Java Excellant Program

How to get all keys from HashMap

package com.java2novice.hashmap;

import java.util.HashMap;

import java.util.Set;

public class MyHashMapKeys

{

public static void main(String a[])

{

        HashMap hm = new HashMap();

        hm.put("first", "First inserted");

        hm.put("second", "Second inserted");

        hm.put("third","Third inserted");

        System.out.println(hm);

        Set keys = hm.keySet();

        for(String key: keys)

        {

            System.out.println(key);

        }

    }

}

How to get entry set from HashMap

package com.java2novice.hashmap;

import java.util.HashMap;

import java.util.Map.Entry;

import java.util.Set;

public class MyHashMapEntrySet

{

public static void main(String a[])

{

        HashMap hm = new HashMap();

        hm.put("first", "First inserted");

        hm.put("second", "Second inserted");

        hm.put("third","Third inserted");

        System.out.println(hm);

        Set> entires = hm.entrySet();

        for(Entry ent:entires)

        {

            System.out.println(ent.getKey()+" ==> "+ent.getValue());

        }

    }

}

How to delete all elements from HashMap

package com.java2novice.hashmap;

import java.util.HashMap;

public class MyHashMapClear

{

 public static void main(String a[])

{

        HashMap hm = new HashMap();

        hm.put("first", "First inserted");

        hm.put("second", "Second inserted");

        hm.put("third","Third inserted");

        System.out.println("My HashMap content:");

        System.out.println(hm);

        System.out.println("Clearing HashMap:");

        hm.clear();

        System.out.println("Content After clear:");

        System.out.println(hm);

    }

}

How to eliminate duplicate user defined objects as a key from HashMap

package com.java2novice.hashmap;

import java.util.HashMap;

import java.util.Set;

public class MyDuplicateKeyEx

{

public static void main(String a[])

{

        HashMap hm = new HashMap();

        hm.put(new Price("Banana", 20), "Banana");

        hm.put(new Price("Apple", 40), "Apple");

        hm.put(new Price("Orange", 30), "Orange");

        printMap(hm);

        Price key = new Price("Banana", 20);

        System.out.println("Adding duplicate key...");

        hm.put(key, "Grape");

        System.out.println("After adding dulicate key:");

        printMap(hm);

    }

    public static void printMap(HashMap map)

    {

        Set keys = map.keySet();

        for(Price p:keys)

        {

            System.out.println(p+"==>"+map.get(p));

        }

    }

}

class Price

{

    private String item;

    private int price;

public Price(String itm, int pr)

{

        this.item = itm;

        this.price = pr;

 }

public int hashCode()

 {

        int hashcode = 0;

        hashcode = price*20;

        hashcode += item.hashCode();

        return hashcode;

    }

  public boolean equals(Object obj)

 {

        if (obj instanceof Price)

       {

            Price pp = (Price) obj;

            return (pp.item.equals(this.item) && pp.price == this.price);

        }

        else

        {

            return false;

        }

    }

  public String getItem()

 {

        return item;

  }

 public void setItem(String item)

    {

        this.item = item;

    }

    public int getPrice()

    {

        return price;

    }

    public void setPrice(int price)

   {

        this.price = price;

    }

    public String toString()

    {

        return "item: "+item+"  price: "+price;

    }

}