in Java syntax, Class<? extends Something>

Solution 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
}

Solution 2:

You are almost right. Basically, Java has no concept of templates (C++ has). This is called generics. And this defines a generic class Class<> with the generics' attribute being any subclass of Something.

I suggest reading up "What are the differences between “generic” types in C++ and Java?" if you want to get the difference between templates and generics.

Solution 3:

You're right

Definition is that the class has to be subtype of Something

It's the same as Class<T>, but there is a condition that T must extends Something Or implements Something as Anthony Accioly suggested

It can also be class Something itself