Question

The wrapper class Integer has the static method parseInt() which is used like this:

Integer.parseInt();

I thought only methods of static classes could be called like this (i.e. Class.doMethod()). All non-static classes need objects to be instantiated to use their methods.

I checked the API, and apparently Integer is declared as public final Integer – not static.

Answer 1

Any class can contain both static and non-static methods. When calling the static methods on any class – including your own – you don’t need to instantiate an instance of the class, just call the method using the class name: MyClass.methodName().

In fact, even the following will work:

Integer nullInt = null;
nullInt.parseInt("5");

This works because only the class type of the reference is important when calling static methods. But consider this poor style: always use e.g. Integer.parseInt instead.

Also note that you can’t declare a top-level class as static anyway: only nested/inner classes can be declared as static.