6.4.2 Terminal Symbols and Constants

The following symbols in java.io.ObjectStreamConstants define the terminal and constant values expected in a stream.

    final static short STREAM_MAGIC = (short)0xaced;
    final static short STREAM_VERSION = 5;
    final static byte TC_NULL = (byte)0x70;
    final static byte TC_REFERENCE = (byte)0x71;
    final static byte TC_CLASSDESC = (byte)0x72;
    final static byte TC_OBJECT = (byte)0x73;
    final static byte TC_STRING = (byte)0x74;
    final static byte TC_ARRAY = (byte)0x75;
    final static byte TC_CLASS = (byte)0x76;
    final static byte TC_BLOCKDATA = (byte)0x77;
    final static byte TC_ENDBLOCKDATA = (byte)0x78;
    final static byte TC_RESET = (byte)0x79;
    final static byte TC_BLOCKDATALONG = (byte)0x7A;
    final static byte TC_EXCEPTION = (byte)0x7B;
    final static byte TC_LONGSTRING = (byte) 0x7C;
    final static byte TC_PROXYCLASSDESC = (byte) 0x7D;
    final static  int   baseWireHandle = 0x7E0000;

The flag byte classDescFlags may include values of

    final static byte SC_WRITE_METHOD = 0x01; //if SC_SERIALIZABLE
     final static byte SC_BLOCK_DATA = 0x08;    //if SC_EXTERNALIZABLE
    final static byte SC_SERIALIZABLE = 0x02;
    final static byte SC_EXTERNALIZABLE = 0x04;

The flag SC_WRITE_METHOD is set if the Serializable class writing the stream had a writeObject method that may have written additional data to the stream. In this case a TC_ENDBLOCKDATA marker is always expected to terminate the data for that class.

The flag SC_BLOCKDATA is set if the Externalizable class is written into the stream using STREAM_PROTOCOL_2. By default, this is the protocol used to write Externalizable objects into the stream in JDK^TM 1.2. JDK^TM 1.1 writes STREAM_PROTOCOL_1.

The flag SC_SERIALIZABLE is set if the class that wrote the stream extended java.io.Serializable but not java.io.Externalizable, the class reading the stream must also extend java.io.Serializable and the default serialization mechanism is to be used.

The flag SC_EXTERNALIZABLE is set if the class that wrote the stream extended java.io.Externalizable, the class reading the data must also extend Externalizable and the data will be read using its writeExternal and readExternal methods.

Example

Consider the case of an original class and two instances in a linked list:

class List implements java.io.Serializable {
    int value;
    List next;
    public static void main(String[] args) {
        try {
            List list1 = new List();
            List list2 = new List();
            list1.value = 17;
            list1.next = list2;
            list2.value = 19;
            list2.next = null;

            ByteArrayOutputStream o = new ByteArrayOutputStream();
            ObjectOutputStream out = new ObjectOutputStream(o);
            out.writeObject(list1);
            out.writeObject(list2);
            out.flush();
            ...
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

The resulting stream contains:

00: ac ed 00 05 73 72 00 04 4c 69 73 74 69 c8 8a 15 >....sr..Listi...<

10: 40 16 ae 68 02 00 02 49 00 05 76 61 6c 75 65 4c >Z......I..valueL<

20: 00 04 6e 65 78 74 74 00 06 4c 4c 69 73 74 3b 78 >..nextt..LList;x<

30: 70 00 00 00 11 73 71 00 7e 00 00 00 00 00 13 70 >p....sq.~......p<

40: 71 00 7e 00 03                                  >q.~..<