Using generic interfaces [duplicate]

Question

This question already has answers here:

What is a raw type and why shouldn't we use it? (16 answers)

Closed 9 years ago.

Is there any differences between those two class declarations

1:

class MyClass <T extends Number & Comparable>

2:

class MyClass <T extends Number & Comparable<T>>

I think that there are differences. But I cannot find an example which would show differences because I don't understand it exact.

Can you show me this example?

Answer 1

There is a difference. The first one is using raw types, and thus, is less type-safe. For example:

This works, but should not work

class MyClass<T extends Number & Comparable>
{
    void use(T t)
    {
        String s = null;
        t.compareTo(s); // Works, but will cause a runtime error
    }
}

Whereas this does not work (because it should not work)

class MyClass<T extends Number & Comparable<T>>
{
    void use(T t)
    {
        String s = null;
        t.compareTo(s); // Compile-time error
    }
}

---

EDIT: Full code, as requested:

class MyClass<T extends Number & Comparable>
{
    void use(T t)
    {
        String s = "Laziness";
        t.compareTo(s); // Works, but will cause a runtime error
    }
}


public class MyClassTest
{
    public static void main(String[] args)
    {
        MyClass<Integer> m = new MyClass<Integer>();
        Integer integer = new Integer(42);
        m.use(integer);
    }
}