java - 如何忽略 java 中的标点符号和空格？

Question

import java.util.Scanner;
public class Ex3 {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Please input a word: ");
        String Line = keyboard.nextLine();
        boolean x = isReverse(Line);
        System.out.print("It is " + x + " that this word is a palindrome.");
    }
    public static boolean isReverse(String Line) {
        int length = Line.length();
        boolean x = true;
        String s = "";
        for (int i = 0; i < length; i++) {
            if (Line.charAt(i) != ' ') {
                s += Line.charAt(i);
            }
        }
        for (int i = 0; i < length; i++) {
            if (Line.charAt(i) != Line.charAt(length - 1 -i)) {
                x = false;
            }
        }
        return x;   
    }
}

我想做的是编写一个程序，将单词或短语作为输入并根据它是否为回文返回 true 或 false。在程序中，我应该忽略空格和标点符号，并制作回文，例如“A man, a plan, a canal, Panama”。我想我已经解决了空白问题，但不知道如何忽略所有标点符号。

Answer 1

你可以使用 a regular expression从字符串中删除所有非单词字符:\\W 代表非单词字符

String s = "A man, a plan, a canal, Panama.";
String lettersOnly = s.replaceAll("[\\W]", "");
System.out.println("lettersOnly = " + lettersOnly);

输出:

lettersOnly = AmanaplanacanalPanama

如果你想减少你的代码长度，你也可以使用StringBuilder#reverse反转字符串:

public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);
    System.out.print("Please input a word: ");
    String line = keyboard.nextLine();

    String cleanLine = line.replaceAll("[\\W]", "");
    String reverse = new StringBuilder(cleanLine).reverse().toString();
    boolean isPalindrome = cleanLine.equals(reverse);

    System.out.print("It is " + isPalindrome + " that this word is a palindrome.");
}

编辑

如果你需要坚持循环，如果字符是字母，你可以简单地检查你的循环:

public static boolean isReverse(String Line) {
    int length = Line.length();
    boolean x = true;
    String s = "";
    for (int i = 0; i < length; i++) {
        if ((Line.charAt(i) >= 'a' && Line.charAt(i) <= 'z')
          || (Line.charAt(i) >= 'A' && Line.charAt(i) <= 'Z')) {
            s += Line.charAt(i);
        }
    }

注意:您将遇到大小写问题 (A != a) - 一个简单的解决方法是首先使用 将所有字符设为小写String lowerCase = Line.toLowerCase();.