why it result in a NullPointerException when Object is null?

Question

when objec is null:

if(object != null && object.string.equals("")) {
    System.out.println("no error");
}

it will result in NullPointerException, and why if it checks the first result is false, it still check the second instead of stop check and print "no error"? sorry for my bad english -_-#

I think Java isn't using a lazy evaluation like some other languages, it will check to whole condition before choosing the answer true/false. — Lutzi, Apr 25 '18 at 10:02
@Lutzi The `&&` operator _is_ short-circuiting (i.e. lazy). But an 'AND' condition will evaluate the second half if the first half is true. That's what it means. — nbrooks, Apr 25 '18 at 10:04
&& only evaluates the right side if the left side is true. Very clearly defined in the JLS. — Thorbjørn Ravn Andersen, Apr 25 '18 at 10:04
@Lutzi No. `&&` and `||` are short-circuiting operators just as in C++ and C and Lisp where the McCarthy operators came from in the first place. — user207421, Apr 25 '18 at 10:16
@nbrooks Thanks for the precision ! So `&&` and `AND` are not equivalent ? Sorry for my bad comment, but it's really a pleasure to interact with other Java programmers ! I'll try to check my answer better than that. — Lutzi, Apr 25 '18 at 10:17

score 3 · Answer 1 · answered Apr 25 '18 at 10:03

3

It's not object which is null but object.string.

Try: (object != null && "".equals(object.string))

answered Apr 25 '18 at 10:03

Grzegorz Piwowarek

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thank you, and I find my mistake : before I take a judgement, I'm already Obeject object = new Obeject(); thank you for your answer again – 史书恒 Apr 26 '18 at 01:34

why it result in a NullPointerException when Object is null?

1 Answers1