Generics Class<? extends Number> explanation

Question

public void foo(Class<? extends Number> value) {
    // compilation error
    processNumber(value);
}

public void processNumber(Number num) {
    // do something about this number.
}

I would like to call "foo" from any subtype of Number (Integer, Double ..etc) Can anyone explain to me how should I do it ?

foo(new Integer(5)); // compilation error 

Answer 1

You are passing a Class object as a value but processNumber takes a Number.

You can use this signature:

public void foo(Number value)

to be able to pass any kind of Number into foo but keep in mind the Liskov Substitution Principle.

As a side note: you don't need foo(new Integer(5)); you can do this instead: foo(5);