */
+private Object curObj;
+/** descriptor for current class (null if in writeExternal()) */
+private ObjectStreamClass curDesc;
+/** current PutField object */
+private PutFieldImpl curPut;
+/** custom storage for debug trace info */
+private final DebugTraceInfoStack debugInfoStack;
+/**
+* value of "sun.io.serialization.extendedDebugInfo" property,
+* as true or false for extended information about exception's place
+*/
+private static final boolean extendedDebugInfo =
+java.security.AccessController.doPrivileged(
+new sun.security.action.GetBooleanAction(
+"sun.io.serialization.extendedDebugInfo")).booleanValue();
+/**
+* Creates an ObjectOutputStream that writes to the specified OutputStream.
+* This constructor writes the serialization stream header to the
+* underlying stream; callers may wish to flush the stream immediately to
+* ensure that constructors for receiving ObjectInputStreams will not block
+* when reading the header.
+*
+* <p>If a security manager is installed, this constructor will check for
+* the "enableSubclassImplementation" SerializablePermission when invoked
+* directly or indirectly by the constructor of a subclass which overrides
+* the ObjectOutputStream.putFields or ObjectOutputStream.writeUnshared
+* methods.
+*
+* @param   out output stream to write to
+* @throws  IOException if an I/O error occurs while writing stream header
+* @throws  SecurityException if untrusted subclass illegally overrides
+*          security-sensitive methods
+* @throws  NullPointerException if <code>out</code> is <code>null</code>
+* @since   1.4
+* @see     ObjectOutputStream#ObjectOutputStream()
+* @see     ObjectOutputStream#putFields()
+* @see     ObjectInputStream#ObjectInputStream(InputStream)
+*/
+public ObjectOutputStream(OutputStream out) throws IOException {
+verifySubclass();
+bout = new BlockDataOutputStream(out);
+handles = new HandleTable(10, (float) 3.00);
+subs = new ReplaceTable(10, (float) 3.00);
+enableOverride = false;
+writeStreamHeader();
+bout.setBlockDataMode(true);
+if (extendedDebugInfo) {
+debugInfoStack = new DebugTraceInfoStack();
+} else {
+debugInfoStack = null;
+}
+}
+/**
+* Provide a way for subclasses that are completely reimplementing
+* ObjectOutputStream to not have to allocate private data just used by
+* this implementation of ObjectOutputStream.
+*
+* <p>If there is a security manager installed, this method first calls the
+* security manager's <code>checkPermission</code> method with a
+* <code>SerializablePermission("enableSubclassImplementation")</code>
+* permission to ensure it's ok to enable subclassing.
+*
+* @throws  SecurityException if a security manager exists and its
+*          <code>checkPermission</code> method denies enabling
+*          subclassing.
+* @see SecurityManager#checkPermission
+* @see java.io.SerializablePermission
+*/
+protected ObjectOutputStream() throws IOException, SecurityException {
+SecurityManager sm = System.getSecurityManager();
+if (sm != null) {
+sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
+}
+bout = null;
+handles = null;
+subs = null;
+enableOverride = true;
+debugInfoStack = null;
+}
+/**
+* Specify stream protocol version to use when writing the stream.
+*
+* <p>This routine provides a hook to enable the current version of
+* Serialization to write in a format that is backwards compatible to a
+* previous version of the stream format.
+*
+* <p>Every effort will be made to avoid introducing additional
+* backwards incompatibilities; however, sometimes there is no
+* other alternative.
+*
+* @param   version use ProtocolVersion from java.io.ObjectStreamConstants.
+* @throws  IllegalStateException if called after any objects
+*          have been serialized.
+* @throws  IllegalArgumentException if invalid version is passed in.
+* @throws  IOException if I/O errors occur
+* @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
+* @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_2
+* @since   1.2
+*/
+public void useProtocolVersion(int version) throws IOException {
+if (handles.size() != 0) {
+// REMIND: implement better check for pristine stream?
+throw new IllegalStateException("stream non-empty");
+}
+switch (version) {
+case PROTOCOL_VERSION_1:
+case PROTOCOL_VERSION_2:
+protocol = version;
+break;
+default:
+throw new IllegalArgumentException(
+"unknown version: " + version);
+}
+}
+/**
+* Write the specified object to the ObjectOutputStream.  The class of the
+* object, the signature of the class, and the values of the non-transient
+* and non-static fields of the class and all of its supertypes are
+* written.  Default serialization for a class can be overridden using the
+* writeObject and the readObject methods.  Objects referenced by this
+* object are written transitively so that a complete equivalent graph of
+* objects can be reconstructed by an ObjectInputStream.
+*
+* <p>Exceptions are thrown for problems with the OutputStream and for
+* classes that should not be serialized.  All exceptions are fatal to the
+* OutputStream, which is left in an indeterminate state, and it is up to
+* the caller to ignore or recover the stream state.
+*
+* @throws  InvalidClassException Something is wrong with a class used by
+*          serialization.
+* @throws  NotSerializableException Some object to be serialized does not
+*          implement the java.io.Serializable interface.
+* @throws  IOException Any exception thrown by the underlying
+*          OutputStream.
+*/
+public final void writeObject(Object obj) throws IOException {
+if (enableOverride) {
+writeObjectOverride(obj);
+return;
+}
+try {
+writeObject0(obj, false);
+} catch (IOException ex) {
+if (depth == 0) {
+writeFatalException(ex);
+}
+throw ex;
+}
+}
+/**
+* Method used by subclasses to override the default writeObject method.
+* This method is called by trusted subclasses of ObjectInputStream that
+* constructed ObjectInputStream using the protected no-arg constructor.
+* The subclass is expected to provide an override method with the modifier
+* "final".
+*
+* @param   obj object to be written to the underlying stream
+* @throws  IOException if there are I/O errors while writing to the
+*          underlying stream
+* @see #ObjectOutputStream()
+* @see #writeObject(Object)
+* @since 1.2
+*/
+protected void writeObjectOverride(Object obj) throws IOException {
+}
+/**
+* Writes an "unshared" object to the ObjectOutputStream.  This method is
+* identical to writeObject, except that it always writes the given object
+* as a new, unique object in the stream (as opposed to a back-reference
+* pointing to a previously serialized instance).  Specifically:
+* <ul>
+*   <li>An object written via writeUnshared is always serialized in the
+*       same manner as a newly appearing object (an object that has not
+*       been written to the stream yet), regardless of whether or not the
+*       object has been written previously.
+*
+*   <li>If writeObject is used to write an object that has been previously
+*       written with writeUnshared, the previous writeUnshared operation
+*       is treated as if it were a write of a separate object.  In other
+*       words, ObjectOutputStream will never generate back-references to
+*       object data written by calls to writeUnshared.
+* </ul>
+* While writing an object via writeUnshared does not in itself guarantee a
+* unique reference to the object when it is deserialized, it allows a
+* single object to be defined multiple times in a stream, so that multiple
+* calls to readUnshared by the receiver will not conflict.  Note that the
+* rules described above only apply to the base-level object written with
+* writeUnshared, and not to any transitively referenced sub-objects in the
+* object graph to be serialized.
+*
+* <p>ObjectOutputStream subclasses which override this method can only be
+* constructed in security contexts possessing the
+* "enableSubclassImplementation" SerializablePermission; any attempt to
+* instantiate such a subclass without this permission will cause a
+* SecurityException to be thrown.
+*
+* @param   obj object to write to stream
+* @throws  NotSerializableException if an object in the graph to be
+*          serialized does not implement the Serializable interface
+* @throws  InvalidClassException if a problem exists with the class of an
+*          object to be serialized
+* @throws  IOException if an I/O error occurs during serialization
+* @since 1.4
+*/
+public void writeUnshared(Object obj) throws IOException {
+try {
+writeObject0(obj, true);
+} catch (IOException ex) {
+if (depth == 0) {
+writeFatalException(ex);
+}
+throw ex;
+}
+}
+/**
+* Write the non-static and non-transient fields of the current class to
+* this stream.  This may only be called from the writeObject method of the
+* class being serialized. It will throw the NotActiveException if it is
+* called otherwise.
