Java.util.Hashmap doesn't work for a custom object

Question

Hi,
i have created a class named ID. I am trying to test it on a Hashmap, but the the "containsKey" and "get" operations do not work. Every operation of the main method returns as if the ID objects have not been inserted. Ideas?
package swarm.sys.id;
import java.util.*;
import java.io.*;
import swarm.sys.common.*;
import swarm.sys.interfaces.*;
public class ID implements IDInterface, Cloneable, Serializable
    String type;
    int body;
    String id;
    private static int idCounter=0;
    public ID(String type, int body)
      this.type=type;
      this.body=body;
      id=type+Ids.padWithZeroes(body);
    public String getType()
      return type;
    }//getType
    public String getBody()
      return Ids.padWithZeroes(body);
    }//getBody
    public int getIntBody()
      return body;
    }//getIntBody
    public boolean equals(Object o)
      if (!(o instanceof ID))
        return false;
      else
          ID id=(ID)o;   
          return (this.getType().equals(id.getType()) && 
                  this.getIntBody()==id.getIntBody());        
    }//equals
    /* factory method, which produces new IDs and afterwards
     * increments the body part
    public static ID newID(String type)
        return new ID(type,idCounter++);
    }//newID
    //implements deep cloning
    public Object clone()
        return new ID(new String(this.type),this.body);
    }//clone
    public String toString()
      return id.trim();
    }//toString
    public static void main(String[] args)
        Hashtable<IDInterface,String> table=new Hashtable<IDInterface,String>();
        table.put(new ID("PEER_",1),"x1");
        table.put(new ID("PEER_",2),"x1");
        table.put(new ID("PEER_",3),"x2");
        table.put(new ID("PEER_",4),"x3");
        table.put(new ID("PEER_",5),"x3");
        ID id1=new ID("PEER_",1);
        ID id14=new ID("PEER_",14);       
        System.out.println("table.containsKey(new ID(PEER_,1)): "+table.containsKey(id1)); //should be true
        System.out.println("table.containsKey(new ID(PEER_,14)): "+table.containsKey(id14)); //should be false
        System.out.println("table.get(new ID(PEER_,1))"+table.get(id1)); //should be x1
}

Answer 1

You need to override the hashCode() method.
http://www.javapractices.com/Topic28.cjp