List list = new ArrayList();
List list1 = new ArrayList<Object>();
List list2 = new ArrayList<Integer>();

List list = new ArrayList();
list.add(111);
list.add(222);

List<Integer> list1 = list;

list1.forEach(System.out::println);

Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
    at java.util.ArrayList.forEach(ArrayList.java:1249)
    at code.TestDemo.main(TestDemo.java:16)

List list = new ArrayList();
List<Object> list2 = list;

List<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);
list.add(3);

List<?> list2 = list;
list2.remove(0);
list2.clear();

List<Integer> list1 = new ArrayList<>();
List<Number> list2 = new ArrayList<>();
List<? extends Number> list = list1;
list = list2;

List<Integer> list1 = new ArrayList<>();
list1.add(1);
list1.add(2);

List<? extends Number> list = list1;
list.add(null);

List<Integer> list1 = new ArrayList<>();
list1.add(1);
list1.add(2);

List<? extends Number> list = list1;
Number number = list.get(0);
Object number1 = list.get(0);

List<Integer> list1 = new ArrayList<>();
List<Number> list2 = new ArrayList<>();

List<? super Integer> list = list1;
list = list2;

List<Integer> list1 = new ArrayList<>();
List<? super Integer> list = list1;
list.add(new Integer(1));

List<Object> list1 = new ArrayList<>();
list1.add(new Animal());
list1.add(new Person());
list1.add(new Man());

List<? super Man> list = list1;
Object obj = list1.get(1);