diff --git a/classpath/java/io/ObjectInputStream.java b/classpath/java/io/ObjectInputStream.java
index d0adaf0ad5..d12fcd127a 100644
--- a/classpath/java/io/ObjectInputStream.java
+++ b/classpath/java/io/ObjectInputStream.java
@@ -2,9 +2,11 @@ package java.io;
 
 public class ObjectInputStream extends InputStream {
   private final InputStream in;
+  private final Reader r;
 
   public ObjectInputStream(InputStream in) {
     this.in = in;
+    this.r = new PushbackReader(new InputStreamReader(in));
   }
 
   public int read() throws IOException {
@@ -18,4 +20,257 @@ public class ObjectInputStream extends InputStream {
   public void close() throws IOException {
     in.close();
   }
+
+  public Object readObject() throws IOException {
+    return readObject(new HashMap());
+  }
+
+  public boolean readBoolean() throws IOException {
+    read('z');
+    return readLongToken() != 0;
+  }
+
+  public byte readByte() throws IOException {
+    read('b');
+    return (byte) readLongToken();
+  }
+
+  public char readChar() throws IOException {
+    read('c');
+    return (char) readLongToken();
+  }
+
+  public short readShort() throws IOException {
+    read('s');
+    return (short) readLongToken();
+  }
+
+  public int readInt() throws IOException {
+    read('i');
+    return (int) readLongToken();
+  }
+
+  public long readLong() throws IOException {
+    read('j');
+    return readLongToken();
+  }
+
+  public float readFloat() throws IOException {
+    read('f');
+    return (float) readDoubleToken();
+  }
+
+  public double readDouble() throws IOException {
+    read('d');
+    return readDoubleToken();
+  }
+
+  private void skipSpace() throws IOException {
+    int c;
+    while ((c = r.read()) != -1 && Character.isSpace((char) c));
+    if (c != -1) {
+      r.unread(c);
+    }
+  }
+
+  private void read(char v) throws IOException {
+    skipSpace();
+
+    int c = r.read();
+    if (c != v) {
+      if (c == -1) {
+        throw new EOFException();
+      } else {
+        throw new StreamCorruptedException();
+      }
+    }
+  }
+
+  private String readStringToken() throws IOException {
+    skipSpace();
+
+    StringBuilder sb = new StringBuilder();
+    int c;
+    while ((c = r.read()) != -1 && ! Character.isSpace((char) c)) {
+      sb.append((char) c);
+    }
+    if (c != -1) {
+      r.unread(c);
+    }
+    return sb.toString();
+  }
+
+  private long readLongToken() throws IOException {
+    return Long.parseLong(readStringToken());
+  }
+
+  private double readDoubleToken() throws IOException {
+    return Double.parseDouble(readStringToken());
+  }
+
+  private Object readObject(HashMap<Integer, Object> map) throws IOException {
+    skipSpace();
+    switch (r.read()) {
+    case 'a':
+      return deserializeArray(map);
+    case 'l':
+      return deserialize(map);
+    case 'n':
+      return null;
+    case -1:
+      throw new EOFException();
+    default:
+      throw new StreamCorruptedException();
+    }
+  }
+
+  private Object deserializeArray(HashMap<Integer, Object> map)
+    throws IOException
+  {
+    read('(');
+    int id = (int) readLongToken();
+    Class c = Class.forName(readStringToken());
+    int length = (int) readLongToken();
+    Object o = Array.newInstance(c.getComponentType(), length);