+*
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          <code>OutputStream</code>
+*/
+public void defaultWriteObject() throws IOException {
+if (curObj == null || curDesc == null) {
+throw new NotActiveException("not in call to writeObject");
+}
+bout.setBlockDataMode(false);
+defaultWriteFields(curObj, curDesc);
+bout.setBlockDataMode(true);
+}
+/**
+* Retrieve the object used to buffer persistent fields to be written to
+* the stream.  The fields will be written to the stream when writeFields
+* method is called.
+*
+* @return  an instance of the class Putfield that holds the serializable
+*          fields
+* @throws  IOException if I/O errors occur
+* @since 1.2
+*/
+public ObjectOutputStream.PutField putFields() throws IOException {
+if (curPut == null) {
+if (curObj == null || curDesc == null) {
+throw new NotActiveException("not in call to writeObject");
+}
+curPut = new PutFieldImpl(curDesc);
+}
+return curPut;
+}
+/**
+* Write the buffered fields to the stream.
+*
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+* @throws  NotActiveException Called when a classes writeObject method was
+*          not called to write the state of the object.
+* @since 1.2
+*/
+public void writeFields() throws IOException {
+if (curPut == null) {
+throw new NotActiveException("no current PutField object");
+}
+bout.setBlockDataMode(false);
+curPut.writeFields();
+bout.setBlockDataMode(true);
+}
+/**
+* Reset will disregard the state of any objects already written to the
+* stream.  The state is reset to be the same as a new ObjectOutputStream.
+* The current point in the stream is marked as reset so the corresponding
+* ObjectInputStream will be reset at the same point.  Objects previously
+* written to the stream will not be refered to as already being in the
+* stream.  They will be written to the stream again.
+*
+* @throws  IOException if reset() is invoked while serializing an object.
+*/
+public void reset() throws IOException {
+if (depth != 0) {
+throw new IOException("stream active");
+}
+bout.setBlockDataMode(false);
+bout.writeByte(TC_RESET);
+clear();
+bout.setBlockDataMode(true);
+}
+/**
+* Subclasses may implement this method to allow class data to be stored in
+* the stream. By default this method does nothing.  The corresponding
+* method in ObjectInputStream is resolveClass.  This method is called
+* exactly once for each unique class in the stream.  The class name and
+* signature will have already been written to the stream.  This method may
+* make free use of the ObjectOutputStream to save any representation of
+* the class it deems suitable (for example, the bytes of the class file).
+* The resolveClass method in the corresponding subclass of
+* ObjectInputStream must read and use any data or objects written by
+* annotateClass.
+*
+* @param   cl the class to annotate custom data for
+* @throws  IOException Any exception thrown by the underlying
+*          OutputStream.
+*/
+protected void annotateClass(Class<?> cl) throws IOException {
+}
+/**
+* Subclasses may implement this method to store custom data in the stream
+* along with descriptors for dynamic proxy classes.
+*
+* <p>This method is called exactly once for each unique proxy class
+* descriptor in the stream.  The default implementation of this method in
+* <code>ObjectOutputStream</code> does nothing.
+*
+* <p>The corresponding method in <code>ObjectInputStream</code> is
+* <code>resolveProxyClass</code>.  For a given subclass of
+* <code>ObjectOutputStream</code> that overrides this method, the
+* <code>resolveProxyClass</code> method in the corresponding subclass of
+* <code>ObjectInputStream</code> must read any data or objects written by
+* <code>annotateProxyClass</code>.
+*
+* @param   cl the proxy class to annotate custom data for
+* @throws  IOException any exception thrown by the underlying
+*          <code>OutputStream</code>
+* @see ObjectInputStream#resolveProxyClass(String[])
+* @since   1.3
+*/
+protected void annotateProxyClass(Class<?> cl) throws IOException {
+}
+/**
+* This method will allow trusted subclasses of ObjectOutputStream to
+* substitute one object for another during serialization. Replacing
+* objects is disabled until enableReplaceObject is called. The
+* enableReplaceObject method checks that the stream requesting to do
+* replacement can be trusted.  The first occurrence of each object written
+* into the serialization stream is passed to replaceObject.  Subsequent
+* references to the object are replaced by the object returned by the
+* original call to replaceObject.  To ensure that the private state of
+* objects is not unintentionally exposed, only trusted streams may use
+* replaceObject.
+*
+* <p>The ObjectOutputStream.writeObject method takes a parameter of type
+* Object (as opposed to type Serializable) to allow for cases where
+* non-serializable objects are replaced by serializable ones.
+*
+* <p>When a subclass is replacing objects it must insure that either a
+* complementary substitution must be made during deserialization or that
+* the substituted object is compatible with every field where the
+* reference will be stored.  Objects whose type is not a subclass of the
+* type of the field or array element abort the serialization by raising an
+* exception and the object is not be stored.
+*
+* <p>This method is called only once when each object is first
+* encountered.  All subsequent references to the object will be redirected
+* to the new object. This method should return the object to be
+* substituted or the original object.
+*
+* <p>Null can be returned as the object to be substituted, but may cause
+* NullReferenceException in classes that contain references to the
+* original object since they may be expecting an object instead of
+* null.
+*
+* @param   obj the object to be replaced
+* @return  the alternate object that replaced the specified one
+* @throws  IOException Any exception thrown by the underlying
+*          OutputStream.
+*/
+protected Object replaceObject(Object obj) throws IOException {
+return obj;
+}
+/**
+* Enable the stream to do replacement of objects in the stream.  When
+* enabled, the replaceObject method is called for every object being
+* serialized.
+*
+* <p>If <code>enable</code> is true, and there is a security manager
+* installed, this method first calls the security manager's
+* <code>checkPermission</code> method with a
+* <code>SerializablePermission("enableSubstitution")</code> permission to
+* ensure it's ok to enable the stream to do replacement of objects in the
+* stream.
+*
+* @param   enable boolean parameter to enable replacement of objects
+* @return  the previous setting before this method was invoked
+* @throws  SecurityException if a security manager exists and its
+*          <code>checkPermission</code> method denies enabling the stream
+*          to do replacement of objects in the stream.
+* @see SecurityManager#checkPermission
+* @see java.io.SerializablePermission
+*/
+protected boolean enableReplaceObject(boolean enable)
+throws SecurityException
+{
+if (enable == enableReplace) {
+return enable;
+}
+if (enable) {
+SecurityManager sm = System.getSecurityManager();
+if (sm != null) {
+sm.checkPermission(SUBSTITUTION_PERMISSION);
+}
+}
+enableReplace = enable;
+return !enableReplace;
+}
+/**
+* The writeStreamHeader method is provided so subclasses can append or
+* prepend their own header to the stream.  It writes the magic number and
+* version to the stream.
+*
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+protected void writeStreamHeader() throws IOException {
+bout.writeShort(STREAM_MAGIC);
+bout.writeShort(STREAM_VERSION);
+}
+/**
+* Write the specified class descriptor to the ObjectOutputStream.  Class
+* descriptors are used to identify the classes of objects written to the
+* stream.  Subclasses of ObjectOutputStream may override this method to
+* customize the way in which class descriptors are written to the
+* serialization stream.  The corresponding method in ObjectInputStream,
+* <code>readClassDescriptor</code>, should then be overridden to
+* reconstitute the class descriptor from its custom stream representation.
+* By default, this method writes class descriptors according to the format
+* defined in the Object Serialization specification.
+*
+* <p>Note that this method will only be called if the ObjectOutputStream
+* is not using the old serialization stream format (set by calling
+* ObjectOutputStream's <code>useProtocolVersion</code> method).  If this
+* serialization stream is using the old format
+* (<code>PROTOCOL_VERSION_1</code>), the class descriptor will be written
+* internally in a manner that cannot be overridden or customized.
+*
+* @param   desc class descriptor to write to the stream
+* @throws  IOException If an I/O error has occurred.
