What is the difference between checked and unchecked exceptions?

Checked exceptions (like IOException) must be caught or declared in the method signature. Unchecked exceptions (subclasses of RuntimeException, like NullPointerException) don't have to be, and usually indicate programming errors.

Should I catch the generic Exception class?

Usually not. Catching specific exceptions makes your intent clear and avoids hiding unrelated bugs. Reserve broad catches for top-level handlers that log and report.

Exception Handling in Java: try, catch, finally

Introduction

Things go wrong at runtime: files go missing, input is invalid, networks fail. Java's exception handling lets you detect these problems and respond instead of crashing. This tutorial covers try/catch/finally, try-with-resources, and throwing exceptions yourself.

Prerequisites

JDK installed
Basic Java syntax and methods

Step-by-Step Guide

Step 1: Catch an exception with try/catch

Put risky code in a try block and handle the problem in a matching catch block. Catch the most specific exception type you can.

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero: " + e.getMessage());
}

Step 2: Run cleanup code with finally

Code in a finally block runs whether or not an exception occurred, which makes it useful for cleanup.

try {
    int[] numbers = {1, 2, 3};
    System.out.println(numbers[5]);
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Invalid index");
} finally {
    System.out.println("This always runs");
}

Step 3: Close resources with try-with-resources

Resources that implement AutoCloseable, such as readers and streams, are closed automatically when declared in the try parentheses. IOException is a checked exception, so you must catch it or declare it.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

try (BufferedReader reader = new BufferedReader(new FileReader("data.txt"))) {
    System.out.println(reader.readLine());
} catch (IOException e) {
    System.out.println("Could not read file: " + e.getMessage());
}

Step 4: Throw your own exceptions

Use throw to signal invalid input or state. Choose an exception type that describes the problem.

public static void setAge(int age) {
    if (age < 0) {
        throw new IllegalArgumentException("Age cannot be negative");
    }
    System.out.println("Age set to " + age);
}

FAQs

What is the difference between checked and unchecked exceptions?: Checked exceptions (like IOException) must be caught or declared in the method signature. Unchecked exceptions (subclasses of RuntimeException, like NullPointerException) don't have to be, and usually indicate programming errors.
Should I catch the generic Exception class?: Usually not. Catching specific exceptions makes your intent clear and avoids hiding unrelated bugs. Reserve broad catches for top-level handlers that log and report.

Summary

Catch specific exceptions, clean up with finally or try-with-resources, and throw meaningful exceptions for invalid input. Handled well, errors become predictable instead of fatal.