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java.io
Class ObjectOutputStream  

java.lang.Object
  java.io.OutputStream
      java.io.ObjectOutputStream

All Implemented Interfaces:

DataOutput, ObjectOutput, ObjectStreamConstants

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public class ObjectOutputStream

extends OutputStream

implements ObjectOutput, ObjectStreamConstants

An ObjectOutputStream can be used to write objects as well as primitive data in a platform-independent manner to an OutputStream. The data produced by an ObjectOutputStream can be read and reconstituted by an ObjectInputStream. writeObject (Object) is used to write Objects, the write<type> methods are used to write primitive data (as in DataOutputStream). Strings can be written as objects or as primitive data. Not all objects can be written out using an ObjectOutputStream. Only those objects that are an instance of java.io.Serializable can be written. Using default serialization, information about the class of an object is written, all of the non-transient, non-static fields of the object are written, if any of these fields are objects, they are written out in the same manner. An object is only written out the first time it is encountered. If the object is encountered later, a reference to it is written to the underlying stream. Thus writing circular object graphs does not present a problem, nor are relationships between objects in a graph lost. Example usage:

 Hashtable map = new Hashtable ();
 map.put ("one", new Integer (1));
 map.put ("two", new Integer (2));

 ObjectOutputStream oos =
 new ObjectOutputStream (new FileOutputStream ("numbers"));
 oos.writeObject (map);
 oos.close ();

 ObjectInputStream ois =
 new ObjectInputStream (new FileInputStream ("numbers"));
 Hashtable newmap = (Hashtable)ois.readObject ();

 System.out.println (newmap);
 

The default serialization can be overriden in two ways. By defining a method private void writeObject (ObjectOutputStream), a class can dictate exactly how information about itself is written. defaultWriteObject () may be called from this method to carry out default serialization. This method is not responsible for dealing with fields of super-classes or subclasses. By implementing java.io.Externalizable. This gives the class complete control over the way it is written to the stream. If this approach is used the burden of writing superclass and subclass data is transfered to the class implementing java.io.Externalizable.

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Nested Class Summary
static class	ObjectOutputStream.PutField           This class allows a class to specify exactly which fields should be written, and what values should be written for these fields.

 

Field Summary
private  byte[]	blockData
private  int	blockDataCount
private  DataOutputStream	blockDataOutput
private static int	BUFFER_SIZE
private  java.lang.Object	currentObject
(package private)  ObjectStreamClass	currentObjectStreamClass
private  ObjectOutputStream.PutField	currentPutField
private  DataOutputStream	dataOutput
private static boolean	DEBUG
private static int	defaultProtocolVersion
private  int	depth
private  boolean	dump
private  boolean	fieldsAlreadyWritten
private  boolean	isSerializing
private  int	nextOID
private  java.util.Hashtable	OIDLookupTable
private  int	protocolVersion
private  DataOutputStream	realOutput
private  boolean	replacementEnabled
private  gnu.java.security.action.SetAccessibleAction	setAccessible
private  boolean	useSubclassMethod
private  boolean	writeDataAsBlocks

 

Fields inherited from interface java.io.ObjectStreamConstants

baseWireHandle, PROTOCOL_VERSION_1, PROTOCOL_VERSION_2, SC_BLOCK_DATA, SC_EXTERNALIZABLE, SC_SERIALIZABLE, SC_WRITE_METHOD, STREAM_MAGIC, STREAM_VERSION, SUBCLASS_IMPLEMENTATION_PERMISSION, SUBSTITUTION_PERMISSION, TC_ARRAY, TC_BASE, TC_BLOCKDATA, TC_BLOCKDATALONG, TC_CLASS, TC_CLASSDESC, TC_ENDBLOCKDATA, TC_EXCEPTION, TC_LONGSTRING, TC_MAX, TC_NULL, TC_OBJECT, TC_PROXYCLASSDESC, TC_REFERENCE, TC_RESET, TC_STRING

 

Constructor Summary
protected	ObjectOutputStream()           Protected constructor that allows subclasses to override serialization.
	ObjectOutputStream(OutputStream out)           Creates a new ObjectOutputStream that will do all of its writing onto out.

