问你在这段代码/程序中发现了什么错误？错误:它不会运行，除非你先输入一个数字

EN

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.
        }
    }
}

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

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.
}

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.
    }
}