List 、Integer[]、int[] 轉換

xxx

int數組降序排序

    int[] data = {4,5,6,7,8};

    // int[]轉List<Integer>
    List<Integer> list1 = Arrays.stream(data).boxed().collect(Collectors.toList());

    // int[]轉Integer[]
    Integer[] integers1 = Arrays.stream(data).boxed().toArray(Integer[]::new);

    //List<Integer> 轉int[]
    int[] arr1 = list1.stream().mapToInt(Integer::intValue).toArray();

    //List<Integer> 轉Integer[]
    Integer[] integers2 = list1.toArray(new Integer[0]);

    //Integer[] 轉int[]
    int[] arr2 = Arrays.stream(integers1).mapToInt(Integer::intValue).toArray();

    //Integer[] 轉 List<Integer>
    List<Integer> list2 = Arrays.asList(integers1);

 

 

int數組降序排序

    List<Integer> tmp = Arrays.stream(nums).boxed().collect(Collectors.toList());
    tmp.sort(Comparator.reverseOrder());
    //list.sort(Comparator.comparingInt(Integer::intValue).reversed());
    //personList.sort(Comparator.comparingInt(Person::getAge));
    int[] newNums = tmp.stream().mapToInt(i->i).toArray();

 

低效

            List<Integer> tmp = Arrays.stream(nums).boxed().sorted().collect(Collectors.toList());
            Collections.reverse(tmp);
            int[] newNums = tmp.stream().mapToInt(i->i).toArray();