ObjectInputStream deserializes objects, arrays, and other values from a stream that was previously created with an ObjectOutputStream. The readObject( ) method deserializes objects and arrays (which should then be cast to the appropriate type); various other methods read primitive data values from the stream. Note that only objects that implement the Serializable or Externalizable interface can be serialized and deserialized.

A class may implement its own private readObject(ObjectInputStream) method to customize the way it is deserialized. If you define such a method, there are several ObjectInputStream methods you can use to help deserialize the object. defaultReadObject( ) is the easiest. It reads the content of the object just as an ObjectInputStream would normally do. If you wrote additional data before or after the default object contents, you should read that data before or after calling defaultReadObject( ). When working with multiple versions or implementations of a class, you may have to deserialize a set of fields that do not match the fields of your class. In this case, give your class a static field named serialPersistentFields whose value is an array of ObjectStreamField objects that describe the fields to be deserialized. If you do this, your readObject( ) method can call readFields( ) to read the specified fields from the stream and return them in a ObjectInputStream.GetField object. See ObjectStreamField and ObjectInputStream.GetField for more details. Finally, you can call registerValidation( ) from a custom readObject( ) method. This method registers an ObjectInputValidation object (typically the object being deserialized) to be notified when a complete tree of objects has been deserialized, and the original call to the readObject( ) method of the ObjectInputStream is about to return to its caller.

The remaining methods include miscellaneous stream-manipulation methods and several protected methods for use by subclasses that want to customize the deserialization behavior of ObjectInputStream.

Figure 9-36. java.io.ObjectInputStream

public class ObjectInputStream extends InputStream implements ObjectInput, 
     ObjectStreamConstants {
// Public Constructors
     public ObjectInputStream(InputStream in) throws IOException;  
// Protected Constructors
1.2  protected ObjectInputStream( ) throws IOException, SecurityException;  
// Nested Types
1.2  public abstract static class GetField; 
// Public Instance Methods
     public void defaultReadObject( ) throws IOException, ClassNotFoundException;  
1.2  public ObjectInputStream.GetField readFields( ) throws IOException, 
     ClassNotFoundException;  
1.4  public Object readUnshared( ) throws IOException, ClassNotFoundException;  
     public void registerValidation(ObjectInputValidation obj, int prio) throws 
     NotActiveException, InvalidObjectException;  
// Methods Implementing DataInput
     public boolean readBoolean( ) throws IOException;  
     public byte readByte( ) throws IOException;  
     public char readChar( ) throws IOException;  
     public double readDouble( ) throws IOException;  
     public float readFloat( ) throws IOException;  
     public void readFully(byte[ ] buf) throws IOException;  
     public void readFully(byte[ ] buf, int off, int len) throws IOException;  
     public int readInt( ) throws IOException;  
     public long readLong( ) throws IOException;  
     public short readShort( ) throws IOException;  
     public int readUnsignedByte( ) throws IOException;  
     public int readUnsignedShort( ) throws IOException;  
     public String readUTF( ) throws IOException;  
     public int skipBytes(int len) throws IOException;  
// Methods Implementing ObjectInput
     public int available( ) throws IOException;  
     public void close( ) throws IOException;  
     public int read( ) throws IOException;  
     public int read(byte[ ] buf, int off, int len) throws IOException;  
     public final Object readObject( ) throws IOException, ClassNotFoundException;  
// Protected Instance Methods
     protected boolean enableResolveObject(boolean enable) throws SecurityException;  
1.3  protected ObjectStreamClass readClassDescriptor( ) throws IOException, 
     ClassNotFoundException;  
1.2  protected Object readObjectOverride( ) throws IOException, 
     ClassNotFoundException;     constant
     protected void readStreamHeader( ) throws IOException, StreamCorruptedException;  
     protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException, 
     ClassNotFoundException;  
     protected Object resolveObject(Object obj) throws IOException;  
1.3  protected Class<?> resolveProxyClass(String[ ] interfaces) throws IOException, 
     ClassNotFoundException;  
// Deprecated Public Methods
#    public String readLine( ) throws IOException;              Implements:DataInput
}