我如何做到这一点，以便我的代码不断询问第1、2和3部分以及Choice ：？ 第三次尝试后，扫描仪将关闭

Question

import java.lang.Math;
import java.util.Scanner;

public class Temperature {

    static int fahrenheit;
    static int celsius;

    public static int Celsius(int fahrenheit) {

        fahrenheit = (int) (5.0 / 9.0 * (fahrenheit - 32));
        return fahrenheit;

    }

    public static int Fahrenheit(int fahrenheit) {
        fahrenheit = (int) (9.0 / 5.0 * celsius + 32);
        return fahrenheit;
    }

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner scan = new Scanner(System.in);
        System.out.println("1. Fahrenheit to Celsius");
        System.out.println("2. Celsius to Fahrenheit");
        System.out.println("3. Exit");
        System.out.println("Choice:");

        int choice = scan.nextInt();

        switch (choice) {

        case 1:
            System.out.println("Enter temperature: ");
            fahrenheit = scan.nextInt();
            System.out.println(fahrenheit + " Fahrenheit is " + Celsius(fahrenheit) + " Celsius");
            System.out.println("1. Fahrenheit to Celsius");
            System.out.println("2. Celsius to Fahrenheit");
            System.out.println("3. Exit");
            System.out.println("Choice:");
            choice = scan.nextInt();

        case 2:

            System.out.println("Enter temperature: ");
            celsius = scan.nextInt();
            System.out.println(celsius + " Celsius is " + Fahrenheit(celsius) + " Fahrenheit");
            System.out.println("1. Fahrenheit to Celsius");
            System.out.println("2. Celsius to Fahrenheit");
            System.out.println("3. Exit");
            System.out.println("Choice:");
            choice = scan.nextInt();

        case 3:
            break;

        }

1. Fahrenheit to Celsius
2. Celsius to Fahrenheit
3. Exit Choice: 1 Enter temperature: 100 100 Fahrenheit is 37 Celsius
4. Fahrenheit to Celsius
5. Celsius to Fahrenheit
6. Exit Choice: 2 Enter temperature: 0 0 Celsius is 32 Fahrenheit
7. Fahrenheit to Celsius
8. Celsius to Fahrenheit
9. Exit Choice: 1

After the third attempt, the code doesn't run anymore no matter which choice I input. I want it so it continues to ask as long as the input is either 1 or 2.

Answer 1

Enclose it in a do-while loop

do {
    switch(choice) {
       ...
    }
}while(choice != 3);

Answer 2

You should have a menu method, for example:

public static void showMenu() {
    System.out.println("1. Fahrenheit to Celsius");
    System.out.println("2. Celsius to Fahrenheit");
    System.out.println("3. Exit");
    System.out.println("Choice:");
}

On your main method have a call to this method inside a do-while loop:

public static void main(String args[]) {
    //Add your Scanner code here, your variables, etc
    do {
        showMenu();
        choice = scan.nextInt();

        switch (choice) {
            case 1:
                System.out.println("Enter temperature: ");
                fahrenheit = scan.nextInt();
                System.out.println(fahrenheit + " Fahrenheit is " + Celsius(fahrenheit) + " Celsius");
                break;
            case 2:
                //Do the same for method 1 but for Celsius
    } while (choice != 3);
}

And, you're done!

Answer 3

Just put while-loop or do-while a around your switch-case as likewise,

while(choice!= 3) {
     switch (choice) {
      .....
     }
}

OR

do {
     switch(choice) {
       ......
     }
} while (choice != 3) 

This will lets you to continuously iterate as many time as you want unless you enter 3 .

you can even put the following condition in order to make more secure,

while ( choice >= 3 ) //not recommended but you can.

Answer 4

If you do not want the program to end put it in a while loop:

   Scanner scan = new Scanner(System.in);
   System.out.println("1. Fahrenheit to Celsius");
   System.out.println("2. Celsius to Fahrenheit");
   System.out.println("3. Exit");
   System.out.println("Choice:");

   int choice = scan.nextInt();

   do {
     switch (choice) {
        ...
         }
      } while (choice!= 3);