Write a Program in Java for Immutable string

Immutable string: 

Immutable string means no-changeable after manipulating in the program.

Program code:

public class HelloWorld{
public static void main(String args[]){
String s="Heera";
s.concat("Babu");//concat() method appends the string at the end
System.out.println(s);
}
}

Sample Output:

Since, Here two objects are created but s reference variable, therefore use reference variable assignment.
if further code is changes as:

public class HelloWorld{

     public static void main(String args[]){  
   String s="Heera";  
   s=s.concat("Babu");//concat() method appends the string at the end  
   System.out.println(s); 
 }  
}  

then output: