Java强制转换方法

Question

I am not sure if this question belongs here. I have written the following method to cast an object to a particular type.

private static <T> T cast(Object obj) {
    return (T) (obj);
}

I am wondering why I do not find such method in Guava or Apache Commons? Am I missing something?

Thanks,

Venk

Answer 1

You can use standart cast method with method

SomeClass o = SomeClass.class.cast(obj);  

No reason to use your method

SomeClass o = Utils.<SomeClass>cast(obj);

Answer 2

Because it is not typesave. Guava in particular is designed to utilize javas static typing to the maximum. With your method it would be possible to cast an object of any class to an object of any other class. This is not supposed to be done.

if you would try the following

Integer a = (Integer) "1";

the compiler would rightfully complain. If you'd use your cast method you would just get rid of the compilation error and postpone the error to runtime. Which is never a good idea. Additionally the compiler warns you that the cast to T is unchecked and may cause problems later on.

In most cases the java type inference is pretty solid and you should listen to compiler warnings.

Reflection on the other hand discards the java type systeme nearly completely. Dealing with this is a little tricky but there are ways to check if types are compatible (eg. Class.isAssignableFrom(Class) ).