java - 如何让我的程序在收到指示之前不关闭[距离转换]

Question

我似乎不知道在 while 循环中输入什么或输入什么内容。一切正常，但是当我输入转换后，如何让它询问我是否要输入另一个问题。

import java.util.Scanner; 

public class DistanceConversion 
{ 
    public static void showKilometers(double meters)
    {
        double kilometers = meters * 0.001; 
        System.out.println(meters +" meters is " + kilometers + " kilometers."); 
    } 

    public static void showInches(double meters) 
    { 
        double inches = meters * 39.37; 
        System.out.println(meters +" meters is " + inches + " inches."); 
    } 

    public static void showFeet(double meters) 
    { 
        double feet = meters * 3.281; 
        System.out.println(meters +" meters is " + feet + " feet."); 
    } 

    public static void quitProgram() 
    { 
        System.out.println("Goodbye!"); 
        System.out.println(0); 
    } 
    public static void showMenu() 
    { 
        System.out.println(" 1. Convert to kilometers "); 
        System.out.println(" 2. Convert to inches "); 
        System.out.println(" 3. Convert to feet "); 
        System.out.println(" 4. Quit the program "); 
        System.out.println(" "); 
    } 

    public static void main (String [] args) 
    { 
        double meters; 
        int choice; 
        Scanner scan = new Scanner (System.in); 

        System.out.print("Enter a distance in meters: "); 
        meters = scan.nextDouble(); 
        showMenu(); 
        choice = scan.nextInt(); 

        switch(choice) 
        { 
            case 1:showKilometers(meters); 
            break; 
            case 2:showInches(meters); 
            break; 
            case 3:showFeet(meters); 
            break; 
            case 4:quitProgram(); 
        }
    }
}

Answer 1

你想重复什么？整个计划？然后附上“整个程序”又名。主逻辑带有 while 循环，检查输入是否等于 4 或其他任意退出 int。

在顶部声明“int choice”，然后将其余部分括起来。

while(choice >= 1 && choice <=3)
{
   //main-method code here
}

编辑(为了清晰起见):

int choice = 0; 
while(choice != 4)
{
        double meters; 
        Scanner scan = new Scanner (System.in); 

        System.out.print("Enter a distance in meters: "); 
        meters = scan.nextDouble(); 
        showMenu(); 
        choice = scan.nextInt(); 

        switch(choice) 
        { 
            case 1:showKilometers(meters); 
            break; 
            case 2:showInches(meters); 
            break; 
            case 3:showFeet(meters); 
            break; 
            case 4:quitProgram(); 
        }
}