Java 您在该代码/程序中发现了什么错误？除非你先输入一个数字，否则它不会运行

所以我的问题是： 这个程序用来计算圆的面积 用户输入一个数字，然后给出答案 此外，任何无效的输入是不允许的，我使用的尝试捕捉，但它不会工作

非常感谢大家抽出时间：））

代码如下：

import java.util.Scanner; 
import java.io;

/**
 *
 * @author Osugule
 */
public class AreaCircle { 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
Scanner sc = new Scanner(System.in); // read the keyboard
System.out.println("This program will calculate the area of a circle");
System.out.println("Enter radius:");//Print to screen
double r = sc.nextDouble(); // Read in the double from the keyboard
double area = (3.14 *r * r); 
try {

}
catch( NumberFormatException e ) {
    System.out.println("Invalid Input, please enter a number");
    //put a message or anything you want to tell the user that their input was weird.
}

String output = "Radius: " + r + "\n";
output = output + "Area: " + area + "\n";
System.out.println("The area of the circle  is " + area);

    }
}

---

你应该把这两行

double r = sc.nextDouble(); // Read in the double from the keyboard
double area = (3.14 *r * r); 

在

try

块内-

import java.util.Scanner; 
import java.io;

/**
*
* @author Osugule
*/
public class AreaCircle
{ 
    /**
    * @param args the command line arguments
    */
    public static void main(String[] args)
    {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in); // read the keyboard
        System.out.println("This program will calculate the area of a circle");            
        boolean correct_input = false;

        while(correct_input == false)
        {
            System.out.println("Enter radius:");//Print to screen
            try
            {
                double r = sc.nextDouble(); // Read in the double from the keyboard
                double area = (3.14 *r * r); 
                String output = "Radius: " + r + "\n";
                output = output + "Area: " + area + "\n";
                System.out.println("The area of the circle  is " + area);
                correct_input = true;
            }
            catch( NumberFormatException e )
            {
                System.out.println("Invalid Input, please enter a number");
                //put a message or anything you want to tell the user that their input was weird.
            }
            catch( InputMismatchException e )
            {
                System.out.println("Input Mismatch, please enter a number");
                //put a message or anything you want to tell the user that there is an 
                //input mismatch.
            }
        }

    }
}

catch( NumberFormatException e )
{
    System.out.println("Invalid Input, please enter a number");
    //put a message or anything you want to tell the user that their input was weird.
}

// New catch block 
catch( InputMismatchException e )
{
    System.out.println("Input Mismatch, please enter a number");
    //put a message or anything you want to tell the user that there is an 
    //input mismatch.
}

从—

public double nextDouble（）

将输入的下一个标记扫描为双精度标记。如果无法将下一个标记转换为有效的双精度值，则此方法将抛出InputMismatchException。如果翻译成功，扫描仪将通过匹配的输入

抛出：

InputMismatchException-如果下一个标记与浮点正则表达式不匹配， 或者超出范围

NoTouchElementException-如果输入已耗尽

IllegalStateException-如果此扫描仪已关闭

因此，如果输入了无效字符，

sc.nextDouble（）

可能会抛出一个

InputMismatchException

，该异常不会被

catch

块捕获，因为它只包含catcher

NumberFormatException

。因此，您的程序将在抛出异常后终止，但您不会收到任何消息

要处理此情况，请在当前

catch

块下方添加以下块-

import java.util.Scanner; 
import java.io;

/**
*
* @author Osugule
*/
public class AreaCircle
{ 
    /**
    * @param args the command line arguments
    */
    public static void main(String[] args)
    {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in); // read the keyboard
        System.out.println("This program will calculate the area of a circle");            
        boolean correct_input = false;

        while(correct_input == false)
        {
            System.out.println("Enter radius:");//Print to screen
            try
            {
                double r = sc.nextDouble(); // Read in the double from the keyboard
                double area = (3.14 *r * r); 
                String output = "Radius: " + r + "\n";
                output = output + "Area: " + area + "\n";
                System.out.println("The area of the circle  is " + area);
                correct_input = true;
            }
            catch( NumberFormatException e )
            {
                System.out.println("Invalid Input, please enter a number");
                //put a message or anything you want to tell the user that their input was weird.
            }
            catch( InputMismatchException e )
            {
                System.out.println("Input Mismatch, please enter a number");
                //put a message or anything you want to tell the user that there is an 
                //input mismatch.
            }
        }

    }
}

catch( NumberFormatException e )
{
    System.out.println("Invalid Input, please enter a number");
    //put a message or anything you want to tell the user that their input was weird.
}

