在java实验室中使用While(用户输入无效输入)

Question

我在上课的一部分实验室遇到了一些麻烦,大部分都很容易,但由于某种原因,我的声明并没有按照我的意愿行事.它应该返回无效输入,然后提示用户租用; 但是,它认为每个输入都无效.(应该很容易在代码中看到)我该如何解决这个问题？或者我可以找到这些信息,因为我无法在我的书中找到它.(第二个while循环,第一个工作)

import java.util.ArrayList;
import java.util.Scanner;
import javax.swing.JOptionPane;

public class lab8
{
    public static void main (String[] args)
    {
        int choice;
        String item;
        double costper;
        ArrayList <String> Items = new ArrayList <String> (); 
        Items.add ("computer");
        Items.add ("Monitor");
        Items.add ("Color Printer");
        Items.add ("Color Scanner");
        Items.add ("DVD/CDROM");
        Items.add ("To Quit");

        ArrayList <Integer> Num = new ArrayList <Integer> ();
        Num.add (0);
        Num.add (1);
        Num.add (2);
        Num.add (3);
        Num.add (4);
        Num.add (5);

        System.out.println ("\t\tMy Super Computer Store\n");
        int index=0;
        int endex= 0;
        while (index < Items.size() && endex < Num.size())
        {
            System.out.println ("\t" +Num.get(index)+"\t"+Items.get (endex));
            index++;
            endex++;
        }
        Scanner scan = new Scanner (System.in);
        System.out.print ("\n\t\t\tEnter the item to purchase: ");
        choice = scan.nextInt ();
        {
            if (choice==5)
            {
                JOptionPane.showMessageDialog (null, "Thanks for considering My Super Computer Store");
                System.exit (0);
            }
        }
        {
            if (choice==0 || choice==1 || choice==2 || choice==3 || choice==4)
            {
                item = Items.get (choice);
            }
        }
        while (choice!=0 || choice!=1 || choice!=2 || choice!=3 || choice!=4 || choice!=5)
        {
            System.out.println ("Invalid Input, Please enter a integer between 0 and 5. ");
            System.out.print ("\n\t\t\tEnter the item to purchase: ");
            choice = scan.nextInt ();    
        }
        System.out.print ("\n\n\t\t\tEnter the quantity to purchase: ");
        int Qty = scan.nextInt ();
    }
}

Answer 1

你的逻辑错了.

你要:

!(choice == 0 || choice == 1 || choice == 2 || choice == 3 || choice == 4)

这和你写的不一样.

德摩根定律是你的朋友:)

请注意,根据德莫根定律

!(choice == 0 || choice == 1 || choice == 2 || choice == 3 || choice == 4)

是

(choice != 0 && choice != 1 && choice !=2 && choice !=3 && choice != 4)

当然,既然您使用的是整数,那么您也可以使用以下条件:

(choice < 0 || choice > 4)