gt:         Class<?> cl = desc.forClass();
context: /*
   * Copyright (c) 1996, 2014, 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.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.StringJoiner;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import static java.io.ObjectStreamClass.processQueue;
  import sun.reflect.misc.ReflectUtil;
  
  /**
   * 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       1.1
   */
  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<>();
  
          /** queue for WeakReferences to audited subclasses */
          static final ReferenceQueue<Class<?>> subclassAuditsQueue =
              new ReferenceQueue<>();
      }
  
      /** 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()
      /**
       * Context during upcalls to class-defined writeObject methods; holds
       * object currently being serialized and descriptor for current class.
       * Null when not during writeObject upcall.
       */
      private SerialCallbackContext curContext;
      /** 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.
       * @throws  IOException if an I/O error occurs while creating this stream
       * @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 {
          SerialCallbackContext ctx = curContext;
          if (ctx == null) {
              throw new NotActiveException("not in call to writeObject");
          }
          Object curObj = ctx.getObj();
          ObjectStreamClass curDesc = ctx.getDesc();
          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) {
              SerialCallbackContext ctx = curContext;
              if (ctx == null) {
                  throw new NotActiveException("not in call to writeObject");
              }
              ctx.checkAndSetUsed();
              ObjectStreamClass curDesc = ctx.getDesc();
              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 referred 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 abstract static 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 = auditSubclass(cl);
              Caches.subclassAudits.putIfAbsent(key, result);
          }
          if (!result) {
              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(Class<?> subcl) {
          return AccessController.doPrivileged(
              new PrivilegedAction<>() {
                  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;
                  }
              }
          );
      }
  
      /**
       * 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);
          }
      }
  
      private boolean isCustomSubclass() {
          // Return true if this class is a custom subclass of ObjectOutputStream
          return getClass().getClassLoader()
                     != ObjectOutputStream.class.getClassLoader();
      }
  
      /**
       * 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);
          if (cl != null && isCustomSubclass()) {
              ReflectUtil.checkPackageAccess(cl);
          }
          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);
          if (cl != null && isCustomSubclass()) {
              ReflectUtil.checkPackageAccess(cl);
          }
          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 {
          PutFieldImpl oldPut = curPut;
          curPut = null;
  
          if (extendedDebugInfo) {
              debugInfoStack.push("writeExternal data");
          }
          SerialCallbackContext oldContext = curContext;
          try {
              curContext = null;
              if (protocol == PROTOCOL_VERSION_1) {
                  obj.writeExternal(this);
              } else {
                  bout.setBlockDataMode(true);
                  obj.writeExternal(this);
                  bout.setBlockDataMode(false);
                  bout.writeByte(TC_ENDBLOCKDATA);
              }
          } finally {
              curContext = oldContext;
              if (extendedDebugInfo) {
                  debugInfoStack.pop();
              }
          }
  
          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()) {
                  PutFieldImpl oldPut = curPut;
                  curPut = null;
                  SerialCallbackContext oldContext = curContext;
  
                  if (extendedDebugInfo) {
                      debugInfoStack.push(
                          "custom writeObject data (class \"" +
                          slotDesc.getName() + "\")");
                  }
                  try {
                      curContext = new SerialCallbackContext(obj, slotDesc);
                      bout.setBlockDataMode(true);
                      slotDesc.invokeWriteObject(obj, this);
                      bout.setBlockDataMode(false);
                      bout.writeByte(TC_ENDBLOCKDATA);
                  } finally {
                      curContext.setUsed();
                      curContext = oldContext;
                      if (extendedDebugInfo) {
                          debugInfoStack.pop();
                      }
                  }
  
                  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
      {
  