List、Integer[]、int[] 转换

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int数组降序排序

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

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

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

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

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

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

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

 

 

int数组降序排序

    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();