Java中的逻辑和循环问题 [英] Issue with logic and Loop in Java

问题描述

我开始用Java编写小程序.我想练习try-catch块，但我什至没有来到那部分而陷入循环部分.我知道这是一个非常基本的循环问题，但我想我陷入了一个非常简单的逻辑问题.我需要从该程序中获得帮助，如果用户按1，则跳转到switch语句并执行适当的大小写.如果用户按下1或2以外的任何键，则返回MenuLoop功能并再次执行它，直到按下正确的数字(1或2)为止.我使用While循环进行控制.这是代码.

I started coding small program in Java. I wanted to exercise try-catch block, but i did not even come to that part and got stuck on loop part. I know this is very basic loop issue, but i guess i caught myself in a very simple logical problem. What I need from this program is if a user press 1, then to jump to switch statement and execute proper case. If a user press anything but 1 or 2, to go back to the MenuLoop function and execute it again until pressed correct number (1 or 2). I used While loop for control. Here is the code.

import java.util.Scanner;

    public class TryCatchExercise {

    public static void MenuLoop() {
    Scanner input = new Scanner(System.in);
    int choice;

    System.out.println("1. Check for Number 1");
    System.out.println("2. Check for Number 2");
    System.out.print("Please enter your choice... ");
    choice = input.nextInt();
    while (choice != 1 || choice != 2) {
        System.out.println("Invalid entry, press 1 or 2");
        MenuLoop();
    }    //Isn't it logical at this point for loop to be skipped and 
         // go to Switch if a user pressed 1 or 2.??

    switch (choice) {
    case 1:
        System.out.println("Pressed 1");
        break;
    case 2:
        System.out.println("Pressed 2");
        break;
    default:
        System.out.println("Invalid number");
    }
}

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

}

}
 OUTPUT
 1. Check for Number 1
 2. Check for Number 2
 Please enter your choice... 1
 Invalid entry, press 1 or 2
 1. Check for Number 1
 2. Check for Number 2
 Please enter your choice... 2
 Invalid entry, press 1 or 2
 1. Check for Number 1
 2. Check for Number 2
 Please enter your choice... 5
 Invalid entry, press 1 or 2
 1. Check for Number 1
 2. Check for Number 2
 Please enter your choice... 

推荐答案

这是一个逻辑问题，"choice"值应为1或2. 在您的(while)语句中，您正在检查选择"是否与1相同 而且选择"与2相同.永远不会达到此条件，因为选择"可以是1或2，但不能同时是两个值.这只是对情况的解释.

This is a logical problem, the "choice" value should be either 1 or 2. In your (while) statement you are checking that "choice" is not different from 1 but also that "choice" is not different from 2. This condition is never reached because "choice" can be either 1 or 2 but not both values at the same time. This is only an explanation of the situation.

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