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 File_Read {
  public static void main(String[] args) {
    try {
      readFile("test1.txt");
    } catch (FileNotFoundException e) {
      System.out.println("Error: " + e.getMessage());
    }
  }

  public static void readFile(String fileName) throws FileNotFoundException {
    File file = new File(fileName);
    Scanner scanner = new Scanner(file);

    // Read and process the contents of the file
    while (scanner.hasNextLine()) {
      String line = scanner.nextLine();
      System.out.println(line);
    }

    scanner.close();
  }
}

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.

Flowchart:

Java Code Editor:

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