java.util.Collections

 

java.util包下的Collections类，该类主要用于操作集合或者返回集合

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

List<Integer> list = new ArrayList<>(); list.add(2); list.add(1); list.add(3);   Collections.sort(list);//升序 System.out.println(list); Collections.reverse(list);//降序 System.out.println(list);   Integer max = Collections.max(list);//获取最大值 Integer min = Collections.min(list);//获取最小值 System.out.println(max); System.out.println(min);   List<Integer> integers = Collections.synchronizedList(list);//将ArrayList转换成线程安全集合 System.out.println(integers);   List<Object> emptyList = Collections.emptyList();//返回空集合 System.out.println(emptyList);   int i = Collections.binarySearch(list, 3);//二分查找 System.out.println(i);   List<Integer> integers2 = Collections.unmodifiableList(list);//转换成不可修改集合 integers2.add(4); System.out.println(integers2);