what is the different between string and stringbuilder in the code? : <p>i would like to know why the output of this code is "roar roar!!!" not "roar!!! roar!!!"?
the code is:</p>

<pre><code> public class Lion 
 {
   public void roar(String roar1, StringBuilder roar2) {
   roar1.concat("!!!");
   roar2.append("!!!");
 }
 public static void main(String[] args)
{
  String roar1 = "roar";
  StringBuilder roar2 = new StringBuilder("roar");
  new Lion().roar(roar1, roar2);
  System.out.println(roar1 + " " + roar2);
} }
</code></pre>

<p>i try to find the reason of method concat() dont appends one String to the end of another. please with explain. </p>
