尝试循环任何不是1-3和/或在其选择过程结束时的用户选择int

Question

我不确定我是否也正确使用了公共静态int。总的来说，我觉得这个代码一团糟，我只是不断地添加越来越多我可能不需要的东西，但这一点我仍然不太清楚如何让它以我想要的方式循环。

import java.util.Scanner;
public class Program7 {
    public static void main(String[] args) {
        // main menu
        mm();
        int choice = 0;
        switch (choice) {
            // addition
            case 1:
                add();  
                break;
            // subtraction
            case 2:
                sub();
                break;
            // exit
            case 3:
                System.out.print("GOOD BYE ^__^");  
                break;
            // if choice >3 or <1
            default:
                System.out.print("nInvalid selection.nPlease select from (1-3): ");
                Scanner kb = new Scanner(System.in);
                choice = kb.nextInt();
        }
   }

添加

public static int add() {
    System.out.print("nEnter number1: ");
    Scanner kb = new Scanner(System.in);
    int num1 = kb.nextInt();
    System.out.print("Enter number2: ");
    int num2 = kb.nextInt();
    int sum = num1 + num2;
    System.out.print("n" + num1 + " + " + num2 + " = " + sum);
    return sum; 
}

相减

public static int sub() {
    System.out.print("Enter number1: ");
    Scanner kb = new Scanner(System.in);
    int num1 = kb.nextInt();
    System.out.print("Enter number2: ");
    int num2 = kb.nextInt();
    int diff = num1 - num2;
    System.out.print(num1 + " - " + num2 + " = " + diff);
    return diff;
}

无效号码（<1或>3）的主菜单和/或用户完成选择后，直到选择号码3:

public static int mm() {
    System.out.print("==MAIN MENU==n1.Additionn2.Subtractionn3.ExitnnSelect Menu(1-3): "); 
    Scanner kb = new Scanner(System.in);
    int choice = kb.nextInt();
    return choice;
}

Answer 1

代码大部分已经完成。要将其放入循环中，请使用while(true):

public static void main(String[] args) {
    while (true) {
        int choice = mm();
        // rest of method

退出时，不要使用退出switch块的break;，而是使用完全退出程序的System.exit(0);。

Answer 2

这样的东西就足够了：

while( true )
{
    // Display menu and let user pick one choice.
    switch( choice )
    {
        // Other cases till here.
        default: exit.
    }
}