how to check if an object's property is null

Question

I'm trying to check whether a property is null, but I get a null pointer exception. What's the right way to do this?

private void recursePrintList(myNode head)
{
    if(head.next == null) //NullPointerException on this line
    {
        System.out.println(head.value);
    }
    else
    {
        System.out.println(head.value);
        recursePrintList(head.next);
    }
}

If `head` is null, then `head.next` will throw a `NullPointerException` — Powerlord, Mar 23 '15 at 17:17
possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — fabian, Mar 23 '15 at 17:17

score 5 · Answer 1 · answered Mar 23 '15 at 17:16

You have to check if head is null at the start of your method. Also you can further simplify your recursive print:

private void recursePrintList(myNode head) {
    if (head != null) {
        System.out.println(head.value);
        recursePrintList(head.next);
    }
}

score 0 · Answer 2 · answered Mar 23 '15 at 17:51

0

You should check the value of head as if null is not equal to head then do the operations.

ivate void recursePrintList(myNode head) { if ( null != head) { System.out.println(head.value); recursePrintList(head.next); } }

answered Mar 23 '15 at 17:51

Rahul Vashishta

184
2
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how to check if an object's property is null

2 Answers2