StringBuffer class in java

import java.util.*;

class strbuf1
{
        public static void main(String args[])
       {
              StringBuffer s1 = new StringBuffer();
              StringBuffer s2 = new StringBuffer("Hello World");
              StringBuffer s3 = new StringBuffer(s2);
              StringBuffer s4 = new StringBuffer(100);
              System.out.println("s1 = " + s1);
              System.out.println("s2 = " + s2);
              System.out.println("s3 = " + s3);
              System.out.println("s1.length = " + s1.length());
              System.out.println("s2.length = " + s2.length());
              System.out.println("s3.length = " + s3.length());
              System.out.println("s4.length = " + s4.length());
              System.out.println("s1.capacity = " + s1.capacity());
              System.out.println("s2.capacity = " + s2.capacity());
              System.out.println("s3.capacity = " + s3.capacity());
              System.out.println("s4.capacity = " + s4.capacity());
     }
}