java help

i need help with java 

this is the question 

Complete the code to counts the number of lines input by a user until the user enters the string ENDOFDATA (must be uppercase letters, no spaces) on a line by itself. Make sure you display the number of lines found. Use the nextLine() method of Scanner class to read entire lines of data. (Hint, this is like counting the number of integers entered, but reading Strings and using String comparison to check for equality).

String SENTINEL = "ENDOFDATA";
Scanner keyboard = new Scanner(System.in);
System.out.println( "Enter lines of data or " + SENTINEL + " to quit" );