Is this raw type assignment type-safe? List = new ArrayList();

Question

I have some code like this:

@SuppressWarnings({\"unchecked\", \"rawtypes\"})
List theList = new ArrayList();

Is this type-saf

Answer 1

The first is type-safe because the list is empty, but still not advised. There's no benefit in using a raw type here. Better to design away from a warning than suppress it.

The second is definitely not type-safe, as theList may be a List<Integer> for example:

import java.util.*;

public class Test {

    public static void main(String[] args) throws Exception {
        List<Integer> integers = new ArrayList<>();
        integers.add(0);

        List<String> strings = new ArrayList(integers);
        // Bang!
        String x = strings.get(0);
    }
}

Note how the constructor itself is called without an exception - there's no way for it to know what kind of list you're really trying to construct, so it doesn't perform any casts. However, when you then fetch a value, that implicitly casts to String and you get a ClassCastException.