+
+    map.put(id, o);
+  
+    for (int i = 0; i < length; ++i) {
+      skipSpace();
+    
+      switch (r.read()) {
+      case 'a':
+        Array.set(o, i, deserializeArray(map));
+        break;
+
+      case 'l':
+        Array.set(o, i, deserialize(map));
+        break;
+
+      case 'r':
+        Array.set(o, i, map.get((int) readLongToken()));
+        break;
+
+      case 'n':
+        Array.set(o, i, null);
+        break;
+
+      case 'z':
+        f.setBoolean(o, readLongToken() != 0);
+        break;
+
+      case 'b':
+        f.setByte(o, (byte) readLongToken());
+        break;
+
+      case 'c':
+        f.setChar(o, (char) readLongToken());
+        break;
+
+      case 's':
+        f.setShort(o, (short) readLongToken());
+        break;
+
+      case 'i':
+        f.setInt(o, (int) readLongToken());
+        break;
+
+      case 'j':
+        f.setLong(o, readLongToken());
+        break;
+
+      case 'f':
+        f.setFloat(o, (float) readDoubleToken());
+        break;
+
+      case 'd':
+        f.setDouble(o, readDoubleToken());
+        break;
+
+      case -1:
+        throw new EOFException();
+
+      default:
+        throw new StreamCorruptedException();
+      }
+    }
+
+    read(')');
+  }
+
+  private Object deserialize(HashMap<Integer, Object> map)
+    throws IOException
+  {
+    read('(');
+    int id = (int) readLongToken();
+    Class c = Class.forName(readStringToken());
+    Object o = c.newInstance();
+
+    map.put(id, o);
+  
+    for (Field f: c.getFields()) {
+      int modifiers = f.getModifiers();
+      if ((modifiers & (Modifier.TRANSIENT | Modifier.STATIC)) == 0) {
+        skipSpace();
+    
+        switch (r.read()) {
+        case 'a':
+          Array.set(o, i, deserializeArray(map));
+          break;
+
+        case 'l':
+          Array.set(o, i, deserialize(map));
+          break;
+
+        case 'r':
+          Array.set(o, i, map.get((int) readLongToken()));
+          break;
+
+        case 'n':
+          Array.set(o, i, null);
+          break;
+
+        case 'z':
+          Array.setBoolean(o, i, readLongToken() != 0);
+          break;
+
+        case 'b':
+          Array.setByte(o, i, (byte) readLongToken());
+          break;
+
+        case 'c':
+          Array.setChar(o, i, (char) readLongToken());
+          break;
+
+        case 's':
+          Array.setShort(o, i, (short) readLongToken());
+          break;
+
+        case 'i':
+          Array.setInt(o, i, (int) readLongToken());
+          break;
+
+        case 'j':
+          Array.setLong(o, i, readLongToken());
+          break;
+
+        case 'f':
+          Array.setFloat(o, i, (float) readDoubleToken());
+          break;
+
+        case 'd':
+          Array.setDouble(o, i, readDoubleToken());
+          break;
+
+        case -1:
+          throw new EOFException();
+
+        default:
+          throw new StreamCorruptedException();
+        }
+      }
+    }
+
+    read(')');
+  }
 }
diff --git a/classpath/java/io/ObjectOutputStream.java b/classpath/java/io/ObjectOutputStream.java
index 9a57d10bcd..a771b8e000 100644
--- a/classpath/java/io/ObjectOutputStream.java
+++ b/classpath/java/io/ObjectOutputStream.java
@@ -1,10 +1,12 @@
 package java.io;
 
