When Should You Use Checked and Unchecked Exceptions in Java?

How do I determine whether to implement a custom exception as checked or unchecked in Java?

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

public class CustomUncheckedException extends RuntimeException {
    public CustomUncheckedException(String message) {
        super(message);
    }
}

In Java, exceptions are categorized into checked and unchecked exceptions. Choosing the right type for your custom exception class depends on the context in which the exception might occur and whether the caller can recover from it. The decision significantly impacts how exception handling is performed in your application, influencing its reliability and clarity.

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

public class InvalidUserInputException extends RuntimeException {
    public InvalidUserInputException(String message) {
        super(message);
    }
}

Causes

• **Nature of the Problem**: If the exception indicates a recoverable situation (e.g., file not found), it can be a checked exception. Unchecked exceptions typically signal programming errors (e.g., null pointer exceptions).
• **Caller Responsibility**: If the caller is expected to handle an exception contextually (like input validation errors), a checked exception is sensible. If the exception indicates a serious flaw that should not be recovered from (like logic errors), an unchecked exception is more appropriate.
• **Framework Compliance**: Certain frameworks might have conventions regarding exception handling, pushing developers toward using one type over the other.

Solutions

• **Use Checked Exception**: Opt for checked exceptions if you want to force the caller to handle the exception or declare it in their method signature. It's suitable for situations where there is a chance for recovery after handling the exception, such as in I/O operations.
• **Use Unchecked Exception**: Choose unchecked exceptions when it's unlikely the caller can remedy the situation or when signaling internal errors in the application's logic that should be avoided through better code practices rather than exception handling.

Mistake: Not clearly defining the recovery process for checked exceptions.

Solution: Ensure that your documentation guides the user on how to recover from the exception, making it clear what the expected handling should be.

Mistake: Using unchecked exceptions for scenarios that could be predictably handled by the caller.

Solution: Evaluate if the caller truly cannot recover from the error; if they can, revisit your design choice.

Mistake: Overusing checked exceptions leading to cluttered code with multiple try-catch blocks.

Solution: Use checked exceptions judiciously to avoid excessive boilerplate code.