import java.util.ArrayList;

class Foo {

    public static class A {}
    public static class B extends A {}
    public static class C extends A {}
    public static class D extends A {}
    public static class E extends B {}
    public static class F extends B {}

    public static void main(String[] args) {
        ArrayList<? extends A> a = new ArrayList<B>();

        System.out.println(a.getClass().getName());
        a.add(new F());
        a.add(new B());
        /*
        Foo.java:16: cannot find symbol
        symbol  : method add(Foo.F)
        location: class java.util.ArrayList<capture#613 of ? extends Foo.A>
                a.add(new F());
                 ^
        Foo.java:17: cannot find symbol
        symbol  : method add(Foo.B)
        location: class java.util.ArrayList<capture#555 of ? extends Foo.A>
                a.add(new B());
                 ^
        */

        System.out.println(a.size());

        return;
    }

}