+* @see java.io.ObjectInputStream#readClassDescriptor()
+* @see #useProtocolVersion(int)
+* @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
+* @since 1.3
+*/
+protected void writeClassDescriptor(ObjectStreamClass desc)
+throws IOException
+{
+desc.writeNonProxy(this);
+}
+/**
+* Writes a byte. This method will block until the byte is actually
+* written.
+*
+* @param   val the byte to be written to the stream
+* @throws  IOException If an I/O error has occurred.
+*/
+public void write(int val) throws IOException {
+bout.write(val);
+}
+/**
+* Writes an array of bytes. This method will block until the bytes are
+* actually written.
+*
+* @param   buf the data to be written
+* @throws  IOException If an I/O error has occurred.
+*/
+public void write(byte[] buf) throws IOException {
+bout.write(buf, 0, buf.length, false);
+}
+/**
+* Writes a sub array of bytes.
+*
+* @param   buf the data to be written
+* @param   off the start offset in the data
+* @param   len the number of bytes that are written
+* @throws  IOException If an I/O error has occurred.
+*/
+public void write(byte[] buf, int off, int len) throws IOException {
+if (buf == null) {
+throw new NullPointerException();
+}
+int endoff = off + len;
+if (off < 0 || len < 0 || endoff > buf.length || endoff < 0) {
+throw new IndexOutOfBoundsException();
+}
+bout.write(buf, off, len, false);
+}
+/**
+* Flushes the stream. This will write any buffered output bytes and flush
+* through to the underlying stream.
+*
+* @throws  IOException If an I/O error has occurred.
+*/
+public void flush() throws IOException {
+bout.flush();
+}
+/**
+* Drain any buffered data in ObjectOutputStream.  Similar to flush but
+* does not propagate the flush to the underlying stream.
+*
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+protected void drain() throws IOException {
+bout.drain();
+}
+/**
+* Closes the stream. This method must be called to release any resources
+* associated with the stream.
+*
+* @throws  IOException If an I/O error has occurred.
+*/
+public void close() throws IOException {
+flush();
+clear();
+bout.close();
+}
+/**
+* Writes a boolean.
+*
+* @param   val the boolean to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeBoolean(boolean val) throws IOException {
+bout.writeBoolean(val);
+}
+/**
+* Writes an 8 bit byte.
+*
+* @param   val the byte value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeByte(int val) throws IOException  {
+bout.writeByte(val);
+}
+/**
+* Writes a 16 bit short.
+*
+* @param   val the short value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeShort(int val)  throws IOException {
+bout.writeShort(val);
+}
+/**
+* Writes a 16 bit char.
+*
+* @param   val the char value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeChar(int val)  throws IOException {
+bout.writeChar(val);
+}
+/**
+* Writes a 32 bit int.
+*
+* @param   val the integer value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeInt(int val)  throws IOException {
+bout.writeInt(val);
+}
+/**
+* Writes a 64 bit long.
+*
+* @param   val the long value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeLong(long val)  throws IOException {
+bout.writeLong(val);
+}
+/**
+* Writes a 32 bit float.
+*
+* @param   val the float value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeFloat(float val) throws IOException {
+bout.writeFloat(val);
+}
+/**
+* Writes a 64 bit double.
+*
+* @param   val the double value to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeDouble(double val) throws IOException {
+bout.writeDouble(val);
+}
+/**
+* Writes a String as a sequence of bytes.
+*
+* @param   str the String of bytes to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeBytes(String str) throws IOException {
+bout.writeBytes(str);
+}
+/**
+* Writes a String as a sequence of chars.
+*
+* @param   str the String of chars to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeChars(String str) throws IOException {
+bout.writeChars(str);
+}
+/**
+* Primitive data write of this String in
+* <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
+* format.  Note that there is a
+* significant difference between writing a String into the stream as
+* primitive data or as an Object. A String instance written by writeObject
+* is written into the stream as a String initially. Future writeObject()
+* calls write references to the string into the stream.
+*
+* @param   str the String to be written
+* @throws  IOException if I/O errors occur while writing to the underlying
+*          stream
+*/
+public void writeUTF(String str) throws IOException {
+bout.writeUTF(str);
+}
+/**
+* Provide programmatic access to the persistent fields to be written
+* to ObjectOutput.
+*
+* @since 1.2
+*/
+public static abstract class PutField {
+/**
+* Put the value of the named boolean field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>boolean</code>
+*/
+public abstract void put(String name, boolean val);
+/**
+* Put the value of the named byte field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>byte</code>
+*/
+public abstract void put(String name, byte val);
+/**
+* Put the value of the named char field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>char</code>
+*/
+public abstract void put(String name, char val);
+/**
+* Put the value of the named short field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>short</code>
+*/
+public abstract void put(String name, short val);
+/**
+* Put the value of the named int field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>int</code>
+*/
+public abstract void put(String name, int val);
+/**
+* Put the value of the named long field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>long</code>
+*/
+public abstract void put(String name, long val);
+/**
+* Put the value of the named float field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>float</code>
+*/
+public abstract void put(String name, float val);
+/**
+* Put the value of the named double field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not
+* <code>double</code>
+*/
+public abstract void put(String name, double val);
+/**
+* Put the value of the named Object field into the persistent field.
+*
+* @param  name the name of the serializable field
+* @param  val the value to assign to the field
+*         (which may be <code>null</code>)
+* @throws IllegalArgumentException if <code>name</code> does not
+* match the name of a serializable field for the class whose fields
+* are being written, or if the type of the named field is not a
+* reference type
+*/
+public abstract void put(String name, Object val);
+/**
+* Write the data and fields to the specified ObjectOutput stream,
+* which must be the same stream that produced this
+* <code>PutField</code> object.
+*
+* @param  out the stream to write the data and fields to
+* @throws IOException if I/O errors occur while writing to the
+*         underlying stream
+* @throws IllegalArgumentException if the specified stream is not
+*         the same stream that produced this <code>PutField</code>
+*         object
+* @deprecated This method does not write the values contained by this
+*         <code>PutField</code> object in a proper format, and may
+*         result in corruption of the serialization stream.  The
+*         correct way to write <code>PutField</code> data is by
+*         calling the {@link java.io.ObjectOutputStream#writeFields()}
+*         method.
+*/
+@Deprecated
+public abstract void write(ObjectOutput out) throws IOException;
+}
+/**
+* Returns protocol version in use.
+*/
+int getProtocolVersion() {
+return protocol;
+}
+/**
+* Writes string without allowing it to be replaced in stream.  Used by
+* ObjectStreamClass to write class descriptor type strings.
+*/
+void writeTypeString(String str) throws IOException {
+int handle;
+if (str == null) {
+writeNull();
+} else if ((handle = handles.lookup(str)) != -1) {
+writeHandle(handle);
+} else {
+writeString(str, false);
+}
+}
+/**
+* Verifies that this (possibly subclass) instance can be constructed
+* without violating security constraints: the subclass must not override
+* security-sensitive non-final methods, or else the
+* "enableSubclassImplementation" SerializablePermission is checked.
+*/
+private void verifySubclass() {
+Class cl = getClass();
+if (cl == ObjectOutputStream.class) {
+return;
+}
+SecurityManager sm = System.getSecurityManager();
+if (sm == null) {
+return;
+}
+processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
+WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
+Boolean result = Caches.subclassAudits.get(key);
+if (result == null) {
+result = Boolean.valueOf(auditSubclass(cl));
+Caches.subclassAudits.putIfAbsent(key, result);
+}
+if (result.booleanValue()) {
+return;
+}
+sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
+}
+/**
+* Performs reflective checks on given subclass to verify that it doesn't
+* override security-sensitive non-final methods.  Returns true if subclass
+* is "safe", false otherwise.
