1、数组排序

        Arrays.sort(int[] a)这种形式是对一个数组的所有元素进行排序，并且是按照从小到大的排序。

        

 public static void main(String[] args) {
        Integer []arr = {1,2,3,4,5,6};
        //升序
        Arrays.sort(arr);
        for (int x:arr){
            System.out.print(x + " ");
        }
        System.out.println();
        //升序
        Arrays.sort(arr,new Comparator<Integer>(){
            @Override
            public int compare(Integer o1,Integer o2){
                return o1-o2;
            }
        });
        for(int x:arr){
            System.out.print(x + " ");
        }
        System.out.println();
        //升序
        Arrays.sort(arr, (o1, o2) -> o1 - o2);
        for (int x:arr){
            System.out.print(x + " ");
        }
        System.out.println();
        //降序
        Arrays.sort(arr,new Comparator<Integer>(){
            @Override
            public int compare(Integer o1,Integer o2){
                return o2-o1;
            }
        });
        for(int x:arr){
            System.out.print(x + " ");
        }
        System.out.println();
        //降序
        Arrays.sort(arr, (o1, o2) -> o2 - o1);
        for (int x:arr){
            System.out.print(x + " ");
        }

}

o2 - o1 ---->  降序

o1 - o2 ----> 升序

2、集合排序

        Collections.sort(List<> arr)对一个集合的所有元素进行排序，并且按照从小到大的顺序

 

    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        list.add(4);
        list.add(5);
        list.add(6);
        list.add(3);
        list.add(2);
        list.add(1);
        //升序
        Collections.sort(list);
        for (int x : list){
            System.out.print(x + " ");
        }
        System.out.println();
        //升序
        Collections.sort(list, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1 - o2;
            }
        });
        for (int i = 0; i < list.size(); i++) {
            System.out.print(list.get(i) + " ");
        }
        System.out.println();
        //升序
        Collections.sort(list, (o1,o2) -> o1 - o2 );
        for (int i = 0; i < list.size(); i++) {
            System.out.print(list.get(i) + " ");
        }
        System.out.println();
        //降序
        Collections.sort(list, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2 - o1;
            }
        });
        for (int i = 0; i < list.size(); i++) {
            System.out.print(list.get(i) + " ");
        }
        System.out.println();
        //降序
        Collections.sort(list, (o1,o2) -> o2 - o1 );
        for (int i = 0; i < list.size(); i++) {
            System.out.print(list.get(i) + " ");
        }
    }