Kotlin Crash Course for Programmers/

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Checked Exceptions vs Unchecked Exceptions

Checked Exceptions vs Unchecked Exceptions

Learn the difference between checked and unchecked exceptions and understand their pros and cons

We'll cover the following...

There are two types of exceptions:

  • Checked exceptions: the compiler forces you to catch them
  • Unchecked exceptions: you are free to catch them or not

Checked Exceptions

How does the compiler force you to handle checked exceptions?

Code Example

Because Kotlin has no checked exceptions, we will use Java to demonstrate the behavior. A function signature can indicate exceptions that it may throw:

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class CheckedExceptions {
    static String readFile(String path) throws IOException {
        return Files.readString(Paths.get(path));
    }
    
    public static void main(String[] args) {
        try {
            System.out.println(readFile("secrets.txt"));
        } catch (IOException e) {
            // Handle exception properly...
        }
    }
}

Here, the function signature of readFile indicates that it may throw an IOException – a checked exception in Java.

So when you call it, Java will force you to either:

  • Wrap the call in a try-block which has a catch-block that can handle a IOException.
  • Or add a throws declaration to the function that calls readFile. Then this same procedure applies again to that function.

Pros of Checked Exceptions

Checked exceptions are intended to make the code more robust and safe.

A checked exception will always be handled. This means it cannot bubble up to the top of the call stack and cause the program to crash so easily.

Cons of Checked Exceptions

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The major drawback of checked exceptions is that they distract developers from the actual logic. Oftentimes, the obligation to handle so many different exceptions makes developers simply swallow exceptions.

Of course, this is bad practice because it hides ...