How to correctly use try-catch-finally blocks in Java?

Question

What would be the proper way to use the finally block to close out of the file that I was in : event.dat. If you could help me makes sense of this, I'd greatly appreciate it. I've literally spent 4 hours moving things around, playing with the code and searching for answers online, but to no avail. Code works great without that portion, but I need to know how it works for future instances. Thank you and have a good day!

I am having issues with this block:

          finally{
              fstream.close();        
          } 

Which is located in the following code:

    String answer;
    String letter;
    String inType = "";
    double inAmount = 0;
    double amount;

    description();
    GironEventClass newInput = new GironEventClass();
    try{
        File infile = new File("event.dat");
        Scanner fstream = new Scanner(infile);

        System.out.println("File Contents ");

        while(fstream.hasNext())
        {
            inAmount = fstream.nextInt();
            inType = fstream.next();

            try{
                newInput.donations(inType, inAmount);

            }
            catch(IllegalArgumentException a){
                System.out.println("Just caught an illegal argument exception. ");
            }  
           finally{
                   fstream.close();        
          }  
        }

        System.out.println("Total Sales: " + newInput.getSale());
        System.out.println("Donations: " + newInput.getDonated());
        System.out.println("Expenses: " + newInput.getExpenses());



    }

    catch (FileNotFoundException e){
        System.out.println("\nEvent.dat could not be opened. ");
    }

    do{
        System.out.print("Are there any more items to add that were not in the text file? (Type 'Y' or 'N')");
        answer = keyboard.next();
        if (("Y".equals(answer)) || ("y".equals(answer)))
        {
            letter = inLetter();
            amount = inAmount();

            newInput.donations(letter, amount);
        }

    }while (("Y".equals(answer)) || ("y".equals(answer)));

    newInput.display();
}

public static String inLetter(){
    Scanner keyboard = new Scanner(System.in);
    String result;
    String resultTwo;

    System.out.println("T = Tiket Sales");
    System.out.println("D = Donations");
    System.out.println("E = Expenses");
    System.out.print("Please input an identifier ");
    result = keyboard.nextLine();
    resultTwo = result.toUpperCase();

    return resultTwo;    
}

public static double inAmount(){
    Scanner keyboard = new Scanner(System.in);
    double result;

    System.out.println("Please input an amount ");
    result = keyboard.nextInt();

    if(result <= 0.0){
        System.out.print("Please input a positive and non-zero amount ");
        result = keyboard.nextInt();
    }

    return result;
}

public static void description(){
    System.out.println("The program will ask you what amount is being spent on what.");
    System.out.println("    ex: expenses, ticket sales, and profts.");
    System.out.println("This program will help determine whether the event generated or lost money.");      
}

Answer 1

The Try block attempts to do something.

The Catch block only executes if something went wrong during the Try block.

The Finally block executes after the Try block (and Catch block, if executed) EVERY time.

Your issue is that you attempt to close the fstream inside the while loop.

while(fstream.hasNext())  <----- referencing fstream
        {
            inAmount = fstream.nextInt();
            inType = fstream.next();

            try{
                newInput.donations(inType, inAmount);

            }
            catch(IllegalArgumentException a){
                System.out.println("Just caught an illegal argument exception. ");
            }  
           finally{
                   fstream.close();        <---- closing said stream
          }  
        }

Since you've closed the stream, this while loop should only ever execute once. That being said, close the fstream outside the while loop and your program should return to normal.

You can also move the while loop inside the try block, which would work as well.

Answer 2

This is how the scanner should work:

while scanner has object
   read them ( one object per method's call) 
when objects are done
   close the reader.

Your problem is that you use the close function when the while conclusion is true. So you should put it outside of the while loop

Answer 3

You need to declare fstream outside the try block otherwise it will be not visible in the finally block.

File infile = null;
File infile = null;
try {
    infile = new File("event.dat");
    fstream = new Scanner(infile);

    ...
} catch ( ) {
    ...
} finally {
   // You need to handle exceptions also here
   infile.close();
   fstream.close();
}

You can also use the new try with resources syntax and leave to the jvm the closure of your streams.