+*/
+private static boolean auditSubclass(final Class subcl) {
+Boolean result = AccessController.doPrivileged(
+new PrivilegedAction<Boolean>() {
+public Boolean run() {
+for (Class cl = subcl;
+cl != ObjectOutputStream.class;
+cl = cl.getSuperclass())
+{
+try {
+cl.getDeclaredMethod(
+"writeUnshared", new Class[] { Object.class });
+return Boolean.FALSE;
+} catch (NoSuchMethodException ex) {
+}
+try {
+cl.getDeclaredMethod("putFields", (Class[]) null);
+return Boolean.FALSE;
+} catch (NoSuchMethodException ex) {
+}
+}
+return Boolean.TRUE;
+}
+}
+);
+return result.booleanValue();
+}
+/**
+* Clears internal data structures.
+*/
+private void clear() {
+subs.clear();
+handles.clear();
+}
+/**
+* Underlying writeObject/writeUnshared implementation.
+*/
+private void writeObject0(Object obj, boolean unshared)
+throws IOException
+{
+boolean oldMode = bout.setBlockDataMode(false);
+depth++;
+try {
+// handle previously written and non-replaceable objects
+int h;
+if ((obj = subs.lookup(obj)) == null) {
+writeNull();
+return;
+} else if (!unshared && (h = handles.lookup(obj)) != -1) {
+writeHandle(h);
+return;
+} else if (obj instanceof Class) {
+writeClass((Class) obj, unshared);
+return;
+} else if (obj instanceof ObjectStreamClass) {
+writeClassDesc((ObjectStreamClass) obj, unshared);
+return;
+}
+// check for replacement object
+Object orig = obj;
+Class cl = obj.getClass();
+ObjectStreamClass desc;
+for (;;) {
+// REMIND: skip this check for strings/arrays?
+Class repCl;
+desc = ObjectStreamClass.lookup(cl, true);
+if (!desc.hasWriteReplaceMethod() ||
+(obj = desc.invokeWriteReplace(obj)) == null ||
+(repCl = obj.getClass()) == cl)
+{
+break;
+}
+cl = repCl;
+}
+if (enableReplace) {
+Object rep = replaceObject(obj);
+if (rep != obj && rep != null) {
+cl = rep.getClass();
+desc = ObjectStreamClass.lookup(cl, true);
+}
+obj = rep;
+}
+// if object replaced, run through original checks a second time
+if (obj != orig) {
+subs.assign(orig, obj);
+if (obj == null) {
+writeNull();
+return;
+} else if (!unshared && (h = handles.lookup(obj)) != -1) {
+writeHandle(h);
+return;
+} else if (obj instanceof Class) {
+writeClass((Class) obj, unshared);
+return;
+} else if (obj instanceof ObjectStreamClass) {
+writeClassDesc((ObjectStreamClass) obj, unshared);
+return;
+}
+}
+// remaining cases
+if (obj instanceof String) {
+writeString((String) obj, unshared);
+} else if (cl.isArray()) {
+writeArray(obj, desc, unshared);
+} else if (obj instanceof Enum) {
+writeEnum((Enum) obj, desc, unshared);
+} else if (obj instanceof Serializable) {
+writeOrdinaryObject(obj, desc, unshared);
+} else {
+if (extendedDebugInfo) {
+throw new NotSerializableException(
+cl.getName() + "\n" + debugInfoStack.toString());
+} else {
+throw new NotSerializableException(cl.getName());
+}
+}
+} finally {
+depth--;
+bout.setBlockDataMode(oldMode);
+}
+}
+/**
+* Writes null code to stream.
+*/
+private void writeNull() throws IOException {
+bout.writeByte(TC_NULL);
+}
+/**
+* Writes given object handle to stream.
+*/
+private void writeHandle(int handle) throws IOException {
+bout.writeByte(TC_REFERENCE);
+bout.writeInt(baseWireHandle + handle);
+}
+/**
+* Writes representation of given class to stream.
+*/
+private void writeClass(Class cl, boolean unshared) throws IOException {
+bout.writeByte(TC_CLASS);
+writeClassDesc(ObjectStreamClass.lookup(cl, true), false);
+handles.assign(unshared ? null : cl);
+}
+/**
+* Writes representation of given class descriptor to stream.
+*/
+private void writeClassDesc(ObjectStreamClass desc, boolean unshared)
+throws IOException
+{
+int handle;
+if (desc == null) {
+writeNull();
+} else if (!unshared && (handle = handles.lookup(desc)) != -1) {
+writeHandle(handle);
+} else if (desc.isProxy()) {
+writeProxyDesc(desc, unshared);
+} else {
+writeNonProxyDesc(desc, unshared);
+}
+}
+/**
+* Writes class descriptor representing a dynamic proxy class to stream.
+*/
+private void writeProxyDesc(ObjectStreamClass desc, boolean unshared)
+throws IOException
+{
+bout.writeByte(TC_PROXYCLASSDESC);
+handles.assign(unshared ? null : desc);
+Class cl = desc.forClass();
+Class[] ifaces = cl.getInterfaces();
+bout.writeInt(ifaces.length);
+for (int i = 0; i < ifaces.length; i++) {
+bout.writeUTF(ifaces[i].getName());
+}
+bout.setBlockDataMode(true);
+annotateProxyClass(cl);
+bout.setBlockDataMode(false);
+bout.writeByte(TC_ENDBLOCKDATA);
+writeClassDesc(desc.getSuperDesc(), false);
+}
+/**
+* Writes class descriptor representing a standard (i.e., not a dynamic
+* proxy) class to stream.
+*/
+private void writeNonProxyDesc(ObjectStreamClass desc, boolean unshared)
+throws IOException
+{
+bout.writeByte(TC_CLASSDESC);
+handles.assign(unshared ? null : desc);
+if (protocol == PROTOCOL_VERSION_1) {
+// do not invoke class descriptor write hook with old protocol
+desc.writeNonProxy(this);
+} else {
+writeClassDescriptor(desc);
+}
+Class cl = desc.forClass();
+bout.setBlockDataMode(true);
+annotateClass(cl);
+bout.setBlockDataMode(false);
+bout.writeByte(TC_ENDBLOCKDATA);
+writeClassDesc(desc.getSuperDesc(), false);
+}
+/**
+* Writes given string to stream, using standard or long UTF format
+* depending on string length.
+*/
+private void writeString(String str, boolean unshared) throws IOException {
+handles.assign(unshared ? null : str);
+long utflen = bout.getUTFLength(str);
+if (utflen <= 0xFFFF) {
+bout.writeByte(TC_STRING);
+bout.writeUTF(str, utflen);
+} else {
+bout.writeByte(TC_LONGSTRING);
+bout.writeLongUTF(str, utflen);
+}
+}
+/**
+* Writes given array object to stream.
+*/
+private void writeArray(Object array,
+ObjectStreamClass desc,
+boolean unshared)
+throws IOException
+{
+bout.writeByte(TC_ARRAY);
+writeClassDesc(desc, false);
+handles.assign(unshared ? null : array);
+Class ccl = desc.forClass().getComponentType();
+if (ccl.isPrimitive()) {
+if (ccl == Integer.TYPE) {
+int[] ia = (int[]) array;
+bout.writeInt(ia.length);
+bout.writeInts(ia, 0, ia.length);
+} else if (ccl == Byte.TYPE) {
+byte[] ba = (byte[]) array;
+bout.writeInt(ba.length);
+bout.write(ba, 0, ba.length, true);
+} else if (ccl == Long.TYPE) {
+long[] ja = (long[]) array;
+bout.writeInt(ja.length);
+bout.writeLongs(ja, 0, ja.length);
+} else if (ccl == Float.TYPE) {
+float[] fa = (float[]) array;
+bout.writeInt(fa.length);
+bout.writeFloats(fa, 0, fa.length);
+} else if (ccl == Double.TYPE) {
+double[] da = (double[]) array;
+bout.writeInt(da.length);
+bout.writeDoubles(da, 0, da.length);
+} else if (ccl == Short.TYPE) {
+short[] sa = (short[]) array;
+bout.writeInt(sa.length);
+bout.writeShorts(sa, 0, sa.length);
+} else if (ccl == Character.TYPE) {
+char[] ca = (char[]) array;
+bout.writeInt(ca.length);
+bout.writeChars(ca, 0, ca.length);
+} else if (ccl == Boolean.TYPE) {
+boolean[] za = (boolean[]) array;
+bout.writeInt(za.length);
+bout.writeBooleans(za, 0, za.length);
+} else {
+throw new InternalError();
+}
+} else {
+Object[] objs = (Object[]) array;
+int len = objs.length;
+bout.writeInt(len);
+if (extendedDebugInfo) {
+debugInfoStack.push(
+"array (class \"" + array.getClass().getName() +
+"\", size: " + len  + ")");
+}
+try {
+for (int i = 0; i < len; i++) {
+if (extendedDebugInfo) {
+debugInfoStack.push(
+"element of array (index: " + i + ")");
+}
+try {
+writeObject0(objs[i], false);
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+}
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+}
+}
+/**
+* Writes given enum constant to stream.
