How to determine an object's class?

Question

If class B and class C extend class A and I have an object of type B or C, how can I determine of which type

Answer 1

Multiple right answers were presented, but there are still more methods: Class.isAssignableFrom() and simply attempting to cast the object (which might throw a ClassCastException).

Possible ways summarized

Let's summarize the possible ways to test if an object obj is an instance of type C:

// Method #1
if (obj instanceof C)
    ;

// Method #2
if (C.class.isInstance(obj))
    ;

// Method #3
if (C.class.isAssignableFrom(obj.getClass()))
    ;

// Method #4
try {
    C c = (C) obj;
    // No exception: obj is of type C or IT MIGHT BE NULL!
} catch (ClassCastException e) {
}

// Method #5
try {
    C c = C.class.cast(obj);
    // No exception: obj is of type C or IT MIGHT BE NULL!
} catch (ClassCastException e) {
}

Differences in null handling

There is a difference in null handling though:

• In the first 2 methods expressions evaluate to false if obj is null (null is not instance of anything).
• The 3rd method would throw a NullPointerException obviously.
• The 4th and 5th methods on the contrary accept null because null can be cast to any type!

To remember: null is not an instance of any type but it can be cast to any type.

Notes

• Class.getName() should not be used to perform an "is-instance-of" test becase if the object is not of type C but a subclass of it, it may have a completely different name and package (therefore class names will obviously not match) but it is still of type C.
• For the same inheritance reason Class.isAssignableFrom() is not symmetric:
  obj.getClass().isAssignableFrom(C.class) would return false if the type of obj is a subclass of C.