A, java in the List and ArrayList
List is an interface, there are a lot of implementation classes such as: ArrayList, LinkedList, Vector with which it is new which
ArrayList is an implementation of the List interface inherits and implements the interface List
List a = new ArrayList();
Two, List.add () and List.addAll () method
1, List.addAll: Add the list each element to the current list of
List a = new ArrayList();
a.add(1);
a.add(2);
a.add(3);
List b = new ArrayList();
b.add(4);
b.add(5);
b.add(6);
a.addAll(b);
operation result:
[1,2,3,4,5,6]
2, List.add: the current list as a list of elements added to it
List a = new ArrayList();
a.add(1);
a.add(2);
a.add(3);
List b = new ArrayList();
b.add(4);
b.add(5);
b.add(6);
a.add(b);
operation result:
[1,2,3, [4,5,6] ]