string.equals(null) vs string == null

Question

I've seen some of this answered for PHP, SQL and C++, but can't find by java. There is some convention or best practice with that?

I'm asking about null not equals vs ==

if (myString != null && myString == null)

or

if (!myString.equals(null) && myString.equals(null))

Here is the answer I think: http://stackoverflow.com/questions/4501061/java-null-check-why-use-instead-of-equals — marc3l, May 21 '15 at 09:18
It is the answer for your null. Equals will throw a NullPointerException in your case. — marc3l, May 21 '15 at 09:19
if `myString == null`, `myString.equals(null)` throw null pointer .. — Hacketo, May 21 '15 at 09:19
Because if it's `null`, it's like writing `null.equals(null)`. — Maroun, May 21 '15 at 09:22
`foo.equals(null)` has no point because you can't call any method from `null`. So if `foo` is `null` you will end up with calling `null.equals(null)` which throws NPE. — Pshemo, May 21 '15 at 09:23
I don't understand. First one is contradictory, and second one has no sense. Since `myString` would be `null`, you can't apply `equals` to `null` object. — Albert, May 21 '15 at 10:03

score 7 · Accepted Answer · answered May 21 '15 at 09:20

7

mystring == null, if mystring would actually be null it would throw an exception, because you are trying to access its equals method.

answered May 21 '15 at 09:20

Yuri

1

And if you don't want to care about checking null before check a string value , you can do `"astring".equals(myString)` – Hacketo May 21 '15 at 09:27
This answer gives good additional reasons why not to use .equals, even if OP is specifically not asking about it :) https://stackoverflow.com/a/4501084/3255525 – JimLohse Jan 04 '18 at 22:56

score 1 · Answer 2 · answered May 21 '15 at 09:22

1

If myString is not null, myString.equals(null) is false by definition. If it is null, it will throw NullPointerException.

If you want to check whether myString is null, you have to check it by myString == null;

answered May 21 '15 at 09:22

Zereges

score 0 · Answer 3 · answered May 21 '15 at 09:21

0

if (!myString.equals(null) && myString.equals(null))

Would not work as you are attempting to call a method (.equals) on the the none-existent object myString.

answered May 21 '15 at 09:21

3 Answers3