 

Method Summary
protected  void	annotateClass(java.lang.Class cl)           An empty hook that allows subclasses to write extra information about classes to the stream.
protected  void	annotateProxyClass(java.lang.Class cl)
private  int	assignNewHandle(java.lang.Object obj)
private  void	callWriteMethod(java.lang.Object obj, ObjectStreamClass osc)
private  void	clearHandles()
void	close()           This method closes the underlying stream.
void	defaultWriteObject()           Writes the current objects non-transient, non-static fields from the current class to the underlying output stream.
protected  void	drain()           Causes the block-data buffer to be written to the underlying stream, but does not flush underlying stream.
private  void	dumpElementln(java.lang.String msg)
protected  boolean	enableReplaceObject(boolean enable)           If enable is true and this object is trusted, then replaceObject (Object) will be called in subsequent calls to writeObject (Object).
private  java.lang.Integer	findHandle(java.lang.Object obj)
void	flush()           This method causes any buffered data to be flushed out to the underlying stream
private  boolean	getBooleanField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  byte	getByteField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  char	getCharField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  double	getDoubleField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  java.lang.reflect.Field	getField(java.lang.Class klass, java.lang.String name)
private  float	getFloatField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  int	getIntField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  long	getLongField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  java.lang.Object	getObjectField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name, java.lang.String type_code)
private  short	getShortField(java.lang.Object obj, java.lang.Class klass, java.lang.String field_name)
private  void	markFieldsWritten()
ObjectOutputStream.PutField	putFields()
protected  java.lang.Object	replaceObject(java.lang.Object obj)           Allows subclasses to replace objects that are written to the stream with other objects to be written in their place.
void	reset()           Resets stream to state equivalent to the state just after it was constructed.
private  void	reset(boolean internal)
(package private)  boolean	setBlockDataMode(boolean on)
void	useProtocolVersion(int version)           Informs this ObjectOutputStream to write data according to the specified protocol.
void	write(byte[] b)           This method writes all the bytes in the specified byte array to the output stream.
void	write(byte[] b, int off, int len)           This method writes len bytes from the specified array starting at index offset into that array.
void	write(int data)           This method writes the specified byte to the output stream.
private  void	writeArraySizeAndElements(java.lang.Object array, java.lang.Class clazz)
private  void	writeBlockDataHeader(int size)
void	writeBoolean(boolean data)           This method writes a Java boolean value to an output stream.
void	writeByte(int data)           This method writes a Java byte value to an output stream.
void	writeBytes(java.lang.String data)           This method writes all the bytes in a String out to the stream.
void	writeChar(int data)           This method writes a Java char value to an output stream.
void	writeChars(java.lang.String data)           This method writes all the characters of a String to an output stream as an array of char's.
protected  void	writeClassDescriptor(ObjectStreamClass osc)
void	writeDouble(double data)           This method writes a Java double value to the stream.
void	writeFields()
private  void	writeFields(java.lang.Object obj, ObjectStreamClass osc)
void	writeFloat(float data)           This method writes a Java float value to the stream.
void	writeInt(int data)           This method writes a Java int value to an output stream.
void	writeLong(long data)           This method writes a Java long value to an output stream.
void	writeObject(java.lang.Object obj)           Writes a representation of obj to the underlying output stream by writing out information about its class, then writing out each of the objects non-transient, non-static fields.
protected  void	writeObjectOverride(java.lang.Object obj)           This method allows subclasses to override the default serialization mechanism provided by ObjectOutputStream.
void	writeShort(int data)           This method writes a Java short value to an output stream.
protected  void	writeStreamHeader()           Writes stream magic and stream version information to the underlying stream.
void	writeUTF(java.lang.String data)           This method writes a Java String to the stream in a modified UTF-8 format.

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Field Detail

BUFFER_SIZE

private static final int BUFFER_SIZE

See Also:

Constant Field Values

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defaultProtocolVersion

private static int defaultProtocolVersion

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dataOutput

private DataOutputStream dataOutput

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writeDataAsBlocks

private boolean writeDataAsBlocks

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realOutput

private DataOutputStream realOutput

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blockDataOutput

private DataOutputStream blockDataOutput

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blockData

private byte[] blockData

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blockDataCount

private int blockDataCount

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currentObject

private java.lang.Object currentObject

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currentObjectStreamClass

ObjectStreamClass currentObjectStreamClass

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currentPutField

private ObjectOutputStream.PutField currentPutField

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fieldsAlreadyWritten

private boolean fieldsAlreadyWritten

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replacementEnabled

private boolean replacementEnabled

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isSerializing

private boolean isSerializing

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nextOID

private int nextOID

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OIDLookupTable

private java.util.Hashtable OIDLookupTable

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protocolVersion

private int protocolVersion

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useSubclassMethod

private boolean useSubclassMethod

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setAccessible

private gnu.java.security.action.SetAccessibleAction setAccessible

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depth

private int depth

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dump

private boolean dump

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DEBUG

private static final boolean DEBUG

See Also:

Constant Field Values

Constructor Detail

ObjectOutputStream

public ObjectOutputStream(OutputStream out)
                   throws IOException

Creates a new ObjectOutputStream that will do all of its writing onto out. This method also initializes the stream by writing the header information (stream magic number and stream version).

