4

There is a possiblity that this may be a dupicate question. I initialize a String variable to null.I may or may not update it with a value.Now I want to check whether this variable is not equal to null and whatever I try I get a null pointer exception.I can't afford to throw nullpointer exception as it is costly.Is there any workaround that is efficient.TIA

Thorbjørn Ravn Andersen
  • 73,784
  • 33
  • 194
  • 347

5 Answers5

3

If you use

if (x == null)

you will not get a NullPointerException.

I suspect you're doing:

if (x.y == null)

which is throwing because x is null, not because x.y is null.

If that doesn't explain it, please post the code you're using to test for nullity.

Jon Skeet
  • 1,421,763
  • 867
  • 9,128
  • 9,194
  • Ya you got it right.I have the variable y declared as null in X class.However X is not null.No exception is thrown for non null values –  Aug 14 '09 at 12:58
  • 1
    If `x` is not null, then `if (x.y == null)` will not throw a `NullPointerException`. – Jon Skeet Aug 14 '09 at 12:59
  • X cannot be null because I am passing X.z to another function as parameter just before this line which is not throwing null pointer exception –  Aug 14 '09 at 13:02
3

I guess you are doing something like this,

  String s = null;

  if (s.equals(null))

You either check for null like this

  if (s == null)

A better approach is to ignore the null and just check for the expected value like this,

  if ("Expected value".equals(s))

In this case, the result is always false when s is null.

ZZ Coder
  • 74,484
  • 29
  • 137
  • 169
1

String is immutable 

@Test(expected = NullPointerException.class)
public void testStringEqualsNull() {
    String s = null;
    s.equals(null);
}

@Test
public void testStringEqualsNull2() {
    String s = null;
    TestCase.assertTrue(s == null);
}
Paul McKenzie
  • 19,646
  • 25
  • 76
  • 120
1

I am comparing s==null only

can you show the code snippet that you have written s==null will never throw a NPE

Asif
  • 11
  • 2
  • You are right...The reason for the exception was I was originally comparing s!=null||s.equals("") and the or part was throwing nullpointerException.However I removed that but forgot to restart the server.Thanks for ur responses –  Aug 17 '09 at 02:42
0

if you are checking whether "s" is null, then do not apply a dot(.) after "s". Doing that would throw NullPOinterException, as applying dot(.) means that you are trying to access on a pointer location which is basically null at the moment !

Also try to use library functions that check whether a string is null or empty. you may use StringUtils.isEmpty(s) from apache library which checked both

Saptarshi Misra
  • 11
  • 1