Java中高效提取字符串中指定长度单词的教程

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

public class WordExtractor {

    /**
     * 从给定的字符串中提取所有指定长度的单词。
     *
     * @param sentence    输入的句子，单词之间以空格分隔。
     * @param wordLength  目标单词的长度。
     * @return 包含所有指定长度单词的字符串数组。
     */
    public String[] findWords(String sentence, int wordLength) {
        // 1. 使用split(" ")将句子分割成单词数组
        //    例如："Monday is a new day" -> {"Monday", "is", "a", "new", "day"}
        String[] words = sentence.split(" ");

        // 2. 将单词数组转换为Stream流
        // 3. 使用filter操作筛选出长度与wordLength相等的单词
        // 4. 使用toArray(String[]::new)将过滤后的单词收集回一个新的String数组
        return Arrays.stream(words)
                     .filter(word -> word.length() == wordLength)
                     .toArray(String[]::new);
    }

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

        String s1 = "Monday is a new day";
        int n1 = 3; // 3字母单词
        String[] result1 = extractor.findWords(s1, n1);
        System.out.println("Input: "" + s1 + "", Length: " + n1 + " -> Result: " + Arrays.toString(result1)); // 预期: {"new", "day"}

        String s2 = "Monday is a new day";
        int n2 = 2; // 2字母单词
        String[] result2 = extractor.findWords(s2, n2);
        System.out.println("Input: "" + s2 + "", Length: " + n2 + " -> Result: " + Arrays.toString(result2)); // 预期: {"is"}

        String s3 = "hello world java programming";
        int n3 = 5; // 5字母单词
        String[] result3 = extractor.findWords(s3, n3);
        System.out.println("Input: "" + s3 + "", Length: " + n3 + " -> Result: " + Arrays.toString(result3)); // 预期: {"hello", "world", "java"}

        String s4 = "a quick brown fox jumps over the lazy dog";
        int n4 = 4; // 4字母单词
        String[] result4 = extractor.findWords(s4, n4);
        System.out.println("Input: "" + s4 + "", Length: " + n4 + " -> Result: " + Arrays.toString(result4)); // 预期: {"quick", "over", "lazy"}

        String s5 = ""; // 空字符串
        int n5 = 3;
        String[] result5 = extractor.findWords(s5, n5);
        System.out.println("Input: "" + s5 + "", Length: " + n5 + " -> Result: " + Arrays.toString(result5)); // 预期: {}

        String s6 = "   leading and trailing spaces   "; // 包含前后空格
        int n6 = 7;
        String[] result6 = extractor.findWords(s6, n6);
        System.out.println("Input: "" + s6 + "", Length: " + n6 + " -> Result: " + Arrays.toString(result6)); // 预期: {"leading", "trailing", "spaces"}
    }
}