JAVA: adding and removing elements from a defined variable within a class : I'm trying to get this class to run but I keep running into issues. I'm new to Java and not sure if I am doing this correctly. If someone could just help me out with the addition of elements to a list I can figure out the rest!

    class ListPractice implements Testable {

    def mylist = [4,5,6]

    /**
     * Adds a set of elements to the mylist variable
     *
     * @param elts The elements to be added
     */
    def addToList(List elts) {

        def newlist = getMylist()+List
        return newlist
    }

    @Override
    void testMe() {
        addToList([7,8,9])
        assert  getMylist() == [4,5,6,7,8,9]
        assert  getMylist() == [7,8,9]
    }
}