Why would I use java.lang.Class.cast [duplicate]

Question

I recently stumbled upon a piece of code that went like this:

Object o = .. ;
Foo foo = Foo.class.cast(o);

I was actually not even aware that java.lang.Class had a cast method, so I looked into the docs, and from what I gather this does simply do a cast to the class that the Class object represents. So the code above would be roughly equivalent to

Object o = ..;
Foo foo = (Foo)o;

So I wondered, why I would want to use the cast method instead of simply doing a cast "the old way". Has anyone a good example where the usage of the cast method is beneficial over doing the simple cast?

Answer 1

I don't think it's often used exactly as you have shown. Most common use I have seen is where folks using generics are trying to do the equivalent of this:

public static <T extends Number> T castToNumber(Object o) {
    return (T)o;
}

Which doesn't really do anything useful because of type erasure.

Whereas this works, and is type safe (modulo ClassCastExceptions):

public static <T extends Number> T castToNumber(Object o, Class<T> clazz) {
    return clazz.cast(o);
}

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EDIT: Couple of examples of use from google guava:

• MutableClassToInstanceMap
• Cute use in Throwables#propagateIfInstanceOf, for type safe generic throw spec