如果默认的话如何循环这个switch语句？

Question

我在课堂作业中做了一个 switch 语句，它将根据用户的输入计算矩形的面积或周长，我想这样做，以便如果用户输入无效的输入，程序将循环回到首先要求用户输入“A”或“P”进行相应的计算。

import java.util.Scanner;

public class Switch_Statement_Practice {

    //Create a program that calculates the area or perimeter of a rectangle based on user input.
    
    public static void main(String[] args) {
        Scanner scnr = new Scanner(System.in);
        int height;
        int width;
        char choice;
        
        System.out.println("Do you want to calculate the area or perimeter of the rectangle? Type 'A' for area or 'P' for perimeter.");
        choice = scnr.next().charAt(0); //.charAt(0) returns the character at the specified index position in a string. 0 returns the first characater in a given string.

        switch (choice) {
            case 'A' -> {
                System.out.println("We are going to calculate the area.");
                System.out.println("");
                System.out.println("Enter the height.");
                height = scnr.nextInt();
                System.out.println("Enter the width");
                width = scnr.nextInt();
                System.out.println("The area is " + height * width + " units.");
                break;
            }
            case 'P' -> {
                System.out.println("We are going to calculate the perimeter.");
                System.out.println("");
                System.out.println("Enter the height.");
                height = scnr.nextInt();
                System.out.println("enter the width.");
                width = scnr.nextInt();
                System.out.println("The perimeter is: " + ((2 * height) + (2 * width)));
                break;
            }
            default -> {
                System.out.println("Invalid input. Please enter 'A' or 'P' (Without quotes).");
            }
        }
    }

我尝试声明

boolean invalidInput;

并声明

invalidInput = choice != 'A' && choice != 'P';

，并在要求用户重新输入选择的地方进行

while(invalidInput) {System.out.println("Invalid input. Please enter 'A' or 'P'"); choice = scnr.nextLine().charAt(0);}

循环，但我进入了无限循环。

Answer 1

您可以运行无限循环。如果用户输入有效的输入，那么您可以返回/中断循环。这是代码示例。

导入java.util.Scanner；

公共类 Switch_Statement_Practice {

public static void main(String[] args) {
    Scanner scnr = new Scanner(System.in);
    int height;
    int width;
    char choice;

    while (true) {
        System.out.println("Do you want to calculate the area or perimeter of the rectangle? Type 'A' for area or 'P' for perimeter.");
        choice = scnr.next().charAt(0);

        switch (choice) {
            case 'A' -> {
                System.out.println("We are going to calculate the area.");
                System.out.println("Enter the height:");
                height = scnr.nextInt();
                System.out.println("Enter the width:");
                width = scnr.nextInt();
                System.out.println("The area is " + height * width + " units.");
                return;
            }
            case 'P' -> {
                System.out.println("We are going to calculate the perimeter.");
                System.out.println("Enter the height:");
                height = scnr.nextInt();
                System.out.println("Enter the width:");
                width = scnr.nextInt();
                System.out.println("The perimeter is: " + ((2 * height) + (2 * width)) + " units.");
                return;
            }
            default -> {
                System.out.println("Invalid input. Please enter 'A' or 'P' (Without quotes).");
            }
        }
    }
}

}