getClass() of a Generic Method Parameter in a Java

Question

The following Java method fails to compile:

 void foo(T t)
{
    Class klass = t.getClass();
}

Error

Answer 1

It is kind of silly. It would have been better, for most use cases, if x.getClass() returns Class, instead of the erased Class.

The erasure is the cause of loss of information, making your code, apparently safe, fail to compile. t.getClass() returns Class, and |T| = Number, so it returns Class.

The erasure (mandated by the language spec) is to maintain theoretical correctness. For example

List x = ...;
Class c1 = x.getClass(); // ok
Class> c2 = x.getClass(); // error

Although c2 seems very reasonable, in Java, there is really no such class for List. There is only the class for List. So allowing c2 would be, theoretically incorrect.

This formality created lots of problem in real world usages, where programmers can reason that Class is safe for their purposes, but have to cope with the erased version.

You can simply define your own getClass that returns the un-erased type

static public  Class getFullClass(X x)
    return (Class)(Class) x.getClass() ;

 void foo(T t)
{
    Class klass = getFullClass(t);
}