Why can't a "Class" variable be passed to instanceof?

Question

Why doesn't this code compile?

    public boolean isOf(Class clazz, Object obj){
        if(obj instanceof clazz){
            return true;
        }else{
            return false;
        }
    }

Why I can't pass a class variable to instanceof?

Answer 1

The instanceof operator works on reference types, like Integer, and not on objects, like new Integer(213). You probably want something like

clazz.isInstance(obj)

---

Side note: your code will be more concise if you write

public boolean isOf(Class clazz, Object obj){
    return clazz.isInstance(obj)
}

Not really sure if you need a method anymore ,though.

Answer 2

instanceof can be used only with explicit class names (stated at compile time). In order to do a runtime check, you should do:

clazz.isInstance(obj)

This has a small advantage over clazz.isAssignableFrom(..) since it deals with the case obj == null better.