When does a NullPointerException occurs?

[Charley Wu]

1 String s = null;
2 if ( s != null & s.length() > 0)
3 System.out.println("s != null & s.length() > 0");
4 if ( s != null && s.length() > 0)
5 System.out.println("s != null & s.length() > 0");
6 if ( s != null | | s.length() > 0)
7 System.out.println("s != null & s.length() > 0");
8 if ( s != null | s.length() > 0)
9 System.out.println("s != null | s.length() > 0");
Why line 2,6,8 give the NullPointerException while line 4 not?
Thanks

[Jane Griscti]

Hi Charley,
Line 4 is not giving the error as you are using the 'short circuit' && operator. This operator returns 'true' only if both arguments are true. Since the first argument 's != null' is false, it doesn't bother checking the second argument. As the argument is not evaluated, no NullPointerException is raised.
Hope that helps.
------------------
Jane
The cure for boredom is curiosity.
There is no cure for curiosity.
-- Dorothy Parker
[This message has been edited by Jane Griscti (edited December 03, 2000).]