java - 输入菜单屏幕方法始终返回0

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Is Java “pass-by-reference” or “pass-by-value”?

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去年关闭。





我被分配去创建一个菜单驱动程序，其中包含一个显示菜单屏幕/获取用户输入的功能，但是displaymenu()始终且仅返回0而不是新输入的数字。

我对编程还很陌生，并且已经搜索了所有我能想到的东西，而且我很困。

import java.util.Scanner;

public class menuDriven
{
   public static void main(String[] args)
   {
      int menuSelection=0;
      double inches, centimeters, feet, meters, miles, kilometers;

      Scanner keyboard = new Scanner(System.in);

      displayMenu(keyboard, menuSelection);


      switch(menuSelection)
      {
      case 1:
         inchesToCentimeters(keyboard);
         break;

      case 2:
         feetToMeters(keyboard);
         break;

      case 3:
         milesToKilometers(keyboard);
         break;
      }

   } // end main

   public static int displayMenu(Scanner keyboard,  int menuSelection)
   {

   System.out.println("1. Convert inches to centimeters");
   System.out.println("2. Convert feet to meters");
   System.out.println("3. Convert miles to kilometers");
   System.out.println();

   System.out.println("Enter your selection");
   menuSelection = keyboard.nextInt();
    while (menuSelection < 1 || menuSelection > 3)
      {
         System.out.println("Please enter 1, 2, or 3.");
         menuSelection = keyboard.nextInt();
      }
   return menuSelection;
   }

   public static void inchesToCentimeters(Scanner keyboard)
   {
      double inches, centimeters;
      System.out.print("Enter the number of inches: ");
      inches = keyboard.nextDouble();
      centimeters = inches * 2.54;
      System.out.println("That is equal to " + centimeters + "
centimeters.");

   }

   public static void feetToMeters(Scanner keyboard)
   {
      double feet, meters;
      System.out.println("Enter the number of feet: ");
      feet = keyboard.nextDouble();
      meters = feet * 0.3048;
      System.out.println("That is equal to " + meters + " meters.");
   }

   public static void milesToKilometers(Scanner keyboard)
   {
      double miles, kilometers;
      System.out.println("Enter the number of miles: ");
      miles = keyboard.nextDouble();
      kilometers = miles * 1.609;
      System.out.println("That is equal to " + kilometers + "
kilometers.");
   }
} // end class

程序应使用用户输入1、2或3，然后将该数字输入开关并显示代码。

最佳答案

Java通过值传递原始参数，因此，尽管您在menuSelection中操纵displayMenu参数，但menuSelection中的main与调用displayMenu之前的一样。

您可以将displayMenu的结果分配给menuSelection：

menuSelection = displayMenu(keyboard, menuSelection);

您还可以删除作为参数的menuSelection传递并将其在displayMenu内声明，例如：

public static int displayMenu(Scanner keyboard) {
    int menuSelection=0;

    //...
}