How to write program Map interface in collection ?

import java.util.*;
public class Where
{
    public static void main(String args[])
    {
   HashMap h=new HashMap();
      h.put(111, "ram");
           h.put(112, "neha");
    h.put(113, "hem");
     h.put(114, "sallu");
      Set s=h.entrySet();
      Iterator it=s.iterator();
      while(it.hasNext())
      {
     Map.Entry me=(Map.Entry)it.next();
        System.out.println("me.getKey():" +me.getKey());
        System.out.println("me.getValue():" +me.getValue());
       
        }   
   System.out.println();
}   
}   

output:-

for compile-
E:\sallu>javac Where.java
for run-
E:\sallu>java Where
me.getKey():114
me.getValue():sallu
me.getKey():113
me.getValue():hem
me.getKey():112
me.getValue():neha
me.getKey():111
me.getValue():ram


E:\sallu>

Difference between StringBuffer, String and StringBuilder in Java

1) String is immutable while StringBuffer and StringBuilder is mutable object.

2) StringBuffer is synchronized while StringBuilder is not which makes StringBuilder faster than StringBuffer.

3) Concatenation operator "+" is internal implemented using either StringBuffer or StringBuilder.

4) Use String if you require immutability, use Stringbuffer in java if you need mutable + thread-safety and use StringBuilder in Java if you require mutable + without thread-safety.