SOLID Facts for Kids

SOLID is a helpful way to remember five important rules in software programming. These rules help programmers write computer code that is easy to understand, change, and fix later on. Even though SOLID principles are for object-oriented programming (a way of organizing code), they are also good ideas for other ways of developing software, like agile development.

The Five Principles of SOLID
How SOLID Started
See also

The Five Principles of SOLID

These principles are like guidelines for building strong and flexible software.

Single-Responsibility Principle

This rule means that each part of your code, like a class, should only have one job. If a class has too many jobs, it becomes hard to change without breaking something else. Imagine a robot arm that can only pick things up. If you want it to also paint, you'd build a separate painting tool, not make the picking-up arm also paint.

Open-Closed Principle

This principle says that your code should be "open for extension, but closed for modification." This means you should be able to add new features to your program without changing the existing, working code. Think of a game console: you can add new games (extend it) without changing the console itself (modifying it).

Liskov Substitution Principle

This rule is about how different parts of your code relate to each other. It means that if you have a main type of object, you should be able to use any of its specific versions without causing problems. For example, if you have a "Vehicle" type, and "Car" and "Truck" are specific versions of "Vehicle," then any code that works with a "Vehicle" should also work perfectly with a "Car" or a "Truck."

Interface Segregation Principle

This principle suggests that you should not force parts of your code to depend on things they don't use. It's better to have many small, specific sets of rules (called "interfaces") rather than one big, general set. Imagine a remote control: instead of one giant remote with buttons for every device in your house, you have separate, simpler remotes for the TV, the stereo, and the lights.

Dependency Inversion Principle

This rule means that your code should depend on general ideas (abstractions) rather than specific details (concretions). For example, instead of your game character directly depending on a specific "Sword" object, it should depend on a general "Weapon" idea. This way, you can easily swap out a "Sword" for an "Axe" or a "Bow" without changing the character's code.

How SOLID Started

A software engineer named Robert C. Martin first talked about these principles in a paper he wrote in the year 2000. He was thinking about how software can become messy and hard to manage over time, which he called "software rot." The word "SOLID" as an easy-to-remember acronym was created a few years later, around 2004, by Michael Feathers.

SOLID facts for kids

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