===================
Step 0: start up
===================
import java.util.*;
import java.io.*;

public class Main {

    public static void main(String[] args) throws FileNotFoundException {
        Scanner in = new Scanner(System.in);
        System.out.print("Input the file pathname: ");
        String fname = in.next();

        Scanner inFile = new Scanner(new File(fname));
        int x = inFile.nextInt();
        inFile.close();
        System.out.println("Data is: " + x);
        System.out.print("Done.");

        in.close();
        System.out.print("Program ended.");
    }
}



// may throw FileNotFoundException !! (abc.txt)
// may throw InputMismatchException !! (data002.txt)

        NullPointerException, 
        ArrayIndexOutOfBoundsException, 
        ClassCastException, 
        StackOverflowError

===================
Step 1: processFile method
===================
import java.util.*;
import java.io.*;

public class Main {
	public static void processFile(String fname) throws FileNotFoundException {
		Scanner inFile = new Scanner(new File(fname));
		int x = inFile.nextInt();
		inFile.close();
		System.out.println("Data is: " + x);
	}

	public static void main(String[] args) throws FileNotFoundException {
		Scanner in = new Scanner(System.in);

		System.out.print("Input the file pathname: ");
		String fname = in.next();
		processFile(fname);
		System.out.print("Done.");
		
	        in.close();
        	System.out.print("Program ended.");
	}
}


// may throw FileNotFoundException !! (abc.txt)
// may throw InputMismatchException !! (data002.txt)

// NullPointerException
// ArrayIndexOutOfBoundsException 
// ClassCastException
// StackOverflowError

===================
Step 2: add exception handling
===================

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

public class Main {
	public static void processFile(String fname)
			throws FileNotFoundException {
		Scanner inFile = new Scanner(new File(fname));
		int x = inFile.nextInt();
		inFile.close();
		System.out.println("Data is: " + x);
	}

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		try {
			System.out.print("Input the file pathname: ");
			String fname = in.next();
			processFile(fname);
			System.out.print("Done.");
		} catch (FileNotFoundException e) {
			System.out.println("Cannot open the file.");
		} catch (InputMismatchException e) {
			System.out.println("Cannot read the required number from the opened file.");
		}

		in.close();
		System.out.print("Program ended.");
	}
}

//throws FileNotFoundException, InputMismatchException 

===================
Step 3: add negative integer checking
===================

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

public class Main {
	public static void processFile(String fname)
			throws FileNotFoundException, NegativeIntegerException {
		Scanner inFile = new Scanner(new File(fname));
		int x = inFile.nextInt();
		inFile.close();

		if (x < 0)
		 	throw new NegativeIntegerException();		
		System.out.println("Data is: " + x);
	}

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		try {
			System.out.print("Input the file pathname: ");
			String fname = in.next();
			processFile(fname);
		} catch (FileNotFoundException e) {
			System.out.println("Cannot open the file.");
		} catch (InputMismatchException e) {
			System.out.println("Cannot read the required number from the opened file.");
		} catch (NegativeIntegerException e) {
		 	System.out.println("Unexpected negative value from the file.");
		}

		System.out.print("Done.");
		in.close();
	}
}

=======================
class NegativeIntegerException extends Exception
{
	public NegativeIntegerException() { super("Negative integer!"); }
	
	public NegativeIntegerException(String message)	{ super(message); }
}