java - 如何修复我的 "java.util.InputMismatchException"错误？

Question

我需要做的就是再次循环，以便用户可以继续使用该程序。让我知道是否有任何我可以阅读的引用资料，以帮助我更多地了解这个问题。提前致谢。

import java.util.Scanner;

public class Module3Assignment1 {

    // public variables
    public static String letterChosen;
    public static int loop = 0;
    public static double radius, area;
    public static Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) {

        // tells user what the program is about
        System.out.println("Welcome to the Round Object Calculator");
        System.out.println("This program will calculate the area of a circle of the colume of a sphere.");
        System.out.println("The calculations will be based on the user input radius.");
        System.out.println("");

            // loops while the user wants to calculate information
            while (loop == 0){

                Input();
                System.out.print(Answer());

                System.out.println("Do you want to calculate another round object (Y/N)? ");
                String input = scanner.next().toUpperCase();
                    if (input == "N"){
                        loop = 1;
                        }
            }

        // ending message/goodbye
        Goodbye();
        scanner.close();

    }

    private static void Input(){

        // prompts user for input
        System.out.print("Enter C for circle or S for sphere: ");
        letterChosen = scanner.nextLine().toUpperCase();
        System.out.print("Thank you. What is the radius of the circle (in inches): ");
        radius = scanner.nextDouble();

    }

    private static double AreaCircle(){

        // calculates the area of a circle
        area = Math.PI * Math.pow(radius, 2);
        return area;

    }

    private static double AreaSphere(){

        // calculates the area of a sphere
        area = (4/3) * (Math.PI * Math.pow(radius, 3));
        return area;

    }

    private static String Answer(){

        //local variables
        String answer;

        if(letterChosen == "C"){
            // builds a string with the circle answer and sends it back
            answer = String.format("%s %f %s %.3f %s %n", "The volume of a circle with a radius of", radius, "inches is:", AreaCircle(), "inches");
            return answer;
        }else{
            // builds a string with the sphere answer and sends it back
            answer = String.format("%s %f %s %.3f %s %n", "The volume of a sphere with a radius of", radius, "inches is:", AreaSphere(), "cubic inches");
            return answer;
        }
    }

    private static String Goodbye(){

        // local variables
        String goodbye;

        // says and returns the goodbye message
        goodbye = String.format("%s", "Thank you for using the Round Object Calculator. Goodbye");
        return goodbye;
    }

}

以下是控制台输出和执行后出现的错误

Welcome to the Round Object Calculator
This program will calculate the area of a circle of the colume of a sphere.
The calculations will be based on the user input radius.

Enter C for circle or S for sphere: C
Thank you. What is the radius of the circle (in inches): 12
The volume of a sphere with a radius of 12.000000 inches is: 5428.672 cubic inches 
Do you want to calculate another round object (Y/N)? 
Y
Enter C for circle or S for sphere: Thank you. What is the radius of the circle (in inches): C
Exception in thread "main" java.util.InputMismatchException
    at java.util.Scanner.throwFor(Scanner.java:840)
    at java.util.Scanner.next(Scanner.java:1461)
    at java.util.Scanner.nextDouble(Scanner.java:2387)
    at Module3Assignment1.Input(Module3Assignment1.java:48)
    at Module3Assignment1.main(Module3Assignment1.java:24)

Answer 1

import java.util.Scanner;

public class Module3Assignment1 {
// public static variables are discouraged... 
private static char letterChosen; //char takes less memory 
private static char useAgain = 'Y'; //just use the answer to loop... 
private static double radius, area;
private static String answer;
private  static Scanner scanner = new Scanner(System.in);


//you might want to clear the screen after the user gave an answer to another round object
private static void clearScreen(){
    for(int i =0;i<50;i++){System.out.print("\n");}
}

public void input(){

    // prompts user for input
    System.out.print("Enter C for circle or S for sphere: ");
    letterChosen = scanner.next().charAt(0);
    System.out.print("Thank you. What is the radius of the circle (in inches): ");
    radius = scanner.nextDouble();
    this.answer= answer(letterChosen);

}

public double areaCircle(double radius){

    // calculates the area of a circle
    area = Math.PI * Math.pow(radius, 2);
    return area;

}

public double areaSphere(double radius){

    // calculates the area of a sphere
    area = (4/3) * (Math.PI * Math.pow(radius, 3));
    return area;

}

public String answer(char letterChosen){

    //local variables
    String answer = "";
    if(letterChosen=='c'||letterChosen=='C'){
        answer = String.format("%s %f %s %.3f %s %n", "The volume of a circle with a radius of", radius, "inches is:", areaCircle(radius), "inches");
    }else{
        answer = String.format("%s %f %s %.3f %s %n", "The volume of a sphere with a radius of", radius, "inches is:", areaSphere(radius), "cubic inches");
    }
    return answer;
}

private static String goodbye(){

    // local variables
    String goodbye;

    // says and returns the goodbye message
    goodbye = String.format("%s", "Thank you for using the Round Object Calculator. Goodbye");
    return goodbye;
}

public static void main(String[] args) {

    // tells user what the program is about
    System.out.println("Welcome to the Round Object Calculator");
    System.out.println("This program will calculate the area of a circle of the colume of a sphere.");
    System.out.println("The calculations will be based on the user input radius.");
    System.out.println("");
    Module3Assignment1 ass1 = new Module3Assignment1();

        // loops while the user wants to calculate a round object
        while (useAgain == 'Y'||useAgain=='y'){

            ass1.input();
            System.out.print(answer);
            System.out.println("Do you want to calculate another round object (Y/N)? ");
            useAgain = scanner.next().charAt(0);
            System.out.println(useAgain);
            clearScreen();
        }

    // ending message/goodbye
    System.out.println(goodbye());
    scanner.close();

}

}

我改变的一些事情:

我用了字符 而不是 字符串 . 字符串 占用更多内存比 字符 .

添加了 clearScreen() 方法，当您使用控制台时“清除”屏幕。

我在 areaSphere 和 areaCircle 方法中添加了一个参数 radius。这使得方法可重用。

我将所有公共(public)静态变量更改为私有(private)静态。使用 公共(public)静态变量 是 强烈反对 .您可以阅读 this找出原因。

为了防止公共(public)静态变量，我创建了一个 Module3Assignment1 的实例，而不是将所有内容都放在静态中。

更改了方法名称的大小写。请遵循驼峰式，即方法首字母小写，其他单词首字母大写(如 input()、areaSphere() )

关于比较字符串的评论:

== compares REFERENCES TO THE OBJECT , NOT VALUES

使用 .equals() 或 .equalsIgnoreCase() 如果要比较两个字符串的值。这是一个示例语法:

if(string1.equals(string2)){
//do something
}