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ObjectOutputStream

protected ObjectOutputStream()
                      throws IOException,
                             java.lang.SecurityException

Protected constructor that allows subclasses to override serialization. This constructor should be called by subclasses that wish to override writeObject (Object). This method does a security check NOTE: currently not implemented, then sets a flag that informs writeObject (Object) to call the subclasses writeObjectOverride (Object) method.

Method Detail

writeObject

public final void writeObject(java.lang.Object obj)
                       throws IOException

Writes a representation of obj to the underlying output stream by writing out information about its class, then writing out each of the objects non-transient, non-static fields. If any of these fields are other objects, they are written out in the same manner. This method can be overriden by a class by implementing private void writeObject (ObjectOutputStream). If an exception is thrown from this method, the stream is left in an undefined state.

Specified by:

writeObject in interface ObjectOutput

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writeClassDescriptor

protected void writeClassDescriptor(ObjectStreamClass osc)
                             throws IOException

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defaultWriteObject

public void defaultWriteObject()
                        throws IOException,
                               NotActiveException

Writes the current objects non-transient, non-static fields from the current class to the underlying output stream. This method is intended to be called from within a object's private void writeObject (ObjectOutputStream) method.

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markFieldsWritten

private void markFieldsWritten()
                        throws IOException

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reset

public void reset()
           throws IOException

Resets stream to state equivalent to the state just after it was constructed. Causes all objects previously written to the stream to be forgotten. A notification of this reset is also written to the underlying stream.

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reset

private void reset(boolean internal)
            throws IOException

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useProtocolVersion

public void useProtocolVersion(int version)
                        throws IOException

Informs this ObjectOutputStream to write data according to the specified protocol. There are currently two different protocols, specified by PROTOCOL_VERSION_1 and PROTOCOL_VERSION_2. This implementation writes data using PROTOCOL_VERSION_2 by default, as is done since the JDK 1.2.

For an explanation of the differences between the two protocols see the Java Object Serialization Specification.

Since:

1.2

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annotateClass

protected void annotateClass(java.lang.Class cl)
                      throws IOException

An empty hook that allows subclasses to write extra information about classes to the stream. This method is called the first time each class is seen, and after all of the standard information about the class has been written.

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annotateProxyClass

protected void annotateProxyClass(java.lang.Class cl)
                           throws IOException

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replaceObject

protected java.lang.Object replaceObject(java.lang.Object obj)
                                  throws IOException

Allows subclasses to replace objects that are written to the stream with other objects to be written in their place. This method is called the first time each object is encountered (modulo reseting of the stream). This method must be enabled before it will be called in the serialization process.

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enableReplaceObject

protected boolean enableReplaceObject(boolean enable)
                               throws java.lang.SecurityException

If enable is true and this object is trusted, then replaceObject (Object) will be called in subsequent calls to writeObject (Object). Otherwise, replaceObject (Object) will not be called.

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writeStreamHeader

protected void writeStreamHeader()
                          throws IOException

Writes stream magic and stream version information to the underlying stream.

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writeObjectOverride

protected void writeObjectOverride(java.lang.Object obj)
                            throws NotActiveException,
                                   IOException

This method allows subclasses to override the default serialization mechanism provided by ObjectOutputStream. To make this method be used for writing objects, subclasses must invoke the 0-argument constructor on this class from there constructor.

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write

public void write(int data)
           throws IOException

Description copied from interface: ObjectOutput

This method writes the specified byte to the output stream.

Specified by:

write in interface ObjectOutput

Specified by:

write in class OutputStream

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write

public void write(byte[] b)
           throws IOException

Description copied from interface: ObjectOutput

This method writes all the bytes in the specified byte array to the output stream.

