java - 使用 substring() 和 charAt() 检查字符串是否为回文

Question

我的代码应该要求用户输入一个字符串，然后使用 charAt() 和 substring() 方法检查它是否是回文。我相信，我已经正确完成了所有操作，但 NetBeans 编译不正确。

当我运行代码时，NetBeans 告诉我:

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - missing return statement
    at palindrome.Palindrome.methodA(Palindrome.java:31)
    at palindrome.Palindrome.main(Palindrome.java:27)
Java Result: 1

那么，基本上它说我缺少返回语句？我不明白这怎么可能。

任何帮助将不胜感激。谢谢。

package palindrome;

import java.util.Scanner;

public class Palindrome {

    /**
     * Program asks user to enter a string.
     */
    public static void main(String[] args) {
        String userInput; //user-inputted String
        String result;

        //set up instance of Scanner for user input
        Scanner scan = new Scanner(System.in);

        //ask user for input
        System.out.print("Please enter a String: ");
        userInput = scan.nextLine();

        //run methodA
        result = methodA(userInput);

    }

    public static String methodA(String inString) {
        /*
         * This method checks the user-inputted String against a backward copy
         * of itself using only String and Character methods.
         */

        //next two int variables used as int pointers for first letter of String
        //and last letter of user-inputted String
        int begPoint = 0;
        int endPoint = inString.length() - 1;

        //define Strings to return to main method
        String isPal = (inString + " is a palindrome!");
        String notPal = (inString + " is not a palindrome.");

        while (begPoint < endPoint) {
            //two substrings defined to test String character for character
            String firstChar = inString.substring(begPoint, begPoint + 1);
            String lastChar = inString.substring(endPoint, endPoint + 1);

            //algorithm continues step by step with begPoint going up one and 
            //endPoint decreasing by one
            begPoint++;
            endPoint--;

            //basically here I am trying to check the characters of the user-
            //inputted Strings using the charAt methods but I'm lost when I
            //get to this point
            if (inString.charAt(begPoint) == inString.charAt(endPoint)) {
                return isPal;
            } else {
                return notPal;
            }
        }
    }
}

经过一些回答后——我现在将 while 语句更改为:

while(begPoint<endPoint) {
    //two substrings defined to test String character for character
    String firstChar = inString.substring(begPoint, begPoint + 1);
    String lastChar = inString.substring(endPoint, endPoint + 1);

    //basically here I am trying to check the characters of the user-
    //inputted Strings using the charAt methods 
    if (inString.charAt(begPoint) == inString.charAt(endPoint)) {
        return isPal;
    } else {
        return notPal;
    }

    //algorithm continues step by step with begPoint going up one and 
    //endPoint decreasing by one
    begPoint++;
    endPoint--;
}

但是，现在它告诉我 (begPoint++) 是一个无法访问的语句。

Answer 1

您的问题是您在检查 charAts 之前移动了 begPoint 和 endPoint。将 begPoint 和 endPoint 前移的代码移至使用 charAt 方法之后。