为什么用Java编译？

Question

Why does this compile?

B is used in A without any generic parameters, and this compiled in Java. What is going on here?

interface B<T>
{
    public T Foo(T value);
}

public class A
{
    public B What()
    {
        return null;
    }

    public void Foo()
    {
        B x = What();
        x.Foo(123);
    }
}

Answer 1

This is for compatibility with pre-J2SE 5.0 Java. You should get a rawtypes warning (take notice of the compiler warnings).

Answer 2

You're just using a raw type of B here. Just like

 List list = new ArrayList(); // defined as: public interface List<E>

Perfectly, valid; not recommended though.