获取通用变量的参数化类型类

Question

public class Foo {

    public <T> void foo(final T t) {
        final Class<T> clazz = (Class<T>) t.getClass();
    }

}

I can not understand why t.getClass() return a Class<?> and not a Class<T> (or a Class<? extends T> ) and so why I need to make a cast.

In which way this cast can fail ?

Answer 1

Generics in Java is implemented using type erasure.

The type T does not exist at runtime and the compiler substitutes the T with java.lang.Object . So the following method is actually compiled in bytecode:

public void foo(final Object t)

Answer 2

You should look up the term 'type erasure'. The way Java does generics is to compile 'generic' code. That is, it compiles code that will work with any type and does the type checking at compile time.