+*/
+private void writeEnum(Enum en,
+ObjectStreamClass desc,
+boolean unshared)
+throws IOException
+{
+bout.writeByte(TC_ENUM);
+ObjectStreamClass sdesc = desc.getSuperDesc();
+writeClassDesc((sdesc.forClass() == Enum.class) ? desc : sdesc, false);
+handles.assign(unshared ? null : en);
+writeString(en.name(), false);
+}
+/**
+* Writes representation of a "ordinary" (i.e., not a String, Class,
+* ObjectStreamClass, array, or enum constant) serializable object to the
+* stream.
+*/
+private void writeOrdinaryObject(Object obj,
+ObjectStreamClass desc,
+boolean unshared)
+throws IOException
+{
+if (extendedDebugInfo) {
+debugInfoStack.push(
+(depth == 1 ? "root " : "") + "object (class \"" +
+obj.getClass().getName() + "\", " + obj.toString() + ")");
+}
+try {
+desc.checkSerialize();
+bout.writeByte(TC_OBJECT);
+writeClassDesc(desc, false);
+handles.assign(unshared ? null : obj);
+if (desc.isExternalizable() && !desc.isProxy()) {
+writeExternalData((Externalizable) obj);
+} else {
+writeSerialData(obj, desc);
+}
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+}
+/**
+* Writes externalizable data of given object by invoking its
+* writeExternal() method.
+*/
+private void writeExternalData(Externalizable obj) throws IOException {
+Object oldObj = curObj;
+ObjectStreamClass oldDesc = curDesc;
+PutFieldImpl oldPut = curPut;
+curObj = obj;
+curDesc = null;
+curPut = null;
+if (extendedDebugInfo) {
+debugInfoStack.push("writeExternal data");
+}
+try {
+if (protocol == PROTOCOL_VERSION_1) {
+obj.writeExternal(this);
+} else {
+bout.setBlockDataMode(true);
+obj.writeExternal(this);
+bout.setBlockDataMode(false);
+bout.writeByte(TC_ENDBLOCKDATA);
+}
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+curObj = oldObj;
+curDesc = oldDesc;
+curPut = oldPut;
+}
+/**
+* Writes instance data for each serializable class of given object, from
+* superclass to subclass.
+*/
+private void writeSerialData(Object obj, ObjectStreamClass desc)
+throws IOException
+{
+ObjectStreamClass.ClassDataSlot[] slots = desc.getClassDataLayout();
+for (int i = 0; i < slots.length; i++) {
+ObjectStreamClass slotDesc = slots[i].desc;
+if (slotDesc.hasWriteObjectMethod()) {
+Object oldObj = curObj;
+ObjectStreamClass oldDesc = curDesc;
+PutFieldImpl oldPut = curPut;
+curObj = obj;
+curDesc = slotDesc;
+curPut = null;
+if (extendedDebugInfo) {
+debugInfoStack.push(
+"custom writeObject data (class \"" +
+slotDesc.getName() + "\")");
+}
+try {
+bout.setBlockDataMode(true);
+slotDesc.invokeWriteObject(obj, this);
+bout.setBlockDataMode(false);
+bout.writeByte(TC_ENDBLOCKDATA);
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+curObj = oldObj;
+curDesc = oldDesc;
+curPut = oldPut;
+} else {
+defaultWriteFields(obj, slotDesc);
+}
+}
+}
+/**
+* Fetches and writes values of serializable fields of given object to
+* stream.  The given class descriptor specifies which field values to
+* write, and in which order they should be written.
+*/
+private void defaultWriteFields(Object obj, ObjectStreamClass desc)
+throws IOException
+{
+// REMIND: perform conservative isInstance check here?
+desc.checkDefaultSerialize();
+int primDataSize = desc.getPrimDataSize();
+if (primVals == null || primVals.length < primDataSize) {
+primVals = new byte[primDataSize];
+}
+desc.getPrimFieldValues(obj, primVals);
+bout.write(primVals, 0, primDataSize, false);
+ObjectStreamField[] fields = desc.getFields(false);
+Object[] objVals = new Object[desc.getNumObjFields()];
+int numPrimFields = fields.length - objVals.length;
+desc.getObjFieldValues(obj, objVals);
+for (int i = 0; i < objVals.length; i++) {
+if (extendedDebugInfo) {
+debugInfoStack.push(
+"field (class \"" + desc.getName() + "\", name: \"" +
+fields[numPrimFields + i].getName() + "\", type: \"" +
+fields[numPrimFields + i].getType() + "\")");
+}
+try {
+writeObject0(objVals[i],
+fields[numPrimFields + i].isUnshared());
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+}
+}
+/**
+* Attempts to write to stream fatal IOException that has caused
+* serialization to abort.
+*/
+private void writeFatalException(IOException ex) throws IOException {
+/*
+* Note: the serialization specification states that if a second
+* IOException occurs while attempting to serialize the original fatal
+* exception to the stream, then a StreamCorruptedException should be
+* thrown (section 2.1).  However, due to a bug in previous
+* implementations of serialization, StreamCorruptedExceptions were
+* rarely (if ever) actually thrown--the "root" exceptions from
+* underlying streams were thrown instead.  This historical behavior is
+* followed here for consistency.
+*/
+clear();
+boolean oldMode = bout.setBlockDataMode(false);
+try {
+bout.writeByte(TC_EXCEPTION);
+writeObject0(ex, false);
+clear();
+} finally {
+bout.setBlockDataMode(oldMode);
+}
+}
+/**
+* Converts specified span of float values into byte values.
+*/
+// REMIND: remove once hotspot inlines Float.floatToIntBits
+private static native void floatsToBytes(float[] src, int srcpos,
+byte[] dst, int dstpos,
+int nfloats);
+/**
+* Converts specified span of double values into byte values.
+*/
+// REMIND: remove once hotspot inlines Double.doubleToLongBits
+private static native void doublesToBytes(double[] src, int srcpos,
+byte[] dst, int dstpos,
+int ndoubles);
+/**
+* Default PutField implementation.
+*/
+private class PutFieldImpl extends PutField {
+/** class descriptor describing serializable fields */
+private final ObjectStreamClass desc;
+/** primitive field values */
+private final byte[] primVals;
+/** object field values */
+private final Object[] objVals;
+/**
+* Creates PutFieldImpl object for writing fields defined in given
+* class descriptor.