Specified by:

write in interface ObjectOutput

Overrides:

write in class OutputStream

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write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException

Description copied from interface: ObjectOutput

This method writes len bytes from the specified array starting at index offset into that array.

Specified by:

write in interface ObjectOutput

Overrides:

write in class OutputStream

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flush

public void flush()
           throws IOException

Description copied from interface: ObjectOutput

This method causes any buffered data to be flushed out to the underlying stream

Specified by:

flush in interface ObjectOutput

Overrides:

flush in class OutputStream

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drain

protected void drain()
              throws IOException

Causes the block-data buffer to be written to the underlying stream, but does not flush underlying stream.

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close

public void close()
           throws IOException

Description copied from interface: ObjectOutput

This method closes the underlying stream.

Specified by:

close in interface ObjectOutput

Overrides:

close in class OutputStream

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writeBoolean

public void writeBoolean(boolean data)
                  throws IOException

Description copied from interface: DataOutput

This method writes a Java boolean value to an output stream. If value is true, a byte with the value of 1 will be written, otherwise a byte with the value of 0 will be written. The value written can be read using the readBoolean method in DataInput.

Specified by:

writeBoolean in interface DataOutput

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writeByte

public void writeByte(int data)
               throws IOException

Description copied from interface: DataOutput

This method writes a Java byte value to an output stream. The byte to be written will be in the lowest 8 bits of the int value passed. The value written can be read using the readByte or readUnsignedByte methods in DataInput.

Specified by:

writeByte in interface DataOutput

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writeShort

public void writeShort(int data)
                throws IOException

Description copied from interface: DataOutput

This method writes a Java short value to an output stream. The char to be written will be in the lowest 16 bits of the int value passed. These bytes will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF00) >> 8);
byte1 = (byte)(value & 0x00FF);

The value written can be read using the readShort and readUnsignedShort methods in DataInput.

Specified by:

writeShort in interface DataOutput

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writeChar

public void writeChar(int data)
               throws IOException

Description copied from interface: DataOutput

This method writes a Java char value to an output stream. The char to be written will be in the lowest 16 bits of the int value passed. These bytes will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF00) >> 8);
byte1 = (byte)(value & 0x00FF);

The value written can be read using the readChar method in DataInput.

Specified by:

writeChar in interface DataOutput

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writeInt

public void writeInt(int data)
              throws IOException

Description copied from interface: DataOutput

This method writes a Java int value to an output stream. The 4 bytes of the passed value will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF000000) >> 24);
byte1 = (byte)((value & 0x00FF0000) >> 16);
byte2 = (byte)((value & 0x0000FF00) >> 8);
byte3 = (byte)(value & 0x000000FF);

The value written can be read using the readInt method in DataInput.

Specified by:

writeInt in interface DataOutput

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writeLong

public void writeLong(long data)
               throws IOException

Description copied from interface: DataOutput

This method writes a Java long value to an output stream. The 8 bytes of the passed value will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF00000000000000L) >> 56);
byte1 = (byte)((value & 0x00FF000000000000L) >> 48);
byte2 = (byte)((value & 0x0000FF0000000000L) >> 40);
byte3 = (byte)((value & 0x000000FF00000000L) >> 32);
byte4 = (byte)((value & 0x00000000FF000000L) >> 24);
byte5 = (byte)((value & 0x0000000000FF0000L) >> 16);
byte6 = (byte)((value & 0x000000000000FF00L) >> 8);
byte7 = (byte)(value & 0x00000000000000FFL);

The value written can be read using the readLong method in DataInput.

Specified by:

writeLong in interface DataOutput

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writeFloat

public void writeFloat(float data)
                throws IOException

Description copied from interface: DataOutput

This method writes a Java float value to the stream. This value is written by first calling the method Float.floatToIntBits to retrieve an int representing the floating point number, then writing this int value to the stream exactly the same as the writeInt() method does. The value written can be read using the readFloat method in DataInput.

Specified by:

writeFloat in interface DataOutput

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writeDouble

public void writeDouble(double data)
                 throws IOException

Description copied from interface: DataOutput

This method writes a Java double value to the stream. This value is written by first calling the method Double.doubleToLongBits to retrieve an long representing the floating point number, then writing this long value to the stream exactly the same as the writeLong() method does. The value written can be read using the readDouble method in DataInput.

