Uso de Hash en Java

import java.util.*;

class libro
{
 private Hashtable th = new Hashtable();
 void insert(String name, int code){
  Integer codigo=new Integer(code);
  th.put(name,codigo);
 }
 int ret_code(String name) {
  Integer code=(Integer)th.get((String)name);
  return code.intValue();
 }
}

class test
{
 public static void main (String args[])
 {
 libro lib=new libro();
 lib.insert("Elearning",1);
 lib.insert("Knowledge Management",4);
 lib.insert("Knock the door",8);
 lib.insert("Open your Mind",7);

 System.out.println("Code for Open your Mind: "+
                 lib.ret_code("Open your Mind"));
 }
}