generics - in Java syntax, Class<? extends Something>

Question

Class<? extends Something>

Here's my interpretation, it's class template but the class ? means the name of the class is undetermined and it extends the Something class.

if there's something wrong with my interpretation, let me know.

Answer 1

There are a few confusing answers here so I will try and clear this up. You define a generic as such:

public class Foo<T> {
    private T t;
    public void setValue(T t) {
        this.t = t;
    }
    public T getValue() {
        return t;
    }
}

If you want a generic on Foo to always extend a class Bar you would declare it as such:

public class Foo<T extends Bar> {
    private T t;
    public void setValue(T t) {
        this.t = t;
    }
    public T getValue() {
        return t;
    }
}

The ? is used when you declare a variable.

Foo<? extends Bar>foo = getFoo();

OR

DoSomething(List<? extends Bar> listOfBarObjects) {
    //internals
}