+*/
+PutFieldImpl(ObjectStreamClass desc) {
+this.desc = desc;
+primVals = new byte[desc.getPrimDataSize()];
+objVals = new Object[desc.getNumObjFields()];
+}
+public void put(String name, boolean val) {
+Bits.putBoolean(primVals, getFieldOffset(name, Boolean.TYPE), val);
+}
+public void put(String name, byte val) {
+primVals[getFieldOffset(name, Byte.TYPE)] = val;
+}
+public void put(String name, char val) {
+Bits.putChar(primVals, getFieldOffset(name, Character.TYPE), val);
+}
+public void put(String name, short val) {
+Bits.putShort(primVals, getFieldOffset(name, Short.TYPE), val);
+}
+public void put(String name, int val) {
+Bits.putInt(primVals, getFieldOffset(name, Integer.TYPE), val);
+}
+public void put(String name, float val) {
+Bits.putFloat(primVals, getFieldOffset(name, Float.TYPE), val);
+}
+public void put(String name, long val) {
+Bits.putLong(primVals, getFieldOffset(name, Long.TYPE), val);
+}
+public void put(String name, double val) {
+Bits.putDouble(primVals, getFieldOffset(name, Double.TYPE), val);
+}
+public void put(String name, Object val) {
+objVals[getFieldOffset(name, Object.class)] = val;
+}
+// deprecated in ObjectOutputStream.PutField
+public void write(ObjectOutput out) throws IOException {
+/*
+* Applications should *not* use this method to write PutField
+* data, as it will lead to stream corruption if the PutField
+* object writes any primitive data (since block data mode is not
+* unset/set properly, as is done in OOS.writeFields()).  This
+* broken implementation is being retained solely for behavioral
+* compatibility, in order to support applications which use
+* OOS.PutField.write() for writing only non-primitive data.
+*
+* Serialization of unshared objects is not implemented here since
+* it is not necessary for backwards compatibility; also, unshared
+* semantics may not be supported by the given ObjectOutput
+* instance.  Applications which write unshared objects using the
+* PutField API must use OOS.writeFields().
+*/
+if (ObjectOutputStream.this != out) {
+throw new IllegalArgumentException("wrong stream");
+}
+out.write(primVals, 0, primVals.length);
+ObjectStreamField[] fields = desc.getFields(false);
+int numPrimFields = fields.length - objVals.length;
+// REMIND: warn if numPrimFields > 0?
+for (int i = 0; i < objVals.length; i++) {
+if (fields[numPrimFields + i].isUnshared()) {
+throw new IOException("cannot write unshared object");
+}
+out.writeObject(objVals[i]);
+}
+}
+/**
+* Writes buffered primitive data and object fields to stream.
+*/
+void writeFields() throws IOException {
+bout.write(primVals, 0, primVals.length, false);
+ObjectStreamField[] fields = desc.getFields(false);
+int numPrimFields = fields.length - objVals.length;
+for (int i = 0; i < objVals.length; i++) {
+if (extendedDebugInfo) {
+debugInfoStack.push(
+"field (class \"" + desc.getName() + "\", name: \"" +
+fields[numPrimFields + i].getName() + "\", type: \"" +
+fields[numPrimFields + i].getType() + "\")");
+}
+try {
+writeObject0(objVals[i],
+fields[numPrimFields + i].isUnshared());
+} finally {
+if (extendedDebugInfo) {
+debugInfoStack.pop();
+}
+}
+}
+}
+/**
+* Returns offset of field with given 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.
+* Throws IllegalArgumentException if no matching field found.
+*/
+private int getFieldOffset(String name, Class type) {
+ObjectStreamField field = desc.getField(name, type);
+if (field == null) {
+throw new IllegalArgumentException("no such field " + name +
+" with type " + type);
+}
+return field.getOffset();
+}
+}
+/**
+* Buffered output stream with two modes: in default mode, outputs data in
+* same format as DataOutputStream; in "block data" mode, outputs data
+* bracketed by block data markers (see object serialization specification
+* for details).
+*/
+private static class BlockDataOutputStream
+extends OutputStream implements DataOutput
+{
+/** maximum data block length */
+private static final int MAX_BLOCK_SIZE = 1024;
+/** maximum data block header length */
+private static final int MAX_HEADER_SIZE = 5;
+/** (tunable) length of char buffer (for writing strings) */
+private static final int CHAR_BUF_SIZE = 256;
+/** buffer for writing general/block data */
+private final byte[] buf = new byte[MAX_BLOCK_SIZE];
+/** buffer for writing block data headers */
+private final byte[] hbuf = new byte[MAX_HEADER_SIZE];
+/** char buffer for fast string writes */
+private final char[] cbuf = new char[CHAR_BUF_SIZE];
+/** block data mode */
+private boolean blkmode = false;
+/** current offset into buf */
+private int pos = 0;
+/** underlying output stream */
+private final OutputStream out;
+/** loopback stream (for data writes that span data blocks) */
+private final DataOutputStream dout;
+/**
+* Creates new BlockDataOutputStream on top of given underlying stream.
+* Block data mode is turned off by default.
+*/
+BlockDataOutputStream(OutputStream out) {
+this.out = out;
+dout = new DataOutputStream(this);
+}
+/**
+* Sets block data mode to the given mode (true == on, false == off)
+* and returns the previous mode value.  If the new mode is the same as
+* the old mode, no action is taken.  If the new mode differs from the
+* old mode, any buffered data is flushed before switching to the new
+* mode.
+*/
+boolean setBlockDataMode(boolean mode) throws IOException {
+if (blkmode == mode) {
+return blkmode;
+}
+drain();
+blkmode = mode;
+return !blkmode;
+}
+/**
+* Returns true if the stream is currently in block data mode, false
+* otherwise.
+*/
+boolean getBlockDataMode() {
+return blkmode;
+}
+/* ----------------- generic output stream methods ----------------- */
+/*
+* The following methods are equivalent to their counterparts in
+* OutputStream, except that they partition written data into data
+* blocks when in block data mode.
+*/
+public void write(int b) throws IOException {
+if (pos >= MAX_BLOCK_SIZE) {
+drain();
+}
+buf[pos++] = (byte) b;
+}
+public void write(byte[] b) throws IOException {
+write(b, 0, b.length, false);
+}
+public void write(byte[] b, int off, int len) throws IOException {
+write(b, off, len, false);
+}
+public void flush() throws IOException {
+drain();
+out.flush();
+}
+public void close() throws IOException {
+flush();
+out.close();
+}
+/**
+* Writes specified span of byte values from given array.  If copy is
+* true, copies the values to an intermediate buffer before writing
+* them to underlying stream (to avoid exposing a reference to the
+* original byte array).
+*/
+void write(byte[] b, int off, int len, boolean copy)
+throws IOException
+{
+if (!(copy || blkmode)) {           // write directly
+drain();
+out.write(b, off, len);
+return;
+}
+while (len > 0) {
+if (pos >= MAX_BLOCK_SIZE) {
+drain();
+}
+if (len >= MAX_BLOCK_SIZE && !copy && pos == 0) {
+// avoid unnecessary copy
+writeBlockHeader(MAX_BLOCK_SIZE);
+out.write(b, off, MAX_BLOCK_SIZE);
+off += MAX_BLOCK_SIZE;
+len -= MAX_BLOCK_SIZE;
+} else {
+int wlen = Math.min(len, MAX_BLOCK_SIZE - pos);
+System.arraycopy(b, off, buf, pos, wlen);
+pos += wlen;
+off += wlen;
+len -= wlen;
+}
+}
+}
+/**
+* Writes all buffered data from this stream to the underlying stream,
+* but does not flush underlying stream.
+*/
+void drain() throws IOException {
+if (pos == 0) {
+return;
+}
+if (blkmode) {
+writeBlockHeader(pos);
+}
+out.write(buf, 0, pos);
+pos = 0;
+}
+/**
+* Writes block data header.  Data blocks shorter than 256 bytes are
+* prefixed with a 2-byte header; all others start with a 5-byte
+* header.
+*/
+private void writeBlockHeader(int len) throws IOException {
+if (len <= 0xFF) {
+hbuf[0] = TC_BLOCKDATA;
+hbuf[1] = (byte) len;
+out.write(hbuf, 0, 2);
+} else {
+hbuf[0] = TC_BLOCKDATALONG;
+Bits.putInt(hbuf, 1, len);
+out.write(hbuf, 0, 5);
+}
+}
+/* ----------------- primitive data output methods ----------------- */
+/*
+* The following methods are equivalent to their counterparts in
+* DataOutputStream, except that they partition written data into data
+* blocks when in block data mode.