// New catch block 
catch( InputMismatchException e )
{
    System.out.println("Input Mismatch, please enter a number");
    //put a message or anything you want to tell the user that there is an 
    //input mismatch.
}

---

你应该把这两行

double r = sc.nextDouble(); // Read in the double from the keyboard
double area = (3.14 *r * r); 

在

try

块内-

import java.util.Scanner; 
import java.io;

/**
*
* @author Osugule
*/
public class AreaCircle
{ 
    /**
    * @param args the command line arguments
    */
    public static void main(String[] args)
    {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in); // read the keyboard
        System.out.println("This program will calculate the area of a circle");            
        boolean correct_input = false;

        while(correct_input == false)
        {
            System.out.println("Enter radius:");//Print to screen
            try
            {
                double r = sc.nextDouble(); // Read in the double from the keyboard
                double area = (3.14 *r * r); 
                String output = "Radius: " + r + "\n";
                output = output + "Area: " + area + "\n";
                System.out.println("The area of the circle  is " + area);
                correct_input = true;
            }
            catch( NumberFormatException e )
            {
                System.out.println("Invalid Input, please enter a number");
                //put a message or anything you want to tell the user that their input was weird.
            }
            catch( InputMismatchException e )
            {
                System.out.println("Input Mismatch, please enter a number");
                //put a message or anything you want to tell the user that there is an 
                //input mismatch.
            }
        }

    }
}

catch( NumberFormatException e )
{
    System.out.println("Invalid Input, please enter a number");
    //put a message or anything you want to tell the user that their input was weird.
}

// New catch block 
catch( InputMismatchException e )
{
    System.out.println("Input Mismatch, please enter a number");
    //put a message or anything you want to tell the user that there is an 
    //input mismatch.
}

从—

public double nextDouble（）

将输入的下一个标记扫描为双精度标记。如果无法将下一个标记转换为有效的双精度值，则此方法将抛出InputMismatchException。如果翻译成功，扫描仪将通过匹配的输入

抛出：

InputMismatchException-如果下一个标记与浮点正则表达式不匹配， 或者超出范围

NoTouchElementException-如果输入已耗尽

IllegalStateException-如果此扫描仪已关闭

因此，如果输入了无效字符，

sc.nextDouble（）

可能会抛出一个

InputMismatchException

，该异常不会被

catch

块捕获，因为它只包含catcher

NumberFormatException

。因此，您的程序将在抛出异常后终止，但您不会收到任何消息

要处理此情况，请在当前

catch

块下方添加以下块-

import java.util.Scanner; 
import java.io;

/**
*
* @author Osugule
*/
public class AreaCircle
{ 
    /**
    * @param args the command line arguments
    */
    public static void main(String[] args)
    {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in); // read the keyboard
        System.out.println("This program will calculate the area of a circle");            
        boolean correct_input = false;

        while(correct_input == false)
        {
            System.out.println("Enter radius:");//Print to screen
            try
            {
                double r = sc.nextDouble(); // Read in the double from the keyboard
                double area = (3.14 *r * r); 
                String output = "Radius: " + r + "\n";
                output = output + "Area: " + area + "\n";
                System.out.println("The area of the circle  is " + area);
                correct_input = true;
            }
            catch( NumberFormatException e )
            {
                System.out.println("Invalid Input, please enter a number");
                //put a message or anything you want to tell the user that their input was weird.
            }
            catch( InputMismatchException e )
            {
                System.out.println("Input Mismatch, please enter a number");
                //put a message or anything you want to tell the user that there is an 
                //input mismatch.
            }
        }

    }
}

catch( NumberFormatException e )
{
    System.out.println("Invalid Input, please enter a number");
    //put a message or anything you want to tell the user that their input was weird.
}

// New catch block 
catch( InputMismatchException e )
{
    System.out.println("Input Mismatch, please enter a number");
    //put a message or anything you want to tell the user that there is an 
    //input mismatch.
}

---

我编辑了答案，这样它会再次询问用户输入是否错误

您需要在try子句中添加nextDouble：

boolean inputProcessed = false;
while (!inputProcessed) {
    try {
        double r = sc.nextDouble(); // Read in the double from the keyboard
        double area = (3.14 *r * r); 
        String output = "Radius: " + r + "\n";
        output = output + "Area: " + area + "\n";
        System.out.println("The area of the circle  is " + area);
        // this indicates that we were able to process the input, and we should stop now.
        inputProcessed = true; 
    }
    catch( NumberFormatException e ) {
        System.out.println("Invalid Input, please enter a number");
        //put a message or anything you want to tell the user that their input was weird.
    }
}

