SOLID is a set of five design principles that can be used to create more robust, maintainable, and extensible software. The principles are:
- Single Responsibility Principle: A class or module should have only one reason to change.
- Open/Closed Principle: Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.
- Liskov Substitution Principle: Derived types should be substitutable for their base types.
- Interface Segregation Principle: Clients should not be forced to depend on methods they do not use.
- Dependency Inversion Principle / Inversion of Control: High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions.
Some real-life examples,
- Single Responsibility Principle: A car is an example of a system that follows the SRP. The car has many different components, such as the engine, the transmission, the brakes, and the wheels. Each of these components has a single responsibility. For example, the engine’s responsibility is to provide power to the car. The transmission’s responsibility is to transfer power from the engine to the wheels.
- Open/Closed Principle: A software application that allows users to customize their user interface is an example of a system that follows the OCP. The application can be extended to support new customization options without having to modify the existing code. This makes the application more flexible and adaptable to change.
- Liskov Substitution Principle: A car is an example of a system that satisfies the LSP. A car can be replaced by a different car, such as a truck or a van, without affecting the rest of the system. This is because all cars have the same basic functionality, such as the ability to transport people and cargo.
- Interface Segregation Principle: A software application that allows users to choose which features they want to use is an example of a system that follows the ISP. The application provides a number of different features, such as the ability to create documents, the ability to send emails, and the ability to edit spreadsheets. Users can choose which features they want to use, which makes the application more user-friendly and less overwhelming.
- Dependency Inversion Principle / Inversion of Control: A software application that uses a database to store data is an example of a system that follows the DIP. The application does not depend on the specific database that is used. Instead, it depends on an interface that defines the methods that the database must implement. This allows the application to be used with any database that implements the interface.