Java中从字符串提取指定长度单词：Stream API实践指南

String[] words = s.split(" ");
Stream<String> wordStream = Arrays.stream(words);

wordStream.filter(word -> word.length() == wordLength)

.toArray(String[]::new)

import java.util.Arrays;
import java.util.stream.Stream;

public class WordExtractor {

    /**
     * 从给定的句子中提取所有指定长度的单词。
     * 单词通过空格分隔，并只返回长度与wordLength相等的单词。
     *
     * @param s 包含多个单词的输入句子。
     * @param wordLength 要查找的单词的指定长度。
     * @return 包含所有符合指定长度单词的字符串数组。
     */
    public String[] findWords(String s, int wordLength) {
        if (s == null || s.trim().isEmpty()) {
            return new String[0]; // 处理空字符串或只包含空格的字符串
        }

        // 使用split(" ")将句子拆分为单词数组
        // 然后转换为Stream
        return Arrays.stream(s.split(" "))
                     // 过滤掉长度不等于wordLength的单词
                     .filter(word -> word.length() == wordLength)
                     // 过滤掉可能由多个连续空格产生的空字符串
                     .filter(word -> !word.isEmpty()) 
                     // 将过滤后的单词收集回一个String数组
                     .toArray(String[]::new);
    }

    public static void main(String[] args) {
        WordExtractor extractor = new WordExtractor();

        String sentence1 = "Monday is a new day";
        int len1 = 3;
        String[] result1 = extractor.findWords(sentence1, len1);
        System.out.println("Sentence: "" + sentence1 + "", Length: " + len1 + " -> " + Arrays.toString(result1)); // Expected: [new, day]

        String sentence2 = "Monday is a new day";
        int len2 = 2;
        String[] result2 = extractor.findWords(sentence2, len2);
        System.out.println("Sentence: "" + sentence2 + "", Length: " + len2 + " -> " + Arrays.toString(result2)); // Expected: [is]

        String sentence3 = "  hello   world  java ";
        int len3 = 5;
        String[] result3 = extractor.findWords(sentence3, len3);
        System.out.println("Sentence: "" + sentence3 + "", Length: " + len3 + " -> " + Arrays.toString(result3)); // Expected: [hello, world]

        String sentence4 = "";
        int len4 = 3;
        String[] result4 = extractor.findWords(sentence4, len4);
        System.out.println("Sentence: "" + sentence4 + "", Length: " + len4 + " -> " + Arrays.toString(result4)); // Expected: []
    }
}