---

请注意，我在try子句中添加了try catch之后的行，好像您无法解析数字一样，它们不应该被打印出来。

我编辑了答案，这样它会再次询问用户输入是否错误

您需要在try子句中添加nextDouble：

boolean inputProcessed = false;
while (!inputProcessed) {
    try {
        double r = sc.nextDouble(); // Read in the double from the keyboard
        double area = (3.14 *r * r); 
        String output = "Radius: " + r + "\n";
        output = output + "Area: " + area + "\n";
        System.out.println("The area of the circle  is " + area);
        // this indicates that we were able to process the input, and we should stop now.
        inputProcessed = true; 
    }
    catch( NumberFormatException e ) {
        System.out.println("Invalid Input, please enter a number");
        //put a message or anything you want to tell the user that their input was weird.
    }
}

---

请注意，我在try子句中添加了try catch之后的行，就好像您无法解析数字一样，它们不应该被打印。

您必须捕获

InputMismatchException

异常，如下所示：

import java.util.InputMismatchException;
import java.util.Scanner; 
public class AreaCircle { 
    public static void main(String[] args) {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in); // read the keyboard
        System.out.println("This program will calculate the area of a circle");
        System.out.println("Enter radius:");//Print to screen
        try {
            double r = sc.nextDouble(); // Read in the double from the keyboard
            double area = (3.14 *r * r);

            String output = "Radius: " + r + "\n";
            output = output + "Area: " + area + "\n";
            System.out.println("The area of the circle  is " + area);

        }
        catch( InputMismatchException e ) {
            System.out.println("Invalid Input, please enter a number");
            //put a message or anything you want to tell the user that their input was weird.
        }
        catch( NumberFormatException e ) {
            System.out.println("Invalid Input, please enter a number");
            //put a message or anything you want to tell the user that their input was weird.
        }
    }
}

---

您必须捕获如下异常：

import java.util.InputMismatchException;
import java.util.Scanner; 
public class AreaCircle { 
    public static void main(String[] args) {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in); // read the keyboard
        System.out.println("This program will calculate the area of a circle");
        System.out.println("Enter radius:");//Print to screen
        try {
            double r = sc.nextDouble(); // Read in the double from the keyboard
            double area = (3.14 *r * r);

            String output = "Radius: " + r + "\n";
            output = output + "Area: " + area + "\n";
            System.out.println("The area of the circle  is " + area);

        }
        catch( InputMismatchException e ) {
            System.out.println("Invalid Input, please enter a number");
            //put a message or anything you want to tell the user that their input was weird.
        }
        catch( NumberFormatException e ) {
            System.out.println("Invalid Input, please enter a number");
            //put a message or anything you want to tell the user that their input was weird.
        }
    }
}

---

---

我建议养成使用

Math.PI

而不是

3.14

的习惯，你是第一次编码吗？？首先理解代码的含义！是的，不是第一次，但我刚开始我建议养成使用

Math.PI

而不是

3.14

的习惯你是第一次编码吗？？首先理解代码的含义！是的，不是第一次，但我刚刚开始OK，很好，非常感谢…但是当我运行程序并输入无效的字母时，程序就结束了？程序结束了，因为异常捕获程序正在捕获坏异常并继续执行到最后。如果您希望程序再次提示用户，则需要将整个

try/catch

块放入while循环中。好的，非常感谢……但当我运行程序并输入无效字符时，程序刚刚结束？程序结束，因为异常捕获器刚刚捕获坏异常并继续执行到结束。如果您希望程序再次提示用户，则需要将整个

try/catch

块放入while循环中。如果我在其中放入无效字符，为什么程序刚好结束？@user1190386:可能是抛出

输入不匹配异常

。查看编辑。@user1190386:请让我知道它是否有效：-）。非常感谢，我真的很感激。我现在对学习java非常陌生。对不起，我还有一个问题。。。。当我输入一个无效的输入时，它会显示消息，程序会停止..我需要使用while循环吗？如果我输入了一个无效的字符，为什么程序会结束？@user1190386:可能它抛出了

InputMismatchException

。查看编辑。@user1190386:请让我知道它是否有效：-）。非常感谢，我真的很感激。我现在对学习java非常陌生。对不起，我还有一个问题。。。。当我输入无效输入时，它会显示消息，程序停止..我需要使用while循环吗？当用户输入错误输入时，程序会停止吗？当用户输入错误输入时，程序会停止吗？？