Specified by:

writeDouble in interface DataOutput

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writeBytes

public void writeBytes(java.lang.String data)
                throws IOException

Description copied from interface: DataOutput

This method writes all the bytes in a String out to the stream. One byte is written for each character in the String. The high eight bits of each character are discarded, thus this method is inappropriate for completely representing Unicode characters.

Specified by:

writeBytes in interface DataOutput

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writeChars

public void writeChars(java.lang.String data)
                throws IOException

Description copied from interface: DataOutput

This method writes all the characters of a String to an output stream as an array of char's. Each character is written using the method specified in the writeChar method.

Specified by:

writeChars in interface DataOutput

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writeUTF

public void writeUTF(java.lang.String data)
              throws IOException

Description copied from interface: DataOutput

This method writes a Java String to the stream in a modified UTF-8 format. First, two bytes are written to the stream indicating the number of bytes to follow. This is written in the form of a Java short value in the same manner used by the writeShort method. Note that this is the number of bytes in the encoded String not the String length. Next come the encoded characters. Each character in the String is encoded as either one, two or three bytes. For characters in the range of
to , one byte is used. The character value goes into bits 0-7 and bit eight is 0. For characters in the range of € to F, two bytes are used. Bits 6-10 of the character value are encoded bits 0-4 of the first byte, with the high bytes having a value of "110". Bits 0-5 of the character value are stored in bits 0-5 of the second byte, with the high bits set to "10". This type of encoding is also done for the null character . This eliminates any C style NUL character values in the output. All remaining characters are stored as three bytes. Bits 12-15 of the character value are stored in bits 0-3 of the first byte. The high bits of the first bytes are set to "1110". Bits 6-11 of the character value are stored in bits 0-5 of the second byte. The high bits of the second byte are set to "10". And bits 0-5 of the character value are stored in bits 0-5 of byte three, with the high bits of that byte set to "10". The value written can be read using the readUTF method in DataInput.

Specified by:

writeUTF in interface DataOutput

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putFields

public ObjectOutputStream.PutField putFields()
                                      throws IOException

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writeFields

public void writeFields()
                 throws IOException

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writeBlockDataHeader

private void writeBlockDataHeader(int size)
                           throws IOException

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findHandle

private java.lang.Integer findHandle(java.lang.Object obj)

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assignNewHandle

private int assignNewHandle(java.lang.Object obj)

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clearHandles

private void clearHandles()

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writeArraySizeAndElements

private void writeArraySizeAndElements(java.lang.Object array,
                                       java.lang.Class clazz)
                                throws IOException

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writeFields

private void writeFields(java.lang.Object obj,
                         ObjectStreamClass osc)
                  throws IOException

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setBlockDataMode

boolean setBlockDataMode(boolean on)
                   throws IOException

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callWriteMethod

private void callWriteMethod(java.lang.Object obj,
                             ObjectStreamClass osc)
                      throws IOException

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getBooleanField

private boolean getBooleanField(java.lang.Object obj,
                                java.lang.Class klass,
                                java.lang.String field_name)
                         throws IOException

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getByteField

private byte getByteField(java.lang.Object obj,
                          java.lang.Class klass,
                          java.lang.String field_name)
                   throws IOException

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getCharField

private char getCharField(java.lang.Object obj,
                          java.lang.Class klass,
                          java.lang.String field_name)
                   throws IOException

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getDoubleField

private double getDoubleField(java.lang.Object obj,
                              java.lang.Class klass,
                              java.lang.String field_name)
                       throws IOException

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getFloatField

private float getFloatField(java.lang.Object obj,
                            java.lang.Class klass,
                            java.lang.String field_name)
                     throws IOException

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getIntField

private int getIntField(java.lang.Object obj,
                        java.lang.Class klass,
                        java.lang.String field_name)
                 throws IOException

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getLongField

private long getLongField(java.lang.Object obj,
                          java.lang.Class klass,
                          java.lang.String field_name)
                   throws IOException

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getShortField

private short getShortField(java.lang.Object obj,
                            java.lang.Class klass,
                            java.lang.String field_name)
                     throws IOException

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getObjectField

private java.lang.Object getObjectField(java.lang.Object obj,
                                        java.lang.Class klass,
                                        java.lang.String field_name,
                                        java.lang.String type_code)
                                 throws IOException

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getField

private java.lang.reflect.Field getField(java.lang.Class klass,
                                         java.lang.String name)
                                  throws InvalidClassException

---

dumpElementln

private void dumpElementln(java.lang.String msg)

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> java >> [ io overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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