Scanner.nextLine() throws an Exception, if I close the first Scanner and create a new Scanner

Question

I want to implement a programm, which reads two strings from the user input.

        try 
    {
        System.out.println( "please enter a valid URL ( i.e. http://www.uibk.ac.at )" );
        Scanner inputScanner = new Scanner( System.in );
        String urlString = inputScanner.next(); 
        asciiTable = new int[NUM_ASCII_CHAR];
        URL url = new URL( urlString );
        URLConnection connection = url.openConnection();
        connection.connect();
        InputStreamReader in = new InputStreamReader( url.openStream() );
        countCharactersfromFile( in );
        printAsciiTable( asciiTable );
        printNumberOfChars( asciiTable );
        inputScanner.close();
        in.close();
    }
    // it has not the form of an URL
    catch ( MalformedURLException e ) 
    {
        e.printStackTrace();
    }
    // If the site cannot be connected
    catch( UnknownHostException e )
    {
        e.printStackTrace();
    }
    // some IO-Error occurs
    catch ( IOException e ) 
    {
        e.printStackTrace();
    }
    // if the ASCII array is empty
    catch( EmptyListException e )
    {
        e.printStackTrace();
    }
    catch( IllegalArgumentException e )
    {
        e.printStackTrace();
    }
    catch ( Exception e ) 
    {
        e.printStackTrace();
    }
    try
    {
        System.out.println( "Please enter the name of a file " );
        asciiTable = new int[NUM_ASCII_CHAR];
        Scanner scanner = new Scanner( System.in );
        String fileString = scanner.next();
        FileInputStream fileStream = new FileInputStream( fileString );
        InputStreamReader in = new InputStreamReader( fileStream );
        countCharactersfromFile( in );
        printAsciiTable( asciiTable );
        printNumberOfChars( asciiTable );
        scanner.close();        
    }
    catch ( IOException e ) 
    {
        e.printStackTrace();
    }
    catch( EmptyListException e )
    {
        e.printStackTrace();
    }
    catch( IllegalArgumentException e )
    {
        e.printStackTrace();
    }
    catch ( Exception e ) 
    {
        e.printStackTrace();
    }

At first I want to let you know that I know the problem. I should only use 1 Scanner in my program. But if use only one try block in my program, i am not allowed to execute the 2nd part of the task, if an exception is thrown. I have a solution, but I do not know if it is a good one.

try
{
    Scanner inputScanner = new Scanner( System.in );
    try
    {
        //the URL code, use inputScanner here
    }
    catch()
    {

    }
    try
    {
        // The file code, use inputscanner here
    }
    catch()
    {

    }
    inputscanner.close();
}
catch()

Is the solution, which is shown above a good one? Or do you have some better solutions for my problem.

Thanks Patrik

`scanner.close()` will close the standard `System.in` stream as well. close it in the end only. — Braj, Jun 01 '14 at 18:45
your try catch blocks are so cumbersome. why don't you use try catch block with resources? — Kick Buttowski, Jun 01 '14 at 18:53

score 2 · Accepted Answer · answered Jun 01 '14 at 19:14

To make sure Scanner is always closed, wrap all code using it into a try block and close it in finally block afterwards:

Scanner inputScanner = new Scanner(System.in);
try {
    try {
        // 1st operation
    } catch (Exception e) {
        System.err.println("1st operation failed");
    }
    try {
        // 2nd operation
    } catch (Exception e) {
        System.err.println("2nd operation failed");
    }
} finally {
    inputScanner.close();
}

Or use try-with-resource, which will do the same:

try (Scanner inputScanner = new Scanner(System.in)) {
    ...
}

It might be better not to close inputScanner at all. You will not be able to read anything else from standard input. Scanner doesn't consume any additional system resources so you can let garbage collector worry about it.

Additional tip: Do not catch exceptions, if you are not doing anything useful with them. Just let them propagate. You can even declare main method to throw an Exception.

Scanner.nextLine() throws an Exception, if I close the first Scanner and create a new Scanner

1 Answers1