String builder v/s String in Java

Through this program you can determine the effeciency of string and string builder . which is more efficient for use in java program.

//  Demo program for string v/s string builder

import java.util.*;
 class stringbuilder{

       public static void main(String[] arg)

       {
           long now = System.currentTimeMillis();
          fast();
          System.out.println("fast elapsed "+(System.currentTimeMillis()-now)+"ms");
          now = System.currentTimeMillis();
         slow();
        System.out.println("slow elapsed "+(System.currentTimeMillis()-now)+"ms");
     }
 private static void fast(){
    StringBuilder s=new StringBuilder();
    for(int i=0;i<=10000;i++)
    {
        s.append("*");
    }
 }
  private static void slow(){
     String  s=new String();
     for(int i=0;i<=10000;i++)
     {
         s+="*";
     }
  }
}