为什么try-catch不会在未经检查的泛型强制转换中解决警告？

Question

Consider the following MCVE :

public class MyClass {
    private LinkedList<Foo> myList = new LinkedList<Foo>();

    // Some irrevelant stuff which includes loading myList

    public void myMethod() {
        LinkedList<Foo> newList;

        try {
             newList = (LinkedList<Foo>) myList.clone();
        } catch (ClassCastException e) {
             // do something in case java screws up
        }
    }
}

I know that you can get rid of the warning by using @SuppressWarnings("unchecked") but why doesn't the try/catch block work? Is it a waste of time and energy to put the try/catch in there?

Answer 1

That won't work, because you are not getting a ClassCastException for this.

The erased type of the list cannot be checked at runtime.

You might get a ClassCastException when you try to get something out of the List (and that turns out not to be a Foo), but the List itself is just a LinkedList (without knowing what its element types can be).

An instance of LinkedList<Foo> looks exactly like a LinkedList<Bar> at runtime.

The reason for the warning is that the runtime system cannot guarantee that the cast you are doing is correct (it can check the LinkedList part, but not the generic type).

Answer 2

I think that when you are explicitly casting anything, the compiler doesn't check for unchecked exceptions. The compiler relies on the code writer for explicit type casting.

Answer 3

- Erasure is a process in which the Type Parameters and Arguments are removed from the Class within and the methods,etc.

- Box<String> becomes Box , this is known as Raw Type , where the Generic classes and interfaces are stripped off their Type Arguments during the Compile time,

- And this is done so that during Run time a back ward compatibility can be obtained to those codes which doesn't used the Generics .

So thats the reason this is going unchecked.