Java Exception Handling – Practical Scenarios Explained

#java #programming #beginners #tutorial

Exception handling in Java is not just about catching errors, but about designing programs that behave predictably even when things go wrong. Let’s explore three important real-world scenarios to understand how exceptions should be used effectively.

1.Student Result System

Problem Statement

You are building a system to store student marks. The valid range is between 0 and 100.

Conditions

If marks < 0 → throw exception
If marks > 100 → throw exception

public class StudentResult {
    public static void main(String[] args) {
        int marks = 110; 

        if (marks < 0 || marks > 100) {
            throw new IllegalArgumentException("Invalid marks! Marks should be between 0 and 100 ");
        }

        System.out.println("Valid marks: " + marks);
    }
}

This uses an unchecked exception (IllegalArgumentException)
It is appropriate because invalid marks indicate a programming or input validation issue
The program immediately stops when invalid data is detected, preventing incorrect results

2.Checked vs Unchecked Exceptions – When to Use?

Checked

Checked exceptions are used when the error is expected and recoverable.

Java forces you to handle them using try-catch or throws. For example, opening a file may throw an IOException, and the program can recover by asking for another file.

FileReader file = new FileReader("test.txt"); // IOException

When to Use

The error is expected
The error is recoverable
The caller should be forced to handle it

Unchecked

Unchecked exceptions are used for programming mistakes that are not recoverable at runtime.

These occur due to logical errors in code, like dividing by zero, which throws an ArithmeticException. Instead of handling them, the correct approach is to fix the code.

int a = 10 / 0; // ArithmeticException

When to Use

The error is due to a programming mistake
It is not recoverable at runtime
No need to force handling

3.Will finally Execute if System.exit(0)is Called? (To be discussed)

When System.exit(0) runs, it immediately shuts down the JVM, like pulling the plug on the entire program. Because of this sudden stop, the normal flow of execution is interrupted, and the finally block is skipped completely.

public class TestFinally {
    public static void main(String[] args) {
        try {
            System.out.println("Try block");
            System.exit(0);
        } finally {
            System.out.println("Finally block");
        }
    }
}