Mixing Generics and Legacy code question

[Rahul Spark]

import java.util.ArrayList;
import java.util.List;

public class Test {
	public static void main(String[] args) {
		List<Integer> intList = new ArrayList<Integer>();
		append(intList);
                System.out.println(intList.get(0));
	}
	public static void append(List list) {
		list.add("hello");
	}
}

Output: hello

I understand that Legacy List can add any Object. But after coming out of function, why

List<Integer>

is able to get String and print out (while it is

List<Integer>

)


[HENRY: enabled code tags]

[Henry Wong]

As you already noticed, don't mix generics with non-generics -- generics can break.

Henry

[Rahul Spark]

Thanks. Can you please explain why it is not giving ClassCastException while printing String from List<Integer>?

My question is more for certification point of view and for better understanding this. Thanks again.

[Stephan van Hulst]

The compiler expects to retrieve an Integer, for which the PrintWriter has no special method, so the compiler chooses the println() method that has the Object argument, which works equally well for the String retrieved.

[Rahul Spark]

Thanks Stephan

Infact below code gave ClassCastException

Integer i = intList.get(0); // ClassCastException

[Stephan van Hulst]

Yes, because it tries to cast the reference to an Integer, which it's clearly not.

In the former case, it casts the reference to an Object. This is perfectly fine.