Custom Exceptions

Declaring Custom Exceptions allows you to expose domain-specific error states. When creating custom exceptions, you should extend the appropriate base exception and implement standard constructors that support exception chaining.

Writing the Standard Exception Constructors

To fully support standard Java patterns, a custom exception should implement:

1. No-Argument Constructor: public MyException() { super(); }
2. Message Constructor: public MyException(String message) { super(message); }
3. Cause Constructor (for Chaining): public MyException(Throwable cause) { super(cause); }
4. Message & Cause Constructor: public MyException(String message, Throwable cause) { super(message, cause); }

Common Pitfalls

• Omitting the Cause Constructor: Creating custom exceptions that only accept a message, which prevents exception chaining and discards the root cause stack trace.
• Over-creating Custom Exceptions: Creating a new custom class for every single error scenario instead of reusing standard Java exceptions (like IllegalArgumentException).

Best Practices

• Suffix with Exception: Always end custom exception class names with the suffix Exception (e.g. PaymentException).
• Prefer Unchecked: Extend RuntimeException for custom exceptions unless callers must recover programmatically.

Interview-Relevant Information