java.util.IdentityHashMap writeObject(ObjectOutputStream s) when called
is throwning:
java.io.NotActiveException: defaultWriteObject

Test program and output is as below:
 
import java.util.*;
import java.io.*;
 
 
public class Test extends IdentityHashMap {
   public static final int SIZE=100;
   public static Test t =null;
  
   public static void main(String [] arg) {
        t = new Test();
        String key = "key";
        String value = "value";
        for (int i=0; i < SIZE; i++) {
             String newKey = key + i;
             String newValue = value + i;
             t.put(newKey,newValue);
        }
        t.TestMethod();
   }
   
    void TestMethod() {
        try {
            FileOutputStream wstream = new FileOutputStream("TestFile.ser");
ObjectOutputStream wfile = new ObjectOutputStream(wstream);
            t.writeObject(wfile);
  wfile.close();
            System.out.println("write over");

       } catch (Exception e) {
           e.printStackTrace();
       }
    }
     
 }
 ------------------------------output result-----------------
 H:\merlin\dev\testbase\src\libs_api_tests\common\java_util\IdentityHashMap\IdentityHashMapTest2>java -version
java version "1.4.0beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0beta-b41)
Java HotSpot(TM) Client VM (build B41, mixed mode)

H:\merlin\dev\testbase\src\libs_api_tests\common\java_util\IdentityHashMap\IdentityHashMapTest2>java Test
java.io.NotActiveException: defaultWriteObject
        at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:474)
        at java.util.IdentityHashMap.writeObject(IdentityHashMap.java:1007)
        at Test.TestMethod(Test.java:26)
        at Test.main(Test.java:19)