String Buffer Program in Java

import java.io.*;

public class stringBuffer{
    public static void main(String[] args) throws Exception{
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String str;
        try{
            System.out.print("Enter your name: ");
            str = in.readLine();
            str += ", This is the example of SringBuffer class and it's functions.";

            //Create a object of StringBuffer class
            StringBuffer strbuf = new StringBuffer();
            System.out.print(strbuf.length());
            strbuf.append(str);
            System.out.println(strbuf);
            strbuf.delete(0,str.length());

            //append()
            strbuf.append("Hello");
            strbuf.append("World");                         //print HelloWorld
            System.out.println(strbuf);

            //insert()
            strbuf.insert(5,"_Java ");                      //print Hello_Java World
            System.out.println(strbuf);

            //reverse()
            strbuf.reverse();
            System.out.print("Reversed string : ");
            System.out.println(strbuf);                     //print dlroW avaJ_olleH
            strbuf.reverse();
            System.out.println(strbuf);                     //print Hello_Java World

            //setCharAt()
            strbuf.setCharAt(5,' ');
            System.out.println(strbuf);                     //prit Hello Java World

            //charAt()
            System.out.print("Character at 6th position : ");
            System.out.println(strbuf.charAt(6));           //print J

            //substring()
            System.out.print("Substring from position 3 to 6 : ");
            System.out.println(strbuf.substring(3,7));      //print lo J

            //deleteCharAt()
            strbuf.deleteCharAt(3);
            System.out.println(strbuf);                     //print Helo java World

            //capacity()
            System.out.print("Capacity of StringBuffer object : ");
            System.out.println(strbuf.capacity());          //print 21

            //delete() and length()
            strbuf.delete(6,strbuf.length());
            System.out.println(strbuf);                     //no anything
        }
        catch(StringIndexOutOfBoundsException e){
            System.out.println(e.getMessage());
        }
    }
}