+*/
+public void writeBoolean(boolean v) throws IOException {
+if (pos >= MAX_BLOCK_SIZE) {
+drain();
+}
+Bits.putBoolean(buf, pos++, v);
+}
+public void writeByte(int v) throws IOException {
+if (pos >= MAX_BLOCK_SIZE) {
+drain();
+}
+buf[pos++] = (byte) v;
+}
+public void writeChar(int v) throws IOException {
+if (pos + 2 <= MAX_BLOCK_SIZE) {
+Bits.putChar(buf, pos, (char) v);
+pos += 2;
+} else {
+dout.writeChar(v);
+}
+}
+public void writeShort(int v) throws IOException {
+if (pos + 2 <= MAX_BLOCK_SIZE) {
+Bits.putShort(buf, pos, (short) v);
+pos += 2;
+} else {
+dout.writeShort(v);
+}
+}
+public void writeInt(int v) throws IOException {
+if (pos + 4 <= MAX_BLOCK_SIZE) {
+Bits.putInt(buf, pos, v);
+pos += 4;
+} else {
+dout.writeInt(v);
+}
+}
+public void writeFloat(float v) throws IOException {
+if (pos + 4 <= MAX_BLOCK_SIZE) {
+Bits.putFloat(buf, pos, v);
+pos += 4;
+} else {
+dout.writeFloat(v);
+}
+}
+public void writeLong(long v) throws IOException {
+if (pos + 8 <= MAX_BLOCK_SIZE) {
+Bits.putLong(buf, pos, v);
+pos += 8;
+} else {
+dout.writeLong(v);
+}
+}
+public void writeDouble(double v) throws IOException {
+if (pos + 8 <= MAX_BLOCK_SIZE) {
+Bits.putDouble(buf, pos, v);
+pos += 8;
+} else {
+dout.writeDouble(v);
+}
+}
+public void writeBytes(String s) throws IOException {
+int endoff = s.length();
+int cpos = 0;
+int csize = 0;
+for (int off = 0; off < endoff; ) {
+if (cpos >= csize) {
+cpos = 0;
+csize = Math.min(endoff - off, CHAR_BUF_SIZE);
+s.getChars(off, off + csize, cbuf, 0);
+}
+if (pos >= MAX_BLOCK_SIZE) {
+drain();
+}
+int n = Math.min(csize - cpos, MAX_BLOCK_SIZE - pos);
+int stop = pos + n;
+while (pos < stop) {
+buf[pos++] = (byte) cbuf[cpos++];
+}
+off += n;
+}
+}
+public void writeChars(String s) throws IOException {
+int endoff = s.length();
+for (int off = 0; off < endoff; ) {
+int csize = Math.min(endoff - off, CHAR_BUF_SIZE);
+s.getChars(off, off + csize, cbuf, 0);
+writeChars(cbuf, 0, csize);
+off += csize;
+}
+}
+public void writeUTF(String s) throws IOException {
+writeUTF(s, getUTFLength(s));
+}
+/* -------------- primitive data array output methods -------------- */
+/*
+* The following methods write out spans of primitive data values.
+* Though equivalent to calling the corresponding primitive write
+* methods repeatedly, these methods are optimized for writing groups
+* of primitive data values more efficiently.
+*/
+void writeBooleans(boolean[] v, int off, int len) throws IOException {
+int endoff = off + len;
+while (off < endoff) {
+if (pos >= MAX_BLOCK_SIZE) {
+drain();
+}
+int stop = Math.min(endoff, off + (MAX_BLOCK_SIZE - pos));
+while (off < stop) {
+Bits.putBoolean(buf, pos++, v[off++]);
+}
+}
+}
+void writeChars(char[] v, int off, int len) throws IOException {
+int limit = MAX_BLOCK_SIZE - 2;
+int endoff = off + len;
+while (off < endoff) {
+if (pos <= limit) {
+int avail = (MAX_BLOCK_SIZE - pos) >> 1;
+int stop = Math.min(endoff, off + avail);
+while (off < stop) {
+Bits.putChar(buf, pos, v[off++]);
+pos += 2;
+}
+} else {
+dout.writeChar(v[off++]);
+}
+}
+}
+void writeShorts(short[] v, int off, int len) throws IOException {
+int limit = MAX_BLOCK_SIZE - 2;
+int endoff = off + len;
+while (off < endoff) {
+if (pos <= limit) {
+int avail = (MAX_BLOCK_SIZE - pos) >> 1;
+int stop = Math.min(endoff, off + avail);
+while (off < stop) {
+Bits.putShort(buf, pos, v[off++]);
+pos += 2;
+}
+} else {
+dout.writeShort(v[off++]);
+}
+}
+}
+void writeInts(int[] v, int off, int len) throws IOException {
+int limit = MAX_BLOCK_SIZE - 4;
+int endoff = off + len;
+while (off < endoff) {
+if (pos <= limit) {
+int avail = (MAX_BLOCK_SIZE - pos) >> 2;
+int stop = Math.min(endoff, off + avail);
+while (off < stop) {
+Bits.putInt(buf, pos, v[off++]);
+pos += 4;
+}
+} else {
+dout.writeInt(v[off++]);
+}
+}
+}
+void writeFloats(float[] v, int off, int len) throws IOException {
+int limit = MAX_BLOCK_SIZE - 4;
+int endoff = off + len;
+while (off < endoff) {
+if (pos <= limit) {
+int avail = (MAX_BLOCK_SIZE - pos) >> 2;
+int chunklen = Math.min(endoff - off, avail);
+floatsToBytes(v, off, buf, pos, chunklen);
+off += chunklen;
+pos += chunklen << 2;
+} else {
+dout.writeFloat(v[off++]);
+}
+}
+}
+void writeLongs(long[] v, int off, int len) throws IOException {
+int limit = MAX_BLOCK_SIZE - 8;
+int endoff = off + len;
+while (off < endoff) {
+if (pos <= limit) {
+int avail = (MAX_BLOCK_SIZE - pos) >> 3;
+int stop = Math.min(endoff, off + avail);
+while (off < stop) {
+Bits.putLong(buf, pos, v[off++]);
+pos += 8;
+}
+} else {
+dout.writeLong(v[off++]);
+}
+}
+}
+void writeDoubles(double[] v, int off, int len) throws IOException {
+int limit = MAX_BLOCK_SIZE - 8;
+int endoff = off + len;
+while (off < endoff) {
+if (pos <= limit) {
+int avail = (MAX_BLOCK_SIZE - pos) >> 3;
+int chunklen = Math.min(endoff - off, avail);
+doublesToBytes(v, off, buf, pos, chunklen);
+off += chunklen;
+pos += chunklen << 3;
+} else {
+dout.writeDouble(v[off++]);
+}
+}
+}
+/**
+* Returns the length in bytes of the UTF encoding of the given string.
+*/
+long getUTFLength(String s) {
+int len = s.length();
+long utflen = 0;
+for (int off = 0; off < len; ) {
+int csize = Math.min(len - off, CHAR_BUF_SIZE);
+s.getChars(off, off + csize, cbuf, 0);
+for (int cpos = 0; cpos < csize; cpos++) {
+char c = cbuf[cpos];
+if (c >= 0x0001 && c <= 0x007F) {
+utflen++;
+} else if (c > 0x07FF) {
+utflen += 3;
+} else {
+utflen += 2;
+}
+}
+off += csize;
+}
+return utflen;
+}
+/**
+* Writes the given string in UTF format.  This method is used in
+* situations where the UTF encoding length of the string is already
+* known; specifying it explicitly avoids a prescan of the string to
+* determine its UTF length.
+*/
+void writeUTF(String s, long utflen) throws IOException {
+if (utflen > 0xFFFFL) {
+throw new UTFDataFormatException();
+}
+writeShort((int) utflen);
+if (utflen == (long) s.length()) {
+writeBytes(s);
+} else {
+writeUTFBody(s);
+}
+}
+/**
+* Writes given string in "long" UTF format.  "Long" UTF format is
+* identical to standard UTF, except that it uses an 8 byte header
+* (instead of the standard 2 bytes) to convey the UTF encoding length.
