将Int值转换为整数位数列表

问题描述

我有一个容易的任务来绘制三个int值.然后从绘制的值的最高位数建立一个新的int值.有没有一种简单的方法可以将Int转换为Integer列表?我想通过流来解决此问题，但我需要一个从绘制值创建的整数列表来查找maxValue数字.

I have got an easy task to draw three int values. Then build a new int value from the highest digits from drawn values. Is there an easy way to convert an Int to List of Integers? I want to resolve this by streams but I need a List of Integers created from drawn value to find maxValue digit.

例如:123、256、189 = 369

For example: 123, 256, 189 = 369

我已经以一种幼稚的方式做到了这一点，我仍在学习并开始怀疑这是否是一种更简单，更有效的代码方式.

I have done this in a naive way, I'm still learning and start wondering if is an easier and more code efficient way.

public static List<Integer> convertingValue(int value) {
    List<Integer> intList = new ArrayList<>();
    char[] arr = String.valueOf(value).toCharArray();
    for (int i = 0; i < arr.length; i++) {
        intList.add(Character.getNumericValue(arr[i]));
    }
    return intList;
}

public static void main(String[] args) {
    IntSupplier is = () -> new Random().nextInt(999 - 100 + 1) + 100;
    List<Integer> figuresList =
            List.of(is.getAsInt(), is.getAsInt(), is.getAsInt());

    var list = figuresList
            .stream()
            .map(Basic02::convertingValue)
            .map(x -> x.stream().mapToInt(v -> v)
                    .max().orElseThrow(NoSuchElementException::new))
            .collect(Collectors.toList());

    System.out.println(list);
}

推荐答案

1. 最好使用 Random :: ints(streamSize，origin，bound) 创建随机数流
2. 将每个数字转换为字符串，然后使用 String :: chars 获取每个数字的字符流并找到每个数字的最大数字
3. 为了更好地表示结果，值得在 StringBuilder String 而不是 List< Integer> /code>.然后可以根据需要将此字符串转换为 int/Integer .

1. It would be better to use Random::ints(streamSize, origin, bound) to create a stream of random numbers
2. Convert each number into string, then use String::chars to get stream of characters for each number and find maximal digit for each number
3. To get better representation of the result it is worth to build a String instead of the List<Integer> using custom collector on the basis of StringBuilder. Then this string may be converted then into int/Integer if needed.

String num = new Random().ints(3, 100, 1000)
    .peek(System.out::println) // debug print
    .mapToObj(Integer::toString)
    .map(s -> s.chars().map(Character::getNumericValue).max().getAsInt())
    .collect(Collector.of(StringBuilder::new, StringBuilder::append, StringBuilder::append, StringBuilder::toString));
System.out.println("---\n" + num);

输出:

893
677
436
---
976

---

也可以将现有代码重构为立即返回最大数字而不是整数列表:

---

Existing code may also be refactored to return immediately the maximal digit instead of the list of integers:

public static int getMaxDigit(int value) {
    return String.valueOf(value)
        .chars() // IntStream
        .map(Character::getNumericValue)
        .max() // OptionalInt
        .getAsInt(); // int
}

然后将 List< Integer> 收集为:

var list = new Random().ints(3, 100, 1000) // IntStream
    .map(MyClass::getMaxDigit)
    .boxed()
    .collect(Collectors.toList());

或 String 可以用另一种方式收集:

Or String may be collected in another way:

var str = new Random().ints(3, 100, 1000) // IntStream
    .map(MyClass::getMaxDigit)
    .mapToObj(Integer::toString)
    .collect(Collectors.joining());

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