Replacing Parts Without Breaking the Whole
In essence, the Liskov Substitution Principle promotes building a robust software ecosystem where interchangeable parts work seamlessly together, ensuring smooth operation and reliable functionality.
- Subtypes inherit the supertype's contract. They inherit the supertype's methods and properties, ensuring compatibility with existing code.
- Subtypes preconditions must be weaker or equal. The subtypes' methods can have weaker preconditions (accepting more input types) than the supertype, but not stricter ones.
- Subtypes postconditions must be stronger or equal. The subtypes' methods can have stronger postconditions (guaranteeing more output guarantees) than the supertype, but not weaker ones.
- Subtypes exceptions must be the same or subclasses of the supertype's exceptions. The subtypes' methods can throw only the same exceptions or subclasses of the exceptions thrown by the supertype.
- Improved code reuse Subtypes can leverage existing supertype code, reducing duplication and effort.
- Enhanced flexibility You can easily replace objects with different subtypes without rewriting the program.
- Increased reliability Substitutability guarantees program correctness even with changing types.
- Reduced testing effort Tests for the supertype can often apply to conforming subtypes.
- Use LSP when you have inheritance hierarchies and want to ensure type safety and program correctness.
- Overuse can lead to unnecessary complexity and overly restrictive subtype definitions.
- Design clear and concise contracts for both supertype and subtypes for efficient substitutability.