Integer extends Number but can't operate on with Integer

Question

Integer extends Number so why do I get the error at the bottom?

interface Predicate<T> {
   public abstract boolean check(T t);
}

Predicate<? extends Number> predUpper = null;

predUpper.check(new Integer(73));

Error: The method check(capture#6-of ? extends Number) in the type Predicate is not applicable for the arguments (Integer)

I have read: Method in the type Map<String,capture#1-of ? extends Object> is not applicable and Difference between <? super T> and <? extends T> in Java

Answer 1

Since the Predicate will consume the Integer, you should do:

Predicate<? super Integer> predUpper //Solution 1

or just:

Predicate<Number> predUpper //Solution 2

There's difference, however, in these approaches:

• The type-parameter <? super Integer from "Solition 1" represents a whole family of super-types of Integer (including Integer).

• The type-parameter <Number> from "Solution 2" represents a sub-class of the Number interface. Since Integer is such, it's applicable here.

More info:

• What is PECS?