+import java.util.IdentityHashMap;
+
 public class ObjectOutputStream extends OutputStream {
-  private final OutputStream out;
+  private final PrintStream out;
 
   public ObjectOutputStream(OutputStream out) {
-    this.out = out;
+    this.out = new PrintStream(out);
   }
   
   public void write(int c) throws IOException {
@@ -22,5 +24,157 @@ public class ObjectOutputStream extends OutputStream {
   public void close() throws IOException {
     out.close();
   }
+
+  public void writeObject(Object o) throws IOException {
+    writeObject(o, new IdentityHashMap(), 0);
+  }
+
+  public void writeBoolean(boolean v) {
+    out.print("z");
+    out.print((v ? 1 : 0));
+  }
+
+  public void writeByte(byte v) {
+    out.print("b");
+    out.print((int) v);
+  }
+
+  public void writeChar(char v) {
+    out.print("c");
+    out.print((int) v);
+  }
+
+  public void writeShort(short v) {
+    out.print("s");
+    out.print((int) v);
+  }
+
+  public void writeInt(int v) {
+    out.print("i");
+    out.print(v);
+  }
+
+  public void writeLong(long v) {
+    out.print("j");
+    out.print(v);
+  }
+
+  public void writeFloat(float v) {
+    out.print("f");
+    out.print(v);
+  }
+
+  public void writeDouble(double v) {
+    out.print("d");
+    out.print(v);
+  }
+
+  private void writeObject(Object o, IdentityHashMap<Object, Integer> map,
+                           int nextId)
+    throws IOException
+  {
+    if (o == null) {
+      out.print("n");
+    } else {
+      Integer id = map.get(new Identity(o));
+      if (id == null) {
+        map.put(new Identity(o), nextId);
+
+        Class c = o.getClass();
+        if (c.isArray()) {
+          serializeArray(o, map, nextId);
+        } else if (Serializable.class.isAssignableFrom(c)) {
+          serialize(o, map, nextId);
+        } else {
+          throw new NotSerializableException(c.getName());
+        }
+      } else {
+        out.print("r");
+        out.print(id.intValue());
+      }
+    }
+  }
+
+  private void serializeArray(Object o, IdentityHashMap<Object, Integer> map,
+                              int nextId)
+    throws IOException
+  {
+    Class c = o.getClass();
+    Class t = c.getComponentType();
+    int length = Array.getLength(o);
+
+    out.print("a(");
+    out.print(nextId++);
+    out.print(" ");
+    out.print(c.getName());
+    out.print(" ");
+    out.print(length);
+
+    for (int i = 0; i < length; ++i) {
+      out.print(" ");
+      if (t.equals(boolean.class)) {
+        writeBoolean(Array.getBoolean(o));
+      } else if (t.equals(byte.class)) {
+        writeByte(Array.getByte(o));
+      } else if (t.equals(char.class)) {
+        writeChar(Array.getChar(o));
+      } else if (t.equals(short.class)) {
+        writeShort(Array.getShort(o));
+      } else if (t.equals(int.class)) {
+        writeInt(Array.getInt(o));
+      } else if (t.equals(long.class)) {
+        writeLong(Array.getLong(o));
+      } else if (t.equals(float.class)) {
+        writeFloat(Array.getFloat(o));
+      } else if (t.equals(double.class)) {
+        writeDouble(Array.getDouble(o));
+      } else {
+        writeObject(Array.get(o), map, nextId);
+      }
+    }
+
+    out.print(")");
+  }
+  
+  private void serialize(Object o, IdentityHashMap<Object, Integer> map,
+                         int nextId)
+    throws IOException
+  {
+    Class c = o.getClass();
+
+    out.print("l(");
+    out.print(nextId++);
+    out.print(" ");
+    out.print(c.getName());
+
+    for (Field f: c.getFields()) {
+      int modifiers = f.getModifiers();
+      if ((modifiers & (Modifier.TRANSIENT | Modifier.STATIC)) == 0) {
+        out.print(" ");
+        Class t = f.getType();
+        if (t.equals(boolean.class)) {
+          writeBoolean(f.getBoolean(o));
+        } else if (t.equals(byte.class)) {
+          writeByte(f.getByte(o));
+        } else if (t.equals(char.class)) {
+          writeChar(f.getChar(o));
+        } else if (t.equals(short.class)) {
+          writeShort(f.getShort(o));
+        } else if (t.equals(int.class)) {
+          writeInt(f.getInt(o));
+        } else if (t.equals(long.class)) {
+          writeLong(f.getLong(o));
+        } else if (t.equals(float.class)) {
+          writeFloat(f.getFloat(o));
+        } else if (t.equals(double.class)) {
+          writeDouble(f.getDouble(o));
+        } else {
+          writeObject(f.get(o), map, nextId);
+        }
+      }
+    }
+
+    out.print(")");
+  }
   
 }
diff --git a/classpath/java/util/HashMap.java b/classpath/java/util/HashMap.java
index c7f129d786..8c859da55e 100644
--- a/classpath/java/util/HashMap.java
+++ b/classpath/java/util/HashMap.java
@@ -3,17 +3,17 @@ package java.util;
 public class HashMap<K, V> implements Map<K, V> {
   private int size;
   private Cell[] array;
-  private final CellFactory factory;
+  private final Helper helper;
 
-  HashMap(int capacity, CellFactory<K, V> factory) {
+  HashMap(int capacity, Helper<K, V> helper) {
     if (capacity > 0) {
       array = new Cell[nextPowerOfTwo(capacity)];
     }
-    this.factory = factory;
+    this.helper = helper;
   }
 
   public HashMap(int capacity) {
-    this(capacity, new MyCellFactory());
+    this(capacity, new MyHelper());
   }
 
   public HashMap() {
@@ -30,14 +30,6 @@ public class HashMap<K, V> implements Map<K, V> {
     return size;
   }
 
