The following program:

import java.util.*;

class Test {

    public static void main(List<String> args) {
        main(new ArrayList<String>());
    }
}


Will show a warning telling the user that a dimaond operator could be used. The warning will be displayed regardless of the source level - on the other hand, while it's ok to use diamond in JDK 8 (thanks to improved type inference) it's not ok to do so in JDK 7.