Why does Class.getSuperclass() sometimes return Object.class?

Question

According to the Class.getSuperclass() documentation:

Returns the Class representing the superclass of the entity (class, interface, primitive type or void) represented by this Class. If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned.

But I'm sometimes seeing Object.class being returned (using jdk1.7.0_45) - so am having to check for it separately:

final Class<?> superclass = modelClass.getSuperclass();
if ((superclass != null) && (Object.class != superclass)) {
     // Do stuff with superclasses other than Object.
}

Is this a Java bug? Is there a better way of checking whether superclass is an Object?

Answer 1

The documentation says that if your class is java.lang.Object, then its getSuperclass is going to return null. In other words, if you do this

Class objSuper = Object.class.getSuperclass();

then objSuper would be null; this is precisely what's happening (demo).

It appears, however, that your modelClass is not java.lang.Object, and it is also not a primitive or an interface. Therefore, returning java.lang.Object makes perfect sense, because all classes implicitly inherit from it.

Answer 2

The this Class in the documentation is referring to the caller of the getSuperclass() method as far as I understand it.

So if the caller is either the Object class or a primitive type / interface the superclass returned will be null which makes total sense in my opinion.

Answer 3

If you need to find out if Object is a direct parent of your class, you can use

System.out.println(YourObject.class.getSuperclass() == Object.class);

Otherwise you should know that at the end each object inherits Object class. Instead of Object class itself, so .getSuperclass() will return null.