What does it mean isInstance is a 'dynamic equivalent' of instanceof?

Question

What does it mean 'dynamic equivalent'?

I just wonder what is the purpose of having this.getClass().isInstance(aClass) instead of this instanceof aClass? Is there a difference?

Determines if the specified Object is assignment-compatible with the object represented by this Class. This method is the dynamic equivalent of the Java language instanceof operator

Answer 1

Yes. Not only is the order not the same, but object instanceof Clazz must have a class which is known at compile time. clazz.isInstance(object) can take a class which is known at runtime.

There is also subtle difference in that isInstance will auto-box, but instanceof will not.

e.g.

10 instanceof Integer // does not compile
Integer.class.isInstance(10) // returns true

Integer i = 10;
if (i instanceof String) // does NOT compile
if (String.class.isInstance(i)) // is false

To see the difference I suggest you try to use them.

Note: if you do object.getClass().getClass() or myClass.getClass() you will just get a Class Be careful not to call getClass() when you don't need to.

Answer 2

The instanceof operator tests to see if an object is an instance of a fixed (static) class; i.e. a class whose name is known at compile time.

The Class.isInstance method allows you to test against a dynamic class; i.e. a class that is only known at runtime.

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I just wonder what is the purpose of having this.getClass().isInstance(aClass) instead of this instanceof aClass? Is there a difference?

The purpose of isInstance is as above.

The primary difference between those two expressions is:

• in the first one, aClass is a variable whose value is a Class object, and

• in the second one, aClass is the name of a class: it CANNOT be a variable.