Using equals() in if statement to check for nullability

Question

I have an if statement which is returning a NullPointerException.

Object obj;
if (obj.toString().equals("string"))

The expected result is a NullPointerException as obj has no value assigned to it, and it's being compared to a String.

Now considering the condition below

Object obj;
if (obj.toString().equals(null))

obj still being null (as I haven't assigned a value to it), although shouldn't my if statement return as true since obj is being compared to null?

hmm .. this looks like you might be mis-using the toString - the general rule is to never-ever override it for application reasons, so generally there is no need to check its return value. There are odd corner cases, though :) — kleopatra, Dec 01 '21 at 12:35

score 2 · Accepted Answer · edited Sep 19 '21 at 09:55

2

You need to explicitly check against the literal value null. In the following example, if the non-null check fails, it wont' run the statement after the &&; the first check short-circuits the rest of the expression

Object obj;
if (obj != null && obj.toString().equals("string")) { 
  //do something 
}
else { 
  //do another something 
}

Note:

null is a literal value (similar to true and false). So you should not be comparing it like a String.

edited Sep 19 '21 at 09:55

K450

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answered Sep 19 '21 at 04:57

djsumdog

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obj.toString.equals("string") doesn't compile – tgdavies Sep 19 '21 at 05:05
@tgdavies good catch. Edited the answer to include the function call. – djsumdog Sep 19 '21 at 05:07

Using equals() in if statement to check for nullability

1 Answers1

Note: