🚨 Exception Handling in Java – Making Your Code More Reliable

🔖 Introduction

Even the best code can go wrong. A file might not be found, a number might be divided by zero, or user input could be invalid.

Java handles such unexpected events using Exception Handling — a powerful feature to manage runtime errors and avoid crashes.

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❓ What is an Exception?

An exception is an event that disrupts the normal flow of the program. Java provides a way to catch and handle these gracefully.

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🔹 Types of Exceptions

Type	Description	Example
Checked	Checked at compile time	IOException, SQLException
Unchecked	Occur during runtime	NullPointerException, ArithmeticException

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🧯 try-catch Block – Handle It Gracefully

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✅ Syntax:

try {
    // code that might throw an exception
} catch (ExceptionType name) {
    // handle the exception
}

📌 Example: Divide by Zero

public class Main {
    public static void main(String[] args) {
        try {
            int result = 10 / 0;  // risky
        } catch (ArithmeticException e) {
            System.out.println("Can't divide by zero!");
        }
    }
}

🔁 finally Block – Always Executes

Used for cleanup actions like closing files or database connections.

try {
    // code
} catch (Exception e) {
    // handling
} finally {
    System.out.println("This always runs!");
}

🚀 throw and throws – Custom and Propagated Exceptions

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🔹 throw – Throw an Exception Manually

public class AgeChecker {
    static void checkAge(int age) {
        if (age < 18) {
            throw new IllegalArgumentException("Underage not allowed!");
        }
    }
}

🔹 throws – Declare That a Method May Throw

public void readFile(String path) throws IOException {
    FileReader file = new FileReader(path);
}

🔨 Multiple catch Blocks

You can handle different exceptions separately:

try {
    String s = null;
    System.out.println(s.length());
} catch (NullPointerException e) {
    System.out.println("Null reference!");
} catch (Exception e) {
    System.out.println("Something went wrong!");
}

🧪 Challenge: Handle Array Index Exception

public class ArrayExample {
    public static void main(String[] args) {
        int[] nums = {1, 2, 3};
        try {
            System.out.println(nums[5]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Index out of bounds!");
        }
    }
}

🧠 Best Practices

• Catch specific exceptions first.
• Use finally to release resources.
• Avoid catching Exception blindly unless absolutely necessary.

✅ What You Learned

• What exceptions are and why they matter
• try, catch, finally, throw, and throws
• Handling both built-in and custom exceptions