Can one compare java.lang.Class objects with == in Java?

Question

Possible Duplicate:
Does Java guarantee that Object.getClass() == Object.getClass()?

If I have a class such as

Class<? extends MyObject> aClass = ...;

can I then do:

if (aClass == MySubObject.class) { ... }

or do I have to do

if (aClass.equals(MySubObject.class)) { ... }

In addition, further to knowing the answer, I would love to know a reference i.e. where this is defined.

I prefer to use == if possible, because I find it more readable, and faster. (Obviously it's not that much more readable, or that much faster, but still, why use a more complex solution if a simpler solution is available.)

http://stackoverflow.com/questions/3738919/does-java-guarantee-that-object-getclass-object-getclass — Wojciech Owczarczyk, Jan 17 '12 at 14:46
Another one http://stackoverflow.com/questions/928531/does-java-have-an-is-kind-of-class-test-method — Carl Winder, Jan 17 '12 at 14:47
http://stackoverflow.com/questions/5997801/java-comparing-classes-with-or-equals-is-there-a-difference — Wojciech Owczarczyk, Jan 17 '12 at 14:47

score 7 · Accepted Answer · answered Jan 17 '12 at 14:48

7

You can use == but you gain nothing because that's exactly what Class.equals() does.

Class doesn't define an equals method, so it inherits from Object. You can read the source to see this.

I use equals where possible as then I don't need to think about it. When I am reading code (including my code) I still don't need to ask myself is == the same as equals or not for this class.

answered Jan 17 '12 at 14:48

Peter Lawrey

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5

Yes, you gain something: `==` is null safe. – yankee Sep 09 '13 at 15:06
5

@yankee true, in which case you could write. `MySubObject.class.equals(aClass)` – Peter Lawrey Sep 09 '13 at 15:09

score 5 · Answer 2 · answered Jan 17 '12 at 14:48

You can compare classes with ==, and that's the same thing as equals for the case of Class, but your example suggests that you want to know whether one class has an "is-a" relationship with another. Two classes are only equal if they're the same class, and clearly Vehicle.class != Car.class.

If you want to know whether a Car is-a Vehicle, use Class#isAssignableFrom.

Can one compare java.lang.Class objects with == in Java?

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