hashmap and equals doubts

[naved momin]

i have just one question here regarding equals method
please see the output below

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package hashmapdemo;

import java.util.Collections;
import java.util.Hashtable;

/**
 *
 * @author Admin
 */
public class HashTable {

    /**
     * @param args the command line arguments
     */
    int age;
    String name;

    public HashTable(int ht, String name) {
        this.age = ht;
        this.name = name;
        System.out.println("name = " + name);
    }

    
    
    
    @Override
    public int hashCode() {
         System.out.println("inside hashcode");
        return 7;
    }

    @Override
    public boolean equals(Object obj) {
        if(!(obj instanceof HashTable))
        {
            return false;
        }else if(this == obj)
        {
            return true;
        }
        System.out.println("In equals...");
        System.out.println( (( HashTable ) obj ).name + " " +  this.name );
        
        return ((HashTable)obj).age == this.age && ((HashTable)obj).name == this.name;
    }
//    
    
    public static void main(String[] args) {
        // TODO code application logic here
         java.util.Hashtable table = new Hashtable();
         
         System.out.println("putting hashmap");
         table.put(new HashTable(0,"naved"), "naved momin");
         
         System.out.println("putting hashmap 2");
         table.put(new HashTable(27,"aamir"), "aamir pathan");
         
         
         System.out.println("putting hashmap 3");
         table.put(new HashTable(23, "Priyank1")  , "priyank");
         
         System.out.println("putting hashmap 4");
         table.put(new HashTable(24, "Ankit"), "Ankit nagda");
         
         System.out.println("retreiving value");
         System.out.println("Value = " + " " + table.get(new HashTable(0, "naved")));
         
    }
}

run:
putting hashmap
name = naved
inside hashcode
putting hashmap 2
name = aamir
inside hashcode
In equals...
aamir naved    //"aamir" is the "obj.name" where as "naved" is "this.name"(i suppose this keyword is use to refer to current instance of class , 
//so current instance has name = aamir so why it prints "naved" here  which is a value of previous instance's "name" instance variable ?)
putting hashmap 3
name = Priyank1
inside hashcode
In equals...
Priyank1 aamir
In equals...
Priyank1 naved
putting hashmap 4
name = Ankit
inside hashcode
In equals...
Ankit Priyank1
In equals...
Ankit aamir
In equals...
Ankit naved
retreiving value
name = naved
inside hashcode
In equals...
naved Ankit
In equals...
naved Priyank1
In equals...
naved aamir
In equals...
naved naved
Value =  naved momin
BUILD SUCCESSFUL (total time: 2 seconds)

if you look at the out put carefully and code you will find that value of this.name changes whenever hashmap put's or get's the value thats the only thing left here i m not getting
can any one explain ?

[Ireneusz Kordal]

naved momin wrote:
if you look at the out put carefully and code you will find that value of this.name changes whenever hashmap put's or get's the value thats the only thing left here i m not getting
can any one explain ?

Hi,

follow this link : http://www.docjar.com/html/api/java/util/Hashtable.java.html
This code is an implementation of HashTable in Java.
Look at these lines, this is a way Hastable.put() is implemented:

429       public synchronized V put(K key, V value) {
  430           // Make sure the value is not null
  431           if (value == null) {
  432               throw new NullPointerException();
  433           }
  434   
  435           // Makes sure the key is not already in the hashtable.
  436           Entry tab[] = table;
  437           int hash = key.hashCode();
  438           int index = (hash & 0x7FFFFFFF) % tab.length;
  439           for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {
  440               if ((e.hash == hash) && e.key.equals(key)) {
  441                   V old = e.value;
  442                   e.value = value;
  443                   return old;
  444               }
  445           }

Do you see it ?
All your objects have the same hash value.
So HashTable stores them in the same bucket ( tab[ (hash & 0x7FFFFFFF) % tab.length ] ).
Buckets are implemented as simple arrays.
HashTable loops through all elements of this bucked (array) and for each table element calls it's element.equals( key ) method.

[naved momin]

HashTable loops through all elements of this bucked (array) and for each table element calls it's element.equals( key ) method.

thats why "this.name" always changes when i call

 hashtable.put(key,value);

and "obj.name" remain same ?