Question

My code is as follows

package com.foo;

public class TestComposition {
    public static void main(String[] args) {
        try {
            Class<Foo> fooClass = 
                    (Class<Foo>) Class.forName("Foo");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

The assignment within the ‘try’ block results in a warning stating

Type safety: Unchecked cast from Class<capture#1-of ?> to 
     Class<Foo>

Why is this?

Answer 1

Well, to start with let’s be clear where the problem is – it’s in the cast itself. Here’s a shorter example:

public class Test {    
    public static void main(String[] args) throws Exception {
        Object x = (Class<Test>) Class.forName("Test");
    }
}

This still has the same problem. The issue is that the cast isn’t actually going to test anything – because the cast will be effectively converted to the raw Class type. For Class<T> it’s slightly more surprising because in reality the object does know the class involved, but consider a similar situation:

List<?> list = ... get list from somewhere;
List<String> stringList = (List<String>) list;

That cast isn’t going to check that it’s really a List<String>, because that information is lost due to type erasure.

Now in your case, there’s actually a rather simpler solution – if you know the class name at compile-time anyway, just use:

Class<Foo> fooClass = Foo.class;

If you can provide a more realistic example where that’s not the case, we can help you determine the most appropriate alternative.