Question

我正在尝试输入一个四字的句子，然后能够使用indexOf和substrings分别打印出每个单词。我有什么想法我做错了吗？

被修改

它应该是什么样子？我已经运行了两次并收到两个不同的答案，所以我不确定运行该程序的程序是否有问题或程序本身是否有问题。

import java.util.Scanner;
public class arithmetic {
public static void main(String[] args) {
    Scanner in = new Scanner(System.in);

    String sentence;
    String word1, word2, word3, word4;
    int w1, w2, w3, w4;
    int p, p2, p3, p4;

    System.out.print("Enter a sentence with 4 words: ");
    sentence = in.nextLine();

    p = sentence.indexOf(" ");



    word1 = sentence.substring(0,p)+" ";
    w1 = 1 + word1.length();
    p2 = word1.indexOf(" ");
    word2 = sentence.substring(w1,p2);
    w2 = w1+1+word2.length();
    p3 = word2.indexOf(" ");
    word3 = sentence.substring(w2,p3);
    w3 = w1+w2+1+word3.length();
    p4 = word3.indexOf(" ");
    word4 = sentence.substring(w3,p4);
    w4 = w1+w2+w3+1+word4.length();

Answer 1

我至少看到两件事：

您没有正确计算指数。第三个单词的起始索引应该类似于length of first word + 1 + length of second word + 1，但看起来你要忽略第一个单词的长度。同样地，当你得到第四个单词时，你会忽略前两个单词的长度。
indexOf(" ")只会获取第一次出现空格的索引。获得第一个空格后，您将重用该索引，而不是使用其他空格的索引。

最后，在你修复这两个之后，如果你知道这些单词将被空格分隔，那么你可能想要查看String.split函数。使用它，您可以分割您的句子而无需自己进行所有空间查找。

Answer 2

由于性能原因，可读性和错误，我几乎不建议不使用substring和indexOf。考虑以下任何一个（所有这些都将单词视为非空白字符）：

public static void main (String[] args) throws java.lang.Exception
{
    int wordNo = 0;

    System.out.println("using a Scanner (exactly 4 words):");

    InputStream in0 = new ByteArrayInputStream("a four word sentence".getBytes("UTF-8"));
    Scanner scanner = new Scanner(/*System.*/in0);

    try {
        String word1 = scanner.next();
        String word2 = scanner.next();
        String word3 = scanner.next();
        String word4 = scanner.next();
        System.out.printf("1: %s, 2: %s, 3: %s, 4: %s\n", word1, word2, word3, word4);
    } catch(NoSuchElementException ex) {
        System.err.println("The sentence is shorter than 4 words");
    }

    System.out.println("\nusing a Scanner (general):");

    InputStream in1 = new ByteArrayInputStream("this is a sentence".getBytes("UTF-8"));

    for(Scanner scanner1 = new Scanner(/*System.*/in1); scanner1.hasNext(); ) {
        String word = scanner1.next();
        System.out.printf("%d: %s\n", ++wordNo, word);
    }


    System.out.println("\nUsing BufferedReader and split:");

    InputStream in2 = new ByteArrayInputStream("this is another sentence".getBytes("UTF-8"));

    BufferedReader reader = new BufferedReader(new InputStreamReader(/*System.*/in2));
    String line = null;
    while((line = reader.readLine()) != null) {
        for(String word : line.split("\\s+")) {
            System.out.printf("%d: %s\n", ++wordNo, word);
        }
    }
}

如何从字符串中提取子串（单词）？

2 个答案: