genericExtendAndSuper

genericExtendAndSuper.java

        List<? extends Number> extendsList = null;
        List<? super Number> superList = null;

        List<Object> objList = null;
        List<Number> numberList = null;
        List<Integer> integerList = null;

        //extendsList=objList; //compile error
        extendsList = numberList;
        extendsList = integerList;

        superList = objList;
        superList = numberList;
        //superList = integerList; //compile error

        Object obj = null;
        Number num = null;
        Integer integer = null;

        //extend 适合读取，因为不能添加
        //super 适合添加，因为读取出来是Object类型

        //extendsList.add(obj); // compile error
        //extendsList.add(num);//compile error
        //extendsList.add(integer);//compile error

        //superList.add(obj);//compile error
        superList.add(num);
        superList.add(integer);


        Number number = extendsList.get(0);
        Object object = superList.get(0);