如何确定用户的输入字符串是否向后读取（回文）JAVA [关闭]

Question

package com.jetbrains;

import java.util.Objects;
import java.util.Scanner;

public class SA {

    public static void main(String[] args) {

        //scanner object
        Scanner input = new Scanner(System.in);

        //comment 
        System.out.println("Please enter a line of text below:");
        String letters = input.nextLine(); //User's string input

        if (letters.length() < 7) {
            System.out.println("The input is too short.");
        }

        //variables
        int l = letters.length()-5; //where the last 5 characters are located in user's input string
        String answer = letters.substring(l) + letters.substring(2,l) + letters.substring(0, 2); // first 2 & last 5 swapped


        if (letters.length() > 7) {
            System.out.println("Convert to upper cases:"); 
            System.out.println(letters.toUpperCase());

            System.out.println("Swap the first 2 characters with the last 5 characters:"); // Swap
            System.out.println(answer);

            System.out.println("Is it a palindrome?");

            for (int i = (letters.length() - 1); i >= 0; i--) {
                char backwards = (letters.charAt(i));

                for (int n = letters.indexOf(0); n >= 0; n++) {
                    char forwards = (letters.charAt(n));

                    if (Objects.equals(forwards, backwards)) {
                        System.out.println("True");
                        else
                           System.out.println("False");
                    }


                }
            }
        }

    }
}

我尝试通过将 for 循环输出转换为 char 变量来比较用户的输入，但它总是返回 false。我不确定如何解决最后一点，我尝试过做其他事情，但我完全被难住了。我的班级没有学习过 StringBuilder 或 StringBuffer，所以我不能在我的代码中使用它们。任何提示或提示都会非常有帮助，谢谢。

Answer 1

我已经稍微修改了你的代码以获得正确的结果 -

import java.util.Scanner;

public class StringAnalysis {

    public static void main(String[] args) {

        //Create scanner object
        Scanner input = new Scanner(System.in);

        //Comment to the user
        System.out.println("Please enter a line of text below:");
        String letters = input.nextLine(); //User's string input

        if (letters.length() < 7) {
            System.out.println("The input is too short. No analysis to be performed.");
        }

        //variables
        int l = letters.length() - 5; //States the index number of where the last 5 characters are located in user's input string
        String answer = letters.substring(l) + letters.substring(2, l) + letters.substring(0, 2); // first 2 & last 5 swapped


        if (letters.length() > 7) {
            System.out.println("Analysis #1: Convert to upper cases:"); // Upper case
            System.out.println(letters.toUpperCase());

            System.out.println("Analysis #2: Swap the first 2 characters with the last 5 characters:"); // Swapping
            System.out.println(answer);

            System.out.println("Analysis #3: Is it a palindrome?");


            String backwards = "";
            for (int i = (letters.length() - 1); i >= 0; i--) {
                backwards = backwards + letters.charAt(i);
            }

            if(letters.equalsIgnoreCase(backwards)) {
                System.out.println("True");
            } else {
                System.out.println("False");
            }
        }
    }
}

Answer 2

您在检查回文的第二个循环中遇到问题，我试图解决它，但尽管它会将每个向后的字母与所有向前的字母进行比较，这在逻辑上是错误的，您可以做一些更好的事情：

System.out.println("Analysis #3: Is it a palindrome?");
        boolean response = true;
        for (int i = 0 ; i < letters.length() ; i++) {
            String backwards = String.valueOf(letters.charAt(i));
            String forwards = String.valueOf(letters.charAt(letters.length()-i-1));

                if(!backwards.equals(forwards)) {
                    response = false;
                }

        }
        System.out.println(response);