What's the best way to check for not null values in java.
String query ="abcd";
query != null vs !query.equals(null).
which is better?why?
4 Answers
1st one is better (and the only option), because 2nd one will throw NPE, when your value is actually null. As simple as that.
Try this out:
String str = null;
str.equals(null); // will throw `NPE`.
So basically, the test which you wanted to perform itself triggers a NullPointerException in the 2nd case. So, it is no choice.
9 Comments
Jesse Webb
NPE = NullPointerException for those who don't know the acronym
Cratylus
@RohitJain:I did:
String test = "aa"; System.out.println(test.equals(null));.Prints falseJesse Webb
@Cratylus - now try it with
String test = null; and see what happens...
PermGenError
@Cratylus what rohit meant was to try
String s= null; s.equals(null)
Rohit Jain
@Cratylus. Why would he test for
non-null if there is no possibility of null value at all? And if there is a possibility of null value, then there is NPE in 2nd case. |
!str.equals(null) will
- always return false if it does not throw an exception, and
- throw an exception if str is null
The point of a null check is to make sure the reference, in this code str, actually refers to an object. If it is null, you can't call any methods on it, including equals, without throwing a NullPointerException... which the point of null checks is to avoid happening.
So !str.equals(null) causes the very problem null checks are meant to prevent and doesn't do what you think at all. Never do this.
1 Comment
PermGenError
+1, i made the same point about
str.equals(null) would always return false, but my answer not clear about the concrete question.. :)query != null better as !query.equals(null) will throw an exception when query is actually null. Also query != null is easily readable
Comments
query != null compares if the object is null. query.equals("something") compares the value inside of that object. string == "something". so in this case use query != null.
Stringobjects too?Stringwhich aren't objects? There is no primitive equivalent as far as I know...