Java Generics Quiz

Generics1.java

public class Generics1 {

    static class GenType<T> {}
    static class TypeA {}
    static class TypeB extends TypeA {}
    static class TypeC extends TypeB {}

    static <T> void method(GenType<T> arg1, T arg2) {}

    public static void main(String[] args) {
        GenType<TypeA> arg1A = new GenType<>();
        GenType<TypeB> arg1B = new GenType<>();
        GenType<TypeC> arg1C = new GenType<>();
        TypeA arg2A = new TypeA();
        TypeB arg2B = new TypeB();
        TypeC arg2C = new TypeC();

        method(arg1A, arg2A); // stmt 1
        method(arg1A, arg2B); // stmt 2
        method(arg1A, arg2C); // stmt 3

        method(arg1B, arg2A); // stmt 4
        method(arg1B, arg2B); // stmt 5
        method(arg1B, arg2C); // stmt 6

        method(arg1C, arg2A); // stmt 7
        method(arg1C, arg2B); // stmt 8
        method(arg1C, arg2C); // stmt 9
    }
}

Generics2.java

public class Generics2 {

    static class GenType<T> {
        void method1(T arg) {}
        T method2() { return null; }
    }
    static class TypeA {}
    static class TypeB extends TypeA {}
    static class TypeC extends TypeB {}

    static void method(GenType<? extends TypeB> arg) {
        arg.method1(null); // stmt 1
        arg.method1(new Object()); // stmt 2
        arg.method1(new TypeA()); // stmt 3
        arg.method1(new TypeB()); // stmt 4
        arg.method1(new TypeC()); // stmt 5

        Object object = arg.method2(); // stmt 6
        TypeA typeA = arg.method2(); // stmt 7
        TypeB typeB = arg.method2(); // stmt 8
        TypeC typeC = arg.method2(); // stmt 9
    }

    public static void main(String[] args) {
        method(new GenType<Object>()); // stmt 10
        method(new GenType<TypeA>()); // stmt 11
        method(new GenType<TypeB>()); // stmt 12
        method(new GenType<TypeC>()); // stmt 13
    }
}

Generics3.java

/**
 * Same code than Generics2, only the keyword "extends"
 * have been replaced by "super"
 */
public class Generics3 {

    static class GenType<T> {
        void method1(T arg) {}
        T method2() { return null; }
    }
    static class TypeA {}
    static class TypeB extends TypeA {}
    static class TypeC extends TypeB {}

    static void method(GenType<? super TypeB> arg) {
        arg.method1(null); // stmt 1
        arg.method1(new Object()); // stmt 2
        arg.method1(new TypeA()); // stmt 3
        arg.method1(new TypeB()); // stmt 4
        arg.method1(new TypeC()); // stmt 5

        Object object = arg.method2(); // stmt 6
        TypeA typeA = arg.method2(); // stmt 7
        TypeB typeB = arg.method2(); // stmt 8
        TypeC typeC = arg.method2(); // stmt 9
    }

    public static void main(String[] args) {
        method(new GenType<Object>()); // stmt 10
        method(new GenType<TypeA>()); // stmt 11
        method(new GenType<TypeB>()); // stmt 12
        method(new GenType<TypeC>()); // stmt 13
    }
}