Why does String.valueOf(Object obj) == null return false when argument obj is null? [duplicate]

Question

public static void main(String[] args) {
  Long lo = null;
  System.out.println(String.valueOf(lo) == null);
}

Why the above statement return false ? Can anyone please explain..

We use "equals()" method to check equality for objects (String in this case), not "==". — Aakash
– Aakash, Commented May 19, 2016 at 3:49
@aakash you don't use equals() to check for null. It would never return false. — shmosel
– shmosel, Commented May 20, 2016 at 0:47
@shmosel I never said that you use equals() to check for null. Please read my comment again. Certainly there were some gaps in my comment, which I thought could be easily filled by OP's understanding of Java. String.valueOf(lo) would return a string "null", which is not null. So, if OP wants to check that, he should have used String.valueOf(lo).equals("null"). And as this is already answered by you, congrats. — Aakash
– Aakash, Commented May 20, 2016 at 3:48
@Aakash I think OP thought String.valueOf(null) returns null. In other words, he wasn't attempting to compare strings altogether. — shmosel
– shmosel, Commented May 20, 2016 at 3:53

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

Read the Javadoc:

Returns:

if the argument is null, then a string equal to "null"; otherwise, the value of obj.toString() is returned.

In other words, the result is the string "null", not the value null.

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answered May 19, 2016 at 2:50

shmosel

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