Exception Handling in Java

 

🔷 Introduction to Exception Handling in Java

Exception Handling in Java is a powerful mechanism that allows a program to detect and respond to run-time errors (exceptions) gracefully, without crashing the program.

Exceptions are unexpected events that disrupt the normal flow of a program, such as:

• Division by zero

• File not found

• Null pointer access

• Array index out of bounds

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✅ Why Exception Handling?

• To handle errors effectively and maintain normal application flow.

• To separate error-handling code from regular code.

• To provide meaningful error messages to users.

• To prevent program termination due to runtime errors.

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✅ Exception Handling Keywords

Keyword	Description
try	Defines a block of code to monitor for exceptions
catch	Defines a block to handle the exception
finally	Block that always executes, used for cleanup code
throw	Used to explicitly throw an exception
throws	Declares the exceptions a method might throw

🔁 Basic Example

public class Example {
    public static void main(String[] args) {
        try {
            int result = 10 / 0; // Will cause ArithmeticException
        } catch (ArithmeticException e) {
            System.out.println("Cannot divide by zero!");
        } finally {
            System.out.println("This always runs.");
        }
    }
}

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✅ Types of Exceptions

1. Checked Exceptions

• These are exceptions that are checked at compile-time.

• The compiler ensures that the programmer handles them.

• Must be caught using try-catch or declared using throws.

Examples:

• IOException

• SQLException

• ClassNotFoundException

import java.io.*;

public class CheckedExample {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
        System.out.println(reader.readLine());
    }
}

2. Unchecked Exceptions

• These occur at runtime and are not checked at compile-time.

• Caused by programming errors, and optional to handle.

Examples:

• ArithmeticException

• NullPointerException

• ArrayIndexOutOfBoundsException

public class UncheckedExample {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3};
        System.out.println(arr[5]); // ArrayIndexOutOfBoundsException
    }
}

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✅ Exception Class Hierarchy

java.lang.Object
    └── java.lang.Throwable
         ├── java.lang.Error         (serious problems, not handled)
         └── java.lang.Exception
              ├── Checked Exceptions (IOException, SQLException, etc.)
              └── Unchecked Exceptions (RuntimeException and its subclasses)