java list 函数

List<String> a = new ArrayList<String>();
List<String> b = new ArrayList<String>();
System.out.prinln(a)
// []
System.out.prinln(b)
// [] 

a.add("A");
a.add("B");
System.out.println(a)
// [A,B]

b.add("B");
b.add("C");
System.out.println(a)
// [C,D]

List<String> c = a;
List<String> d = b;

c.remove("B");
System.out.println(c)
// [C]

c.removeAll(b)
System.out.println(a)
// [A] 

a.retainAll(b);
System.out.println(a)
// [B]

List<String> list = new ArrayList<String>();
Object[] array = list.toArray();

List<String> list = new ArrayList<String>(array.length);
Collections.addAll(list, array);