Java Programming

Hi,
I learned concept of StringBuilder but when I am trying this in my computer I found some errors which I post here in particular line commented.

public class StringBuilder {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		StringBuilder sb = new StringBuilder(); // creates empty builder, capacity 16
		sb.append("Greetings");  // The method append(String) is undefined for the type StringBuilder(adds 9 character string at beginning)


		int l = sb.length(); //The method length() is undefined for the type StringBuilder
		System.out.print("length is "+l);


	}

}

I tried with java 1.5 and java 1.6 aswell.
Pl tell anybody if know what is problem.

thanks,
Shobhit