java - 带方法的 Palindrome.java

Question

该程序运行时不会引发任何异常，但无论输入如何，结果始终相同:““空白”是回文。”每次输入都是回文时，我只是想知道是否有人对为什么会发生这种情况有任何建议？下面是该程序的代码:

class Palindrome
{
    public static void main(String args[])
    {
        int num = 0;
        int dig1 = 0;
        int dig2 = 0;
        int dig3 = 0;
        int dig4 = 0;
        int dig5 = 0;
        boolean digits = true;

        retrieveInput(num);
        check(num,dig1,dig2,dig3,dig4,dig5);
        display(digits,num);
    }

    public static int retrieveInput(int num)
    {
        String number;
        number = JOptionPane.showInputDialog("Enter A Five Digit Number.");
        num = Integer.parseInt(number);

        while(num < 9999 || num > 99999)
        {
            JOptionPane.showMessageDialog(null, num + " Is Not A Five Digit Number",
                "ERROR", JOptionPane.ERROR_MESSAGE);        
            number = JOptionPane.showInputDialog("Enter A Five Digit Number.");
            num = Integer.parseInt(number);

        }
        return num;
    }

    public static boolean check(int num,int dig1,int dig2,int dig3,int dig4,int dig5)
    {
        boolean digits;

        dig1 = num / 10000;
        dig2 = num % 10000 / 1000;
        dig3 = num % 10000 % 1000 / 100;
        dig4 = num % 10000 % 1000 % 100 /10;
        dig5 = num % 10000 % 1000 % 100 % 10 / 1;

        if (dig1 == dig5 && dig2 == dig4)
            digits = true;
        else
            digits = false;

        return digits;
    }

    public static void display(boolean digits, int num)
    {
        num = retrieveInput(num);
        if (digits = false)
            JOptionPane.showMessageDialog(null, num + " is a palindrome");
        else
            JOptionPane.showMessageDialog(null, num + " is not a palindrome");
    }
}

Answer 1

在display(boolean, int)的第二行，您正在尝试将 boolean 值与 = 进行比较运算符(operator)。这设置 digits至false我想你的意思是:

        if (digits == false)

if 语句需要一个 boolean 值作为输入，即 if(bool) 。您不需要像if(bool == true)那样检查这是真还是假。因为bool == true始终评估为等于 bool 。说bool == true是完全多余的。然而，你bool == false始终计算为 bool 的相反值。 !运算符翻转以下 boolean 值的值，例如!true计算结果为 false 。 !bool因此总是评估 bool 的相反值，与 bool == false 相同.

因此，您只需要:

        if (!digits)

这样做也被认为是良好的做法。

使代码更短的另一种方法是使用三元运算符。这不一定是最好的做法，但我个人喜欢这样做:

替换

if (digits = false)
    JOptionPane.showMessageDialog(null, num + " is a palindrome");
else
    JOptionPane.showMessageDialog(null, num + " is not a palindrome");

与

JOptionPane.showMessageDialog(null, num + " is " + (digits ? "not " : "") + "a palindrome");

有关三元运算符的更多信息，请参阅以下页面:

• How does the ternary operator work?
• How do I use the conditional operator?
• http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op2.html

另一件事需要注意的是，您不需要将输入处理为整数，因为您从不在算术语句中使用数字；您只需将数字的数字相互比较即可。在此工作代码中，我将其作为字符串处理，因此它要短得多:

import javax.swing.*;

class Palindrome
{
    public static void main(String args[])
    {
        display();
    }

    /**
     * Returns a five-digit string
     */
    public static String retrieveInput()
    {
        String number = JOptionPane.showInputDialog("Enter A Five Digit Number:"); //get input
        while(number.length() != 5) //continue to get input while it is not five digits
        {
            JOptionPane.showMessageDialog(null, number + " Is Not A Five Digit Number",
                "ERROR", JOptionPane.ERROR_MESSAGE);        
            number = JOptionPane.showInputDialog("Enter A Five Digit Number:");
        }
        return number; //return the input
    }

    /**
     * Returns whether the given five digit string is a palindrome
     */
    public static boolean check(String number)
    {
        return (number.charAt(0) == number.charAt(4) && number.charAt(1) == number.charAt(3)); //checks to see if the first character equals the fifth character and the second character equals the fourth character
    }

    public static void display()
    {
        String number = retrieveInput(); //gets input

        if(check(number)) //if it is a palindrome
        {
            JOptionPane.showMessageDialog(null, number + " is a palindrome"); //say it is a palindrome
        }
        else
        {
            JOptionPane.showMessageDialog(null, number + " is not a palindrome"); //say it isn't a palindrome
        }
    }
}