Java Exception Handling?

Question

The following code calculates the average of numbers that are stored in a text file. I have added some exception handling for "file not found" errors. I need to know how to add another exception for when the data in the text file is not numeric (or not int). I thought about adding multiple catches. Not sure how though?

import java.util.*;
import java.io.*;

public class NumAvg2 {

    public static void main(String[] args)
    {
    int c = 1;  
    long sum = 0;
    String strFileName;

    strFileName = args[0];

    Scanner scFileData;
    try{
        scFileData = new Scanner (new File(strFileName));

        while (scFileData.hasNext())
        {
            sum = sum + scFileData.nextInt();
            c++;
        }

    scFileData.close();
    System.out.println("Number of integers: " + (c - 1)); 
    System.out.println( "Average = " + (float)sum/(c - 1));

    } catch (FileNotFoundException e) {
        System.out.println("File not found!");
        System.exit(1);
    }

  } 
}

you could read a string and try parsing. not good parsing well rays a error — elyashiv
– elyashiv, Commented Sep 26, 2012 at 19:17

RNJ · Accepted Answer · 2012-09-26 19:20:52Z

6

You can use Java 7's multi catch if you want

try {
...
}
catch (FileNotFoundException|InputMismatchException ex) {
//deal with exception
}

This is a bit cleaner than multiple catches. If either of these exceptions is thrown it is caught in the single catch block

answered Sep 26, 2012 at 19:20

RNJ

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4 Comments

FAUZI RASHID Over a year ago

This works: } catch (FileNotFoundException|InputMismatchException e) { System.out.println("Error Occured!"); System.out.println(e.getMessage()); System.exit(1); }

Chris Thompson Over a year ago

This is pretty...+1 for the new feature

user207421 Over a year ago

@FAUZIRASHID When you catch an exception, never just print your own message. Always print the one that comes with the exception. Otherwise you have no hope of knowing what the actual error was.

RNJ Over a year ago

@FAUZIRASHID, EJP makes a very good point. Also if it works then it is good etiquette to accept the answer...

Dmitry · Accepted Answer · 2012-09-26 19:20:52Z

3

} catch (InputMismatchException e) {
    System.out.println("Not integer!");
    System.exit(1);
} catch (FileNotFoundException e) {
    System.out.println("File not found!");
    System.exit(1);
}

answered Sep 26, 2012 at 19:20

Dmitry

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Comments

ecbrodie · Accepted Answer · 2012-09-26 19:27:05Z

3

...
} catch (FileNotFoundException e) {
    System.out.println("File not found!");
    System.exit(1);
} catch (InputMismatchException e) {
    // Add stuff into your new exception handling block
}
...

Your IDE may have not complained about this because InputMismatchException is a RuntimeException (unchecked exception), while FileNotFoundException is a regular checked Exception.

edited Sep 26, 2012 at 19:27

answered Sep 26, 2012 at 19:19

ecbrodie

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1 Comment

FAUZI RASHID Over a year ago

} catch (InputMismatchException e) { // Add stuff into your new exception handling block }

pb2q · Accepted Answer · 2014-06-04 00:31:46Z

3

Note that Scanner.nextInt also throws an InputMismatchException if the next token isn't an integer.

From the docs:

Throws: InputMismatchException - if the next token does not match the Integer regular expression, or is out of range

InputMismatchException is a RuntimeException, and so can be ignored in a try/catch block, but you can also explicitly handle it:

try
{
    // ... Scanner.nextInt
}
catch (FileNotFoundException e)
{
    System.out.println("File not found!");
    System.exit(1);
}
catch (InputMismatchException e)
{
    // ... not an int
}

edited Jun 4, 2014 at 0:31

answered Sep 26, 2012 at 19:18

pb2q

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Comments

Chris Thompson · Accepted Answer · 2012-09-26 19:19:17Z

2

To catch multiple exceptions, you chain them like so:

public class NumAvg2 {

public static void main(String[] args)
{
int c = 1;  
long sum = 0;
String strFileName;

strFileName = args[0];

Scanner scFileData;
try{
    scFileData = new Scanner (new File(strFileName));

    while (scFileData.hasNext())
    {
        sum = sum + scFileData.nextInt();
        c++;
    }

scFileData.close();
System.out.println("Number of integers: " + (c - 1)); 
System.out.println( "Average = " + (float)sum/(c - 1));

} catch (FileNotFoundException e) {
    System.out.println("File not found!");
    System.exit(1);
} catch(InputMismatchException e){
    //handle it
}
} 
}

answered Sep 26, 2012 at 19:19

Chris Thompson

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Comments

Ilya · Accepted Answer · 2012-09-26 19:20:44Z

1

} catch (FileNotFoundException | InputMismatchException e) {
    e.printStackTrace();
    System.exit(1);
}

answered Sep 26, 2012 at 19:20

Ilya

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Comments

Rohit Jain · Accepted Answer · 2012-09-26 20:10:45Z

1

Where are you converting your data from file to integer?? You should add one try-catch there..

Instead of using the below while loop, where you have to catch the exception for TypeMismatch: -

    while (scFileData.hasNext()) {
        try {
            sum = sum + scFileData.nextInt();
            c++;
        } catch (InputMismatchException e) {
            System.out.println("Invalid Input");
        }
    }

You can use a variation like the one below: -

    while (scFileData.hasNextInt())
    {
        sum = sum + scFileData.nextInt();
         c++;
    }

scanner.hasNextInt() will automatically check whether input in integer or not..

Also, as you are declaring your variable outside your try-catch block.. I would suggest not to use a big try-catch block..

Rather you can surround file reading statement around a try-catch (That would be one statement).. Then after a few statements, you can again surround your scanner.nextInt() around another try-catch..

So, I would modify your code like this: -

public class NumAvg2 {

public static void main(String[] args)
{
    int c = 1;  
    long sum = 0;
    String strFileName;

    strFileName = args[0];

    Scanner scFileData;

    try{
        scFileData = new Scanner (new File(strFileName));

    } catch (FileNotFoundException e) {
        System.out.println("File not found!");
        System.exit(1);
    }
    while (true) {
        if (scFileData.hasNextInt())
        {
            sum = sum + scFileData.nextInt();
            c++;
            break;
        } else {
            System.out.println("Enter an integr");
        }
    }

    scFileData.close();
    System.out.println("Number of integers: " + (c - 1)); 
    System.out.println( "Average = " + (float)sum/(c - 1));

}
}

This way your code becomes more cleaner.. * Just a Suggestion..

edited Sep 26, 2012 at 20:10

answered Sep 26, 2012 at 19:18

Rohit Jain

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4 Comments

FAUZI RASHID Over a year ago

OK. I got it to work using this method too. Added 2nd try/catch in the loop, but you have to also have to put a System.exit(1);

Rohit Jain Over a year ago

You don't need now.. see that I have used scanner.hasNextInt() in while.. It will automatically handle it.. It will only go inside the while if number is an integer..

Rohit Jain Over a year ago

See modified code.. I used an if now.. You don't need to do System.exit(1) if input is not an integer.. Just ask for input until an Integer is given..

FAUZI RASHID Over a year ago

Interesting way of doing it. Thanks!

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