When you are writing code, things don't always go as planned. Sometimes, unexpected errors pop up, like a file not being found or a network failure. To handle these situations, Java provides a structured approach – an exception handling mechanism.
In this post, we’ll break down how exception handling works in Java, what types of exceptions you should be aware of, and how to write code that’s both clean and error-proof. Whether you’re just starting out or you've been coding for a while, getting a handle on exception handling will help keep your app in top shape. Let’s get into it!"
What Is Exception Handling in Java?
Exception handling in Java is a mechanism that allows developers to handle runtime errors effectively. With proper exception handling, developers can ensure the smooth execution of a program. It will help you if you come across unexpected issues during the program execution. Java provides you with an effective mechanism for handling exceptions. In this way, you can write an error-resistant code.
try: This is where you write the code that might cause an error. You basically "try" to run that code, and Java watches for any problems that come up.
catch: If an error happens in the try block, the catch block steps in. It lets you handle that specific error and prevent the app from crashing.
finally: No matter what happens -- whether an error occurred or not -- the code in the finally block will always run. It's a good place to put any cleanup code, like closing a file.
throw: This lets you manually create an throw an error if something goes wrong. For example, if a certain condition is met, you can throw an exception to signal that something is not right.
Types of Exceptions in Java
Java categorizes exceptions into two main types:
1. Checked Exceptions
These are exceptions that Java forces you to deal with. When you write code that might cause a checked exception, Java checks it while you're writing the program (this is called compile time).
You have two choices for handling these exceptions:
- Catch them using a try-catch block to prevent the program from crashing.
- Declare them in the method you’re working on with the throws keyword, which tells Java that the exception might occur in that method and should be handled somewhere else.
If you don’t handle or declare a checked exception, Java will show an error and not let your program run. Examples include errors like IOException (problems with input/output operations) or SQLException (issues when working with databases).
Examples:
● IOException
● SQLException
Example Usage:
`public void readFile(String filePath) throws IOException {
Files.readString(Path.of(filePath));
}`
2. Unchecked Exceptions
Unchecked Exceptions (also known as runtime exceptions) happen while the program is running. These types of errors usually happen because of bugs or mistakes in the code, like trying to use something that doesn’t exist (e.g., a NullPointerException) or trying to access an array with an invalid index (e.g., ArrayIndexOutOfBoundsException).
Java doesn’t make you handle these exceptions. The program will crash if the error happens, but you don’t need to explicitly catch or declare them in your code. However, it's still a good idea to handle them if you can, to make your program more stable and prevent it from crashing unexpectedly.
Examples:
● NullPointerException
● IllegalArgumentException
Example Usage:
`public void validateInput(String input) {
if (input == null || input.isBlank()) {
throw new IllegalArgumentException("Input cannot be null or blank");
}
}`
Best Practices for Exception Handling
Handling exceptions in Java isn’t just about catching errors – it’s about doing it right. Throwing a try-catch block around everything might seem like a quick fix, but if you’re not careful, it can lead to messy, hard-to-maintain code. Exception handling needs to be done thoughtfully to keep your app stable and your code clean.
In this section , we’ll walk through some of the best practices that will help you handle exceptions effectively.
1. Use Specific Exceptions
Why? Catching specific exceptions makes your code much clearer and easier to debug. When you use a generic Exception, you lose valuable details about what went wrong. By catching specific exceptions, like FileNotFoundException or SQLException, you can address each error scenario individually, providing more targeted solutions.
Example:
`try {
Files.readString(Path.of("nonexistent-file.txt"));
} catch (NoSuchFileException e) {
System.out.println("File not found: " + e.getMessage());
} catch (IOException e) {
System.out.println("An I/O error occurred: " + e.getMessage());
}`
Explanation:
In this example, the code is trying to read the contents of a file using Files.readString(). The file in question is "nonexistent-file.txt," which may not exist on the system. By using specific exception handling, the program can respond differently depending on the type of error.
The first catch block specifically catches a NoSuchFileException. This exception is thrown when the file is not found. In this case, the program prints a clear message: "File not found," followed by the exception's message.
If any other IOException occurs (such as issues with file permissions or input/output errors), the second catch block catches it. This ensures that other types of I/O errors are handled separately and gives a more general error message: "An I/O error occurred," followed by the relevant message.
2. Leverage Record Patterns for Exception Details
Java's record patterns allow you to easily extract and work with relevant details from exception objects. Instead of dealing with complex exception messages, you can deconstruct an exception into its specific components, making it easier to handle and respond to the exact nature of the issue.
Example:
`record CustomError(int code, String message) {}
try {
throw new IllegalArgumentException(new CustomError(404, "Resource not found").toString());
} catch (IllegalArgumentException e) {
if (e.getMessage().contains("404")) {
System.out.println("Specific handling for 404 error: " + e.getMessage());
} else {
System.out.println("General error: " + e.getMessage());
}
}`
Explanation:
In this example, a custom error class is defined using a record called CustomError. This record holds two pieces of information: an int representing an error code and a String for an error message. The advantage of using a record here is that it allows for a simple, immutable object that neatly encapsulates error details.
- In the try block, an IllegalArgumentException is thrown with a CustomError object converted to a string. This string contains both the error code (404) and the message ("Resource not found").
- In the catch block, the code checks if the exception message contains the error code 404. If it does, the program handles the exception in a specific way by printing a customized message: "Specific handling for 404 error." If the error code isn't 404, the program defaults to a general error handling message: "General error."
3. Utilize Structured Concurrency for Multi-threaded Errors
In a multi-threaded environment, it is not easy to handle exceptions, as errors can happen in different places. And you may find it hard to track and manage. Structured concurrency helps you simplify this, as you can control how threads are launched.
Let's say you're running multiple threads to process data. Using structured concurrency, if one thread throws an exception, you can catch and handle it within the context of that thread, preventing it from affecting others.
Example:
`import java.util.concurrent.*;
public class StructuredConcurrencyExample {
public static void main(String[] args) {
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
Future<String> result1 = scope.fork(() -> {
if (Math.random() > 0.6) throw new RuntimeException("Task 1 failed");
return "Task 1 completed";
});
Future<String> result2 = scope.fork(() -> "Task 2 completed");
scope.join();
scope.throwIfFailed();
System.out.println(result1.resultNow());
System.out.println(result2.resultNow());
} catch (Exception e) {
System.out.println("Error in one of the tasks: " + e.getMessage());
}
}
}`
Explanation:
In this example, we use StructuredTaskScope to manage two tasks running in separate threads. Each task is "forked" (started) within this scope, and we ensure that if one task fails, the entire scope will shut down, avoiding further errors or resource leaks.
Here’s how it works:
- We start two tasks inside the scope. One task has a 40% chance of failing (throwing an exception), while the other task always completes successfully.
- If any task fails, the scope handles it gracefully. The scope.join() method waits for all tasks to finish. If an error occurs, scope.throwIfFailed() ensures the exception is caught and handled properly.
- If any task fails, the exception is caught in the outer try-catch block, and an error message is printed. If everything goes well, we print the results of the tasks.
4. Handle Resources with Try-with-Resources
When you are working with file streams or database connections, it is crucial to avoid leaks. The try-with-resources statement can make this easy. It automatically closes resources like files or database connections, even if an exception occurs.
This way, you don’t have to worry about manually closing resources, and you can ensure your code runs smoothly without leaving behind any unnecessary open connections.
Example:
`try (var reader = Files.newBufferedReader(Path.of("example.txt"))) {
reader.lines().forEach(System.out::println);
} catch (IOException e) {
System.out.println("Error reading file: " + e.getMessage());
}`
Explanation:
This code reads the file example.txt line by line using a BufferedReader. The try-with-resources statement automatically handles closing the BufferedReader once the task is done, even if an error happens. You don’t need to manually close the resource in a finally block, which keeps the code simple and easy to maintain.
Additional Tips to Avoid Common Pitfalls
Even with best practices, certain mistakes can undermine effective exception handling. Here are common pitfalls to avoid:
1. Don’t Swallow Exceptions
Bad Practice:
`try {
riskyOperation();
} catch (Exception e) {
// Do nothing
}`
Why to Avoid
Where exceptions are caught by an empty catch block, the real cause of an error is hidden, making debugging harder and perhaps leading to an application continuing in an inconsistent state.
Better Approach
In any case, always treat the exceptions appropriately, either by logging the error, retrying the operation, or informing the user.
2. Use Custom Exceptions Wisely
Creating custom exceptions adds clarity, but then to be used judiciously so that they add context and meaning to your error handling.
Example:
`class InvalidUserInputException extends RuntimeException {
public InvalidUserInputException(String message) {
super(message);
}
}
public void validateInput(String input) {
if (input == null || input.isBlank()) {
throw new InvalidUserInputException("Input cannot be null or blank");
}
}`
Explanation:
In this case, a custom exception, InvalidUserInputException, clearly indicates what an error is about. It talks about invalid user input, which makes it easier for it to understand and properly deal with as per the requirement elsewhere in the application.
Enhanced NullPointerException Logging in Latest Java Versions
One of the most common problems in Java is NullPointerException. In recent versions of Java, logging for NPEs has been made better to give more specific information about what exactly was null, making debugging much easier.
Example:
`public class NullPointerExceptionExample {
public static void main(String[] args) {
String text = null;
try {
System.out.println(text.length());
} catch (NullPointerException e) {
System.out.println("NullPointerException caught: " + e.getMessage());
e.printStackTrace();
}
}
}`
Enhanced Logging Explanation:
The new Java versions, on occurrence of NullPointerException, will provide more detailed information about the variable that is null. This way, developers will be able to easily determine the source of the null reference without having to look at the code line by line.
Sample Enhanced Stack Trace:
`Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.length()" because "text" is null
at NullPointerExceptionExample.main(NullPointerExceptionExample.java:5)`
Explanation:
The better-improved exception message clearly states that the text variable is null, which immediately tells one what caused the exception. Debugging time is reduced, thereby increasing overall code reliability.
Conclusion
In this article, we've covered how exception handling works in Java and how to effectively manage exceptions. We’ve also explored the different types of exceptions, shared best practices, and highlighted how to avoid common pitfalls. I hope you found this guide useful. For more valuable insights and easy-to-understand explanations, be sure to keep visiting Brilworks. If you're looking to improve your code’s performance, we’re here to help.
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