Question

我对这个编程的东西基本上是新手。有一部分代码我无法理解，也不知道该怎么做。可能是我们的教练没有讨论的内容。我想要发生的是当我输入“Y”时，它会重试整个程序。如果我输入“N”，它将退出。这是代码

import java.io.*;
import javax.swing.JOptionPane;

public class Doge {

    public static void main(String[] args) 
    {
        int start = 0;
        int end = 0;
        int step = 0;
        String input = "";
        BufferedReader in = new BufferedReader (
                new InputStreamReader (System.in));

        try 
        {
            System.out.println("Input starting number: ");
            input = in.readLine();
            start = Integer.parseInt(input);

            System.out.println("Input ending number: ");
            input = in.readLine();
            end = Integer.parseInt(input);

            System.out.println("Input step number: ");
            input = in.readLine();
            step = Integer.parseInt(input);

        }
        catch (IOException e)
        {
            System.out.println("Error");
        }

        System.out.println("");
        if (start>=end)
        {
            System.out.println("Starting number should be lesser than the ending number.");
        }
        while (start<=end)
        {
            System.out.println(start);
            start = start+step;
        }

        String result = "";
        char y = 'Y';
        char n = 'N';

        BufferedReader it = new BufferedReader (
                new InputStreamReader(System.in));
        try 
        {
            System.out.print("Do you want to retry (Y/N)? ");
            result = it.readLine();
        }
        catch(IOException e)
        {
            System.out.println("Error");
        }
        start = 0;
        end = 0;
        step = 0;
        input = "";
        BufferedReader in2 = new BufferedReader (
                new InputStreamReader (System.in));
        while ("y".equals(result))
        {
            try 
            {
                System.out.println("Input starting number: ");
                input = in2.readLine();
                start = Integer.parseInt(input);

                System.out.println("Input ending number: ");
                input = in2.readLine();
                end = Integer.parseInt(input);

                System.out.println("Input step number: ");
                input = in2.readLine();
                step = Integer.parseInt(input);
            }
            catch (IOException e)
            {
                System.out.println("Error");
            }

            System.out.println("");

            while (start<=end)
            {
                System.out.println(start);
                start = start+step;
            }
        }

        if ("n".equals(result))
            System.exit(0);
    }
}

我很困惑。我在考虑编写相同的代码，但输入起始编号行后，为步骤编号设置了一个值。

Answer 1

了解Java中的do..while循环.... here

我在您的代码中发现的问题

BufferedReader 不重用
您的重试结果仅检查一次，但不是每次完成一个流程循环
字符串与“y”比较，但不是您定义的char y = 'Y';。 char y = 'Y';应为String y = "Y";（与.equals()的比较区分大小写。因此，如果您想在考虑中加入'y'，则可以使用.equalsIgnoreCase()
{和}不能很好地配合显示相同范围内的语句（易于阅读）

我重写了你的代码，希望可以帮助你理解更多

import java.io.*;
import javax.swing.JOptionPane;

public class Doge {

    public static void main(String[] args) 
    {
        int start = 0;
        int end = 0;
        int step = 0;
        String input = "";
        String result = "";
        boolean invalidInput = false;
        //String y = "Y";
        //String n = "N";

        //reuse same BufferedReader
        BufferedReader in2 = new BufferedReader (
                new InputStreamReader (System.in));

        //use do while to have statement run once then only check retry 
        do
        {
            try 
            {
                do
                {
                    System.out.println("Input starting number: ");
                    input = in2.readLine();
                    start = Integer.parseInt(input);

                    System.out.println("Input ending number: ");
                    input = in2.readLine();
                    end = Integer.parseInt(input);

                    if (start >= end)
                    {
                        System.out.println("Starting number should be lesser than the ending number.");
                        invalidInput = true;
                    }
                    else
                        invalidInput = false;
                } while (invalidInput);  //loop as long as the start >= end

                System.out.println("Input step number: ");
                input = in2.readLine();
                step = Integer.parseInt(input);
            }
            catch (IOException e)
            {
                System.out.println("Error");
            }

            System.out.println("");

            while (start<=end)
            {
                System.out.println(start);
                start = start+step;
            }

            try 
            {
                System.out.print("Do you want to retry (Y/N)? ");
                result = in2.readLine();
                //it will exit if answer is "N" or "n"
                //check whether result is String n (ignore case)
                //if (n.equalsIgnoreCase(result))
                //only accept "n"
                if ("n".equals(result))
                    System.exit(0);
            }
            catch(IOException e)
            {
                System.out.println("Error");
            }
        //} while (y.equalsIgnoreCase(result)); //loop if "y" or "Y"
        } while ("y".equals(result));

        //if here have other process, then your result that is neither 'Y' nor 'N' will run here    
    }
}

运行后，我只知道.equals()和.equalsIgnoreCase()只能用于String而不能用char

关于循环的Java帮助

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