Imagine you have a class called Chef that represents a chef in a restaurant system. Let's apply SOLID principles to this class in a funny way:
Single Responsibility Principle (SRP):
The Chef class should have only one reason to change. In other words, it should only be responsible for one thing, like cooking. We don't want our Chef class to also handle things like managing the restaurant's finances or serving tables. Otherwise, you might end up with a chef who's too busy calculating the daily profits to actually cook anything!
Open/Closed Principle (OCP):
The Chef class should be open for extension but closed for modification. So, if you want to add a new type of cuisine, you shouldn't have to modify the Chef class itself. Instead, you should be able to extend it by creating a new subclass like ItalianChef or SushiChef. Otherwise, you might find yourself in a situation where every time you want to introduce a new dish, you have to rewrite the entire menu!
Liskov Substitution Principle (LSP):
Subclasses should be substitutable for their base classes. For example, if you have a SushiChef subclass of Chef, you should be able to substitute a SushiChef object wherever you would normally use a Chef object. Otherwise, you might end up with a sushi chef who refuses to cook anything that's not fish-related, even if the customer requests a simple salad!
Interface Segregation Principle (ISP):
Clients should not be forced to depend on interfaces they do not use. In other words, if a client only needs to interact with a subset of a class's functionality, they shouldn't be forced to depend on the entire class. Otherwise, you might have a situation where a customer who just wants to order a sandwich ends up being bombarded with options for every type of cuisine imaginable, from burgers to sushi!
Dependency Inversion Principle (DIP):
High-level modules should not depend on low-level modules. Both should depend on abstractions. In our Chef example, this means that the Chef class shouldn't depend directly on specific ingredients or cooking utensils. Instead, it should depend on abstractions like Ingredient and CookingTool, allowing for flexibility and easier testing. Otherwise, you might end up with a chef who refuses to cook anything unless they have their favorite brand of olive oil and a specific type of spatula, even if other ingredients and tools are perfectly suitable!