-  private static int hash(Object a) {
-    return (a == null ? 0 : a.hashCode());
-  }
-
-  private static boolean equal(Object a, Object b) {
-    return (a == null && b == null) || (a != null && a.equals(b));
-  }
-
   private void resize() {
     if (array == null || size >= array.length * 2) {
       resize(array == null ? 16 : array.length * 2);
@@ -115,7 +107,7 @@ public class HashMap<K, V> implements Map<K, V> {
   private Cell<K, V> putCell(K key, V value) {
     Cell<K, V> c = find(key);
     if (c == null) {
-      insert(factory.make(key, value, null));
+      insert(helper.make(key, value, null));
     } else {
       V old = c.getValue();
       c.setValue(value);
@@ -196,11 +188,15 @@ public class HashMap<K, V> implements Map<K, V> {
     public void setNext(HashMap.Cell<K, V> next);
   }
 
-  interface CellFactory<K, V> {
+  interface Helper<K, V> {
     public Cell<K, V> make(K key, V value, Cell<K, V> next);
+    
+    public int hash(K key);
+
+    public boolean equal(K a, K b);
   }
 
-  private static class MyCell<K, V> implements Cell<K, V> {
+  private class MyCell<K, V> implements Cell<K, V> {
     public final K key;
     public V value;
     public Cell<K, V> next;
@@ -232,14 +228,22 @@ public class HashMap<K, V> implements Map<K, V> {
     }
 
     public int hashCode() {
-      return (key == null ? 0 : key.hashCode());
+      return helper.hash(key);
     }
   }
 
-  private static class MyCellFactory<K, V> implements CellFactory<K, V> {
+  static class MyHelper<K, V> implements Helper<K, V> {
     public Cell<K, V> make(K key, V value, Cell<K, V> next) {
       return new MyCell(key, value, next);
     }
+
+    public int hash(K a) {
+      return (a == null ? 0 : a.hashCode());
+    }
+
+    public boolean equal(K a, K b) {
+      return (a == null && b == null) || (a != null && a.equals(b));
+    }
   }
 
   private class EntrySet implements Set<Entry<K, V>> {
diff --git a/classpath/java/util/IdentityHashMap.java b/classpath/java/util/IdentityHashMap.java
new file mode 100644
index 0000000000..be58d2eee9
--- /dev/null
+++ b/classpath/java/util/IdentityHashMap.java
@@ -0,0 +1,65 @@
+package java.util;
+
+public class IdentityHashMap<K, V> implements Map<K, V> {
+  private final HashMap<K, V> map;
+
+  public IdentityHashMap(int capacity) {
+    map = new HashMap(capacity, new MyHelper());
+  }
+
+  public IdentityHashMap() {
+    this(0);
+  }
+
+  public int size() {
+    return map.size();
+  }
+
+  public boolean containsKey(K key) {
+    return map.containsKey(key);
+  }
+
+  public boolean containsValue(V value) {
+    return map.containsValue(value);
+  }
+
+  public V get(K key) {
+    return map.get(key);
+  }
+
+  public V put(K key, V value) {
+    return map.put(key, value);
+  }
+
+  public V remove(K key) {
+    return map.remove(key);
+  }
+
+  public void clear() {
+    map.clear();
+  }
+
+  public Set<Entry<K, V>> entrySet() {
+    return map.entrySet();
+  }
+
+  public Set<K> keySet() {
+    return map.keySet();
+  }
+
+  public Collection<V> values() {
+    return map.values();
+  }
+
+  private static class MyHelper<K, V>
+    extends HashMap.MyHelper<K, V>
+  {
+    public int hash(K a) {
+      return (a == null ? 0 : System.identityHashCode(a));
+    }
+
+    public boolean equal(K a, K b) {
+      return a == b;
+    }    
+  }
+}
diff --git a/classpath/java/util/WeakHashMap.java b/classpath/java/util/WeakHashMap.java
index 340acb6d90..5fb18bf615 100644
--- a/classpath/java/util/WeakHashMap.java
+++ b/classpath/java/util/WeakHashMap.java
@@ -9,7 +9,7 @@ public class WeakHashMap<K, V> implements Map<K, V> {
   private final ReferenceQueue queue;
 
   public WeakHashMap(int capacity) {
-    map = new HashMap(capacity, new MyCellFactory());
+    map = new HashMap(capacity, new MyHelper());
     queue = new ReferenceQueue();
   }
 
@@ -111,8 +111,8 @@ public class WeakHashMap<K, V> implements Map<K, V> {
     }
   }
 
-  private static class MyCellFactory<K, V>
-    implements HashMap.CellFactory<K, V>
+  private static class MyHelper<K, V>
+    extends HashMap.MyHelper<K, V>
   {
     public HashMap.Cell<K, V> make(K key, V value, HashMap.Cell<K, V> next) {
       return new MyCell(key, value, next);