Question

In the process of doing some reflection on Java types, I came across an oddity that I do not understand.

Inspecting int for its modifiers returns public, abstract, and final. I understand public and final, but the presence of abstract on a primitive type is non-obvious to me. Why is this the case?

Edit: I am not reflecting on Integer but on int:

import java.lang.reflect.Modifier;

public class IntegerReflection {
    public static void main(final String[] args) {
        System.out.println(String.format("int.class == Integer.class -> %b", int.class == Integer.class));
        System.out.println(String.format("int.class modifiers: %s", Modifier.toString(int.class.getModifiers())));
        System.out.println(String.format("Integer.class modifiers: %s", Modifier.toString(Integer.class.getModifiers())));
    }
}

The output when run:

int.class == Integer.class -> false
int.class modifiers: public abstract final
Integer.class modifiers: public final

Answer 1

If you run

System.out.println(Modifier.toString(int.class.getModifiers()));

you get

public abstract final

possibly because you can’t sub-class it – i.e. final, and you can’t instantiate it – i.e. abstract.

From Oracle’s Abstract Methods and Classes

Abstract classes cannot be instantiated, but they can be subclassed.

The fact is its also final means it cannot be sub-classes.