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Exception handling is a key aspect of building robust and maintainable Java applications. Java provides a structured way to detect and handle runtime errors using the try-catch-finally construct, exception classes, and custom exception mechanisms.

Exception Hierarchy in Java

At the top of Java’s exception hierarchy is the Throwable class, which has two main subclasses:

• Exception – Indicates conditions a program might want to catch.
• Error – Indicates serious problems that are not meant to be caught (e.g., OutOfMemoryError).

Subtypes of Exception:

• Checked Exceptions – Must be declared or handled (e.g., IOException, SQLException)
• Unchecked Exceptions – Runtime exceptions that don't require explicit handling (e.g., NullPointerException, ArrayIndexOutOfBoundsException)

Basic Syntax

java

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero.");
} finally {
    System.out.println("Cleanup if needed.");
}

• try: Block of code where exception may occur
• catch: Handles specific exception types
• finally: Runs regardless of exception (useful for resource cleanup)

Throwing and Creating Exceptions

Throwing an Exception:

java

if (input == null) {
    throw new IllegalArgumentException("Input cannot be null");
}

Creating a Custom Exception:

java

public class InvalidUserException extends Exception {
    public InvalidUserException(String message) {
        super(message);
    }
}

Checked vs Unchecked Exceptions

FeatureChecked ExceptionsUnchecked ExceptionsCompile-time checkYesNoSubclass ofExceptionRuntimeExceptionExampleIOException, ParseExceptionNullPointerException, IllegalArgumentException

Best Practices

• Catch specific exceptions instead of generic Exception.
• Avoid empty catch blocks – always log or handle errors meaningfully.
• Don’t swallow exceptions silently unless there's a valid reason.
• Use finally (or try-with-resources) for cleanup to avoid leaks.
• Throw custom exceptions to improve code readability and control flow.
• Wrap checked exceptions in unchecked ones when bubbling up in frameworks.

Try-With-Resources (Java 7+)

For automatic resource management:

java

try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
    String line = reader.readLine();
}

The reader is automatically closed, even if an exception occurs.

Common Pitfalls

• Relying on exceptions for control flow
• Catching Throwable or Error
• Ignoring exception stack traces
• Overusing checked exceptions in deep call stacks

Effective exception handling leads to better user experience, maintainable code, and easier debugging. By understanding Java's exception system and applying best practices, developers can write resilient and predictable applications.