尝试并捕获Java中的错误

Question

I need to write a program that reads a text file and calculates different things, however, if the file name is not found, it should print an error message with the following error message from a try and catch block:

java.io.FileNotFoundException: inputValues (The system cannot find the file specfied)
    .......

However, I am instead receiving this error message:

Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at Project6.main(Project.java:50)

Here is part of my code:

Scanner console = new Scanner(System.in);                   
        System.out.print("Please enter the name of the input file: ");                              // Prompts User to Enter Input File Name
        String inputFileName = console.nextLine();                                                  // Reads Input File Name

        Scanner in=null;                                                                            // 

        try
            {
                in = new Scanner(new File(inputFileName));                                          // Construct a Scanner Object
            }
        catch (IOException e)                                                                       // Exception was Thrown
            {
                System.out.print("FileNotFound Exception was caught, the program will exit.");      // Error Message Printed because of Exception
                e.printStackTrace();
            }

        int n = in.nextInt();                                                                       // Reads Number of Line in Data Set from First Line of Text Document
        double[] array = new double[n];                                                             // Declares Array with n Rows

Line 50 is: int n = in.nextInt();

Other than printing the incorrect error message, my program runs perfectly fine.

Any/all help would be greatly appreciated!

Answer 1

Your exception thrown at the line in.nextInt() where you are trying to read an integer but the scanner found something else. If you need to take all of them as a single error you can put them in the same try catch block as follows.

Scanner in=null;                                                                            // 

    try
    {
        in = new Scanner(new File(inputFileName));   
        // Construct a Scanner Object
        int n = in.nextInt();                                                                         

        // Reads Number of Line in Data Set from First Line of Text Document
        double[] array = new double[n];
    } catch (IOException e)                                                                           
    // Exception was Thrown
    {
        System.out.print("FileNotFound Exception was caught, the program will exit.");      
        // Error Message Printed because of Exception
        e.printStackTrace();
     } catch (InputMismatchException e)                                                                         
     // Exception was Thrown
     {
        System.out.print("Integer not found at the beginning of the file, the program will exit.");      
        // Error Message Printed because of Exception
        e.printStackTrace();
     }

Answer 2

Ugly, badly formatted code is hard to read and understand. It's part of why you're having trouble.

This is simpler: start with this.

package cruft;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

/**
 * MessyFileDemo
 * @author Michael
 * @link https://stackoverflow.com/questions/31106118/try-and-catch-error-in-java
 * @since 6/28/2015 8:20 PM
 */
public class MessyFileDemo {

    public static void main(String[] args) {
        List<Double> values;
        InputStream is = null;
        try {
            String inputFilePath = args[0];
            is = new FileInputStream(inputFilePath);
            values = readValues(is);
            System.out.println(values);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            close(is);
        }
    }

    private static void close(InputStream is) {
        try {
            if (is != null) {
                is.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static List<Double> readValues(InputStream is) throws IOException {
        List<Double> values = new ArrayList<>();
        if (is != null) {
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            String line;
            while ((line = br.readLine()) != null) {
                String [] tokens = line.split(",");
                for (String token : tokens) {
                    values.add(Double.parseDouble(token));
                }
            }
        }
        return values;
    }

}