Java: how to tell if an object is of a specific subclass

Question

Java: how to tell if an object is of a specific subclass.

I want to have a check to see if an object is of a particular subclass and have the check NOT come back true for other classes that have inherited from the same superclass.

So, for example:

superclass: fruit

subclass: apple and banana extend fruit

Then I have a check (if appleObject.isThisClass(apple)) {do stuff}

So far all I've been able to find are ways to check that will still return true because they share the same superclass.

Hopefully that makes sense.

Thanks for the help.

Please look over this tutorial on polymorphism. Performing a check like this is almost certainly the wrong approach. — ajb
– ajb, Commented Apr 12, 2014 at 2:10

Elliott Frisch · Accepted Answer · 2014-04-12 03:43:31Z

Assuming you have an object reference apple of type Banana or Apple; then something like this,

if (apple instanceof Apple) // true

tells you if apple is of type Apple. Where as

if (apple instanceof Banana) // false

Would exclude Banana and finally

if (apple instanceof Fruit) // true

would include Banana or Apple; but you should probably not be testing this in callers (tight coupling) - instead, you should try and encapsulate behavior in the Fruit "interface".

EDIT

Given your additional question in the comment,

Fruit aFruit = aMethod(); // get a fruit. if (aFruit instanceof Apple) { Apple apple = (Apple) aFruit; // do apple things with the apple. apple.somethingOnlyApplesDo(); } // else if (aFruit instanceof Banana) { // Do Nothing With Bananas. // Banana banana = (Banana) aFruit; // }

if the 'appleObject' is actually a subclass of 'Apple' the appleObject instanceof Apple will also return true.
Is there a way to test this though: if (apple instanceof Apple) // true if (apple instanceof Fruit) // FALSE ?
@user3448228 Not using instanceof. Because every apple is also a fruit! You can call getClass(), but again - this is not a good idea, because it is very "tight coupling".
@user3448228 What are you actually trying to achieve with this?
I have a method that returns a fruit (it could be either an apple or a banana depending). So, basically: fruit aFruit = aMethod(); Then I have an if statement that does a check on aFruit and if it is an apple stuff happens and if it is a banana nothing happens. Hopefully that makes sense. Its possible I just set all of this up in a bad way (still learning).

Colin D · Accepted Answer · 2014-04-12 02:18:01Z

Use the getClass() method that is inherited from Object.

http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#getClass%28%29

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