Maps and mutable keys

Foo.java

import java.util.HashMap;
import java.util.Map;

public class Foo {
  static class Mutable {
    int value;

    Mutable(int value) {
      this.value = value;
    }

    @Override
    public int hashCode() {
      return value;
    }

    @Override
    public boolean equals(Object obj) {
      return obj instanceof Mutable && ((Mutable) obj).value == value;
    }
  }

  public static void main(String[] args) {
    Map<Mutable, String> map = new HashMap<Mutable, String>();
    Mutable keyOriginal = new Mutable(1);
    Mutable keyCopy = new Mutable(1);
    map.put(keyOriginal, "a");
    keyOriginal.value = 3;
    System.out.println(map.get(keyCopy));    
  }
}