Java Program: File reading and exception handling for positive numbers

Java Exception Handling: Exercise-4 with Solution

Write a Java program that reads a list of numbers from a file and throws an exception if any of the numbers are positive.

Sample Solution:

Java Code:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class Positive_Number_Check {
    public static void main(String[] args) {
        try {
            checkNumbersFromFile("test.txt");
            System.out.println("All numbers are non-positive.");
        } catch (FileNotFoundException e) {
            System.out.println("Error: " + e.getMessage());
        } catch (PositiveNumberException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
    public static void checkNumbersFromFile(String fileName) throws FileNotFoundException, PositiveNumberException {
        File file = new File(fileName);
        Scanner scanner = new Scanner(file);
        while (scanner.hasNextLine()) {
            int number = Integer.parseInt(scanner.nextLine());
            if (number > 0) {
                throw new PositiveNumberException("Positive number found: " + number);
            }
        }
        scanner.close();
    }
}
class PositiveNumberException extends Exception {
    public PositiveNumberException(String message) {
        super(message);
    }
}

Sample Output:

Content of test.txt:
-1
-2
-3
-4

All numbers are non-positive.

Content of test.txt:
-1
-2
-3
4

Error: Positive number found: 4

Explanation:

The above code demonstrates how to read numbers from a file and throw a custom exception if any are positive. It showcases the use of exception handling and the creation of custom exceptions in Java.

Here are some important points:

• The PositiveNumberException class is a custom exception class that extends the base Exception class. It provides a constructor that takes a message parameter and passes it to the superclass constructor using the super keyword.
• If a FileNotFoundException occurs in the main method, it is caught and an appropriate error message is printed.
• If a PositiveNumberException occurs in the checkNumbersFromFile method, it is caught in the main method. The error message indicating a positive number is printed.

Java Code Editor:

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