In this chapter, you will learn how to handle errors effectively using Java's standard libraries. Java offers powerful tools for managing problems that can occur during program execution. These tools include exceptions—special objects that help you detect and respond to errors—and a set of built-in classes such as IOException, RuntimeException, and IllegalArgumentException.

You will explore how these standard library features work, when to use them, and how they help you write more reliable, maintainable code. By the end of this chapter, you will understand the basics of Java error handling and be able to apply these techniques in your own projects.

Using Standard Java Exception Classes

Java provides several built-in exception classes to help you manage errors in your programs. Understanding how to use these standard exceptions—such as IOException, RuntimeException, and IllegalArgumentException—is important for writing reliable code.

IOException

Use IOException when you are working with input and output operations, such as reading from a file or network. This exception signals that something went wrong during these operations.

Example:

try {
    FileReader reader = new FileReader("data.txt");
    // Read from the file
    reader.close();
} catch (IOException e) {
    System.out.println("An error occurred while reading the file: " + e.getMessage());
}

RuntimeException

RuntimeException is the superclass for exceptions that can happen during the program's execution, often due to programming mistakes. These are unchecked exceptions, which means you do not have to catch them, but you can if you want to handle them gracefully.

Example:

try {
    int[] numbers = {1, 2, 3};
    System.out.println(numbers[5]); // This will throw an ArrayIndexOutOfBoundsException
} catch (RuntimeException e) {
    System.out.println("A runtime error occurred: " + e);
}

IllegalArgumentException

Use IllegalArgumentException to signal that a method has received an argument that is not valid. This helps you catch mistakes early and provide clear error messages.

Example:

public void setAge(int age) {
    if (age < 0) {
        throw new IllegalArgumentException("Age cannot be negative");
    }
    // Set the age
}

Best Practices for Handling Exceptions

• Catch only exceptions you can handle;
• Use meaningful error messages to help identify problems;
• Propagate exceptions when you cannot handle them by using throw or adding throws to the method signature.

By using standard exception classes and following these practices, you can make your Java programs more robust and easier to maintain.