+*/
+void writeLongUTF(String s) throws IOException {
+writeLongUTF(s, getUTFLength(s));
+}
+/**
+* Writes given string in "long" UTF format, where the UTF encoding
+* length of the string is already known.
+*/
+void writeLongUTF(String s, long utflen) throws IOException {
+writeLong(utflen);
+if (utflen == (long) s.length()) {
+writeBytes(s);
+} else {
+writeUTFBody(s);
+}
+}
+/**
+* Writes the "body" (i.e., the UTF representation minus the 2-byte or
+* 8-byte length header) of the UTF encoding for the given string.
+*/
+private void writeUTFBody(String s) throws IOException {
+int limit = MAX_BLOCK_SIZE - 3;
+int len = s.length();
+for (int off = 0; off < len; ) {
+int csize = Math.min(len - off, CHAR_BUF_SIZE);
+s.getChars(off, off + csize, cbuf, 0);
+for (int cpos = 0; cpos < csize; cpos++) {
+char c = cbuf[cpos];
+if (pos <= limit) {
+if (c <= 0x007F && c != 0) {
+buf[pos++] = (byte) c;
+} else if (c > 0x07FF) {
+buf[pos + 2] = (byte) (0x80 | ((c >> 0) & 0x3F));
+buf[pos + 1] = (byte) (0x80 | ((c >> 6) & 0x3F));
+buf[pos + 0] = (byte) (0xE0 | ((c >> 12) & 0x0F));
+pos += 3;
+} else {
+buf[pos + 1] = (byte) (0x80 | ((c >> 0) & 0x3F));
+buf[pos + 0] = (byte) (0xC0 | ((c >> 6) & 0x1F));
+pos += 2;
+}
+} else {    // write one byte at a time to normalize block
+if (c <= 0x007F && c != 0) {
+write(c);
+} else if (c > 0x07FF) {
+write(0xE0 | ((c >> 12) & 0x0F));
+write(0x80 | ((c >> 6) & 0x3F));
+write(0x80 | ((c >> 0) & 0x3F));
+} else {
+write(0xC0 | ((c >> 6) & 0x1F));
+write(0x80 | ((c >> 0) & 0x3F));
+}
+}
+}
+off += csize;
+}
+}
+}
+/**
+* Lightweight identity hash table which maps objects to integer handles,
+* assigned in ascending order.
+*/
+private static class HandleTable {
+/* number of mappings in table/next available handle */
+private int size;
+/* size threshold determining when to expand hash spine */
+private int threshold;
+/* factor for computing size threshold */
+private final float loadFactor;
+/* maps hash value -> candidate handle value */
+private int[] spine;
+/* maps handle value -> next candidate handle value */
+private int[] next;
+/* maps handle value -> associated object */
+private Object[] objs;
+/**
+* Creates new HandleTable with given capacity and load factor.
+*/
+HandleTable(int initialCapacity, float loadFactor) {
+this.loadFactor = loadFactor;
+spine = new int[initialCapacity];
+next = new int[initialCapacity];
+objs = new Object[initialCapacity];
+threshold = (int) (initialCapacity * loadFactor);
+clear();
+}
+/**
+* Assigns next available handle to given object, and returns handle
+* value.  Handles are assigned in ascending order starting at 0.
+*/
+int assign(Object obj) {
+if (size >= next.length) {
+growEntries();
+}
+if (size >= threshold) {
+growSpine();
+}
+insert(obj, size);
+return size++;
+}
+/**
+* Looks up and returns handle associated with given object, or -1 if
+* no mapping found.
+*/
+int lookup(Object obj) {
+if (size == 0) {
+return -1;
+}
+int index = hash(obj) % spine.length;
+for (int i = spine[index]; i >= 0; i = next[i]) {
+if (objs[i] == obj) {
+return i;
+}
+}
+return -1;
+}
+/**
+* Resets table to its initial (empty) state.
+*/
+void clear() {
+Arrays.fill(spine, -1);
+Arrays.fill(objs, 0, size, null);
+size = 0;
+}
+/**
+* Returns the number of mappings currently in table.
+*/
+int size() {
+return size;
+}
+/**
+* Inserts mapping object -> handle mapping into table.  Assumes table
+* is large enough to accommodate new mapping.
+*/
+private void insert(Object obj, int handle) {
+int index = hash(obj) % spine.length;
+objs[handle] = obj;
+next[handle] = spine[index];
+spine[index] = handle;
+}
+/**
+* Expands the hash "spine" -- equivalent to increasing the number of
+* buckets in a conventional hash table.
+*/
+private void growSpine() {
+spine = new int[(spine.length << 1) + 1];
+threshold = (int) (spine.length * loadFactor);
+Arrays.fill(spine, -1);
+for (int i = 0; i < size; i++) {
+insert(objs[i], i);
+}
+}
+/**
+* Increases hash table capacity by lengthening entry arrays.
+*/
+private void growEntries() {
+int newLength = (next.length << 1) + 1;
+int[] newNext = new int[newLength];
+System.arraycopy(next, 0, newNext, 0, size);
+next = newNext;
+Object[] newObjs = new Object[newLength];
+System.arraycopy(objs, 0, newObjs, 0, size);
+objs = newObjs;
+}
+/**
+* Returns hash value for given object.
+*/
+private int hash(Object obj) {
+return System.identityHashCode(obj) & 0x7FFFFFFF;
+}
+}
+/**
+* Lightweight identity hash table which maps objects to replacement
+* objects.
+*/
+private static class ReplaceTable {
+/* maps object -> index */
+private final HandleTable htab;
+/* maps index -> replacement object */
+private Object[] reps;
+/**
+* Creates new ReplaceTable with given capacity and load factor.
+*/
+ReplaceTable(int initialCapacity, float loadFactor) {
+htab = new HandleTable(initialCapacity, loadFactor);
+reps = new Object[initialCapacity];
+}
+/**
+* Enters mapping from object to replacement object.
+*/
+void assign(Object obj, Object rep) {
+int index = htab.assign(obj);
+while (index >= reps.length) {
+grow();
+}
+reps[index] = rep;
+}
+/**
+* Looks up and returns replacement for given object.  If no
+* replacement is found, returns the lookup object itself.
+*/
+Object lookup(Object obj) {
+int index = htab.lookup(obj);
+return (index >= 0) ? reps[index] : obj;
+}
+/**
+* Resets table to its initial (empty) state.
+*/
+void clear() {
+Arrays.fill(reps, 0, htab.size(), null);
+htab.clear();
+}
+/**
+* Returns the number of mappings currently in table.
+*/
+int size() {
+return htab.size();
+}
+/**
+* Increases table capacity.
+*/
+private void grow() {
+Object[] newReps = new Object[(reps.length << 1) + 1];
+System.arraycopy(reps, 0, newReps, 0, reps.length);
+reps = newReps;
+}
+}
+/**
+* Stack to keep debug information about the state of the
+* serialization process, for embedding in exception messages.
+*/
+private static class DebugTraceInfoStack {
+private final List<String> stack;
+DebugTraceInfoStack() {
+stack = new ArrayList<String>();
+}
+/**
+* Removes all of the elements from enclosed list.
+*/
+void clear() {
+stack.clear();
+}
+/**
+* Removes the object at the top of enclosed list.
+*/
+void pop() {
+stack.remove(stack.size()-1);
+}
+/**
+* Pushes a String onto the top of enclosed list.
+*/
+void push(String entry) {
+stack.add("\t- " + entry);
+}
+/**
+* Returns a string representation of this object
+*/
+public String toString() {
+StringBuilder buffer = new StringBuilder();
+if (!stack.isEmpty()) {
+for(int i = stack.size(); i > 0; i-- ) {
+buffer.append(stack.get(i-1) + ((i != 1) ? "\n" : ""));
+}
+}
+return buffer.toString();
+}
+}
+}

changeset 2	90ce3da70b43
child 5506	202f599c92aa