Question

My problem lies with trying to access Scanner scan created in one method from another method. It says it cannot find variable scan. I tried declaring a global Scanner scan, but it gave me an error, non static variable name cannot be referenced from a static context. How can I access this variable?

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

public class MyClass {
    public static void myMethod() {
        final File f = new File("file.txt");
        Scanner scan = null;
        try {
            scan = new Scanner(f);
        }
        catch(FileNotFoundException ex) {
            System.exit(0);
        }
    }

    public static boolean anotherMethod() {
        final String s = scan.next ();

        if (s.equalsIgnoreCase ("true"))  return true;
        if (s.equalsIgnoreCase ("false")) return false;

        throw new java.util.InputMismatchException ();
    }
}

Answer 1

You’ve only declared the scan variable within the flow method. If you want to use that value within the other methods, you’ll need to take one of two courses of action:

• Declare it as a non-local variable
• Pass it into those other methods via a parameter

As all your methods are static, for the first option you’d need to declare it as:

private static Scanner scan;

However, currently the flow method seems to do two radically different things:

• It creates the Scanner (but doesn’t actually use it)
• It tries to use data which it expects to have already been read

It looks to me like you should be creating the Scanner in your main method (or in a new method which is called before readBoolean2D, anyway). You’re currently calling readBoolean2D as the very first action of the program, trying to read from a variable which doesn’t exist, before any Scanner has even been created.

Note that none of this has anything to do with the try block itself – it’s the fact that the variable is declared in a separate method which is the problem (and the timing of the method calls), not the try block.

I would try to think of restructuring the program as:

• Open input
• Read all the data
• Process all the data

I suspect you can actually get away with just local variables and parameters – the first method would return a Scanner; the second method would take a Scanner and return the data it reads; the third method would take the data.