Question

如果您输入太多座位，此程序应该会输出错误。如果我输入无效的席位数：经济部门有8个席位。但是如果我输入的数字大于它，则程序不会继续执行else语句并打印错误消息。

相反，它只是通过if语句并使用无效的座位号进行计算。

import java.util.Scanner;

public class FlightProfit
{
        String location;

        int TOLEDO_FARE = 200;
        int HOUSTON_FARE = 300;
        int BOISE_FARE = 400;

        int economySeats;
        int businessSeats;
        int firstClassSeats;

        int economySales;
        int businessSales;
        int firstClassSales;
        //int totalSales = economySales + businessSales + firstClassSales;

        Scanner in = new Scanner(System.in);

        public int addEconomySeats()
        {
            System.out.print("Enter number of economy seats 1-8: ");
            economySeats = in.nextInt();

            if(economySeats > 0 || economySeats < 9)
            {
                return economySeats;
            }
            else
            {
                System.out.println("Error: Only 8 seats available in economy.");
            }
            return 0;
        }

        public int addBusinessSeats()
        {
            System.out.print("Enter number of business seats sold: ");
            businessSeats = in.nextInt();

            if(businessSeats > 0 || economySeats < 7)
            {
                return businessSeats;
            }
            else
            {
                System.out.println("Error: Only 6 seats available in business.");
            }
            return 0;
        }

        public int addFirstClassSeats()
        {
            System.out.print("Enter number of first class seats sold: ");
            firstClassSeats = in.nextInt();

            if(firstClassSeats > 0 || firstClassSeats < 5)
            {
                return firstClassSeats;
            }
            else
            {
                System.out.println("Error: Only 4 seats available in first class.");
            }

            return 0;
        }



       public void getProfit(String loc)
       {
           location = loc;

           if(location.equalsIgnoreCase("toledo"))
           {
               economySales = economySeats * TOLEDO_FARE;
               businessSales = businessSeats * (2 * TOLEDO_FARE);
               firstClassSales = firstClassSeats * (4 * TOLEDO_FARE);
               System.out.println("Economy Sales: " + economySeats + " seats: " + economySales);
               System.out.println("Business Sales: " + businessSeats + " seats: " + businessSales);
               System.out.println("First Class Sales: " + firstClassSeats + " seats: " + firstClassSales);
               //System.out.println("Total Sales: " + totalSales);
           }
           else if(location.equalsIgnoreCase("houston"))
           {
               economySales = economySeats * HOUSTON_FARE;
               businessSales = businessSeats * (2 * HOUSTON_FARE);
               firstClassSales = firstClassSeats * (4 * HOUSTON_FARE);
               System.out.println("Economy Sales: " + economySeats + " seats: " + economySales);
               System.out.println("Business Sales: " + businessSeats + " seats: " + businessSales);
               System.out.println("First Class Sales: " + firstClassSeats + " seats: " + firstClassSales);
              // System.out.println("Total Sales: " + totalSales);
           }
           else
           {
               economySales = economySeats * BOISE_FARE;
               businessSales = businessSeats * (2 * BOISE_FARE);
               firstClassSales = firstClassSeats * (4 * BOISE_FARE);
               System.out.println("Economy Sales: " + economySeats + " seats: " + economySales);
               System.out.println("Business Sales: " + businessSeats + " seats: " + businessSales);
               System.out.println("First Class Sales: " + firstClassSeats + " seats: " + firstClassSales);
               //System.out.println("Total Sales: " + totalSales);
           }
       }
}

== MAIN ==

import java.util.Scanner;

public class Aviation 
{

    public Aviation()
    {

    }

    public static void main(String[] args) 
    {
       int option;

       FlightCost newFlight = new FlightCost();
       FlightProfit flight = new FlightProfit();

       Scanner in = new Scanner(System.in);
       System.out.print("Enter new flight location: ");
       String location = in.next();

       do{
       String menu = "\n Please select an option to perform"
                   + "\n1 (1) Get flight costs."
                   + "\n2 (2) Get flight profits."
                   + "\n3 (3) Enter names/meals."
                   + "\n4 (4) Exit.";

       System.out.println(menu);
       option = in.nextInt();

       }while (option < 0 || option > 4);

       switch(option)
       {
           case 1:
              newFlight.getCost(location);
              break;
           case 2:
              flight.addEconomySeats();
              flight.addBusinessSeats();
              flight.addFirstClassSeats();
              flight.getProfit(location);
              break;
           case 3:
               //newFlight.flyers();
               break;
           case 4:
               System.out.println("Exit");
               break;
           default:
               System.out.println("Error: must select menu option.");
       }      
    }   
}

Answer 1

if (economySeats > 0 || economySeats < 9)

这种情况总是正确的（因为任何数字都是正数或小于9），所以当然你没有达到else子句。

您可能需要&&（和）运算符：

if (economySeats > 0 && economySeats < 9)

您的其他条件也有同样的错误。

Answer 2

if (economySeats > 0 && economySeats < 9)

因为economySeats应该大于0且小于9.然后只有条件将跟随else语句。

使用if (economySeats > 0 || economySeats < 9)时这意味着economySeat应该大于0（所以如果你输入大于0的值那么这个条件就是真的）所以，这就是你认为if语句不起作用的原因。

Answer 3

您的号码范围检查无法按照您的意图运行的原因已经给出。我喜欢暗示你可以通过使用Guava＆＃39; Range＆＃39;类型：

Range economySeatsRange = Range.atLeast(1).atMost(8);
//...
boolean inAllowedRange = economySeatsRange.apply(economySeats);
if(inAllowedRange)
    // between 1 and 8
else
    // signal error

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Range.html

程序不会去其他声明

3 个答案: