![]() ![]() There are many sources for this fattening, a common cause is misused inheritance. Your classes show problems regarding the ISP as soon as they start to fatten up and accommodate behaviors that aren't conceptually related. Packages of related behavior used by a single client should be split into smaller and more cohesive interfaces. Instead, it tries to protect the clients by ensuring that they don't know about all the behavior in the class. The ISP recognizes that sometimes these objects are needed. In reality, this is not always possible, and sometimes a big class can be extremely hard to chop into smaller ones. You might think that it would be better if instead of the BigClass we had smaller classes that implement each of the 3 new interfaces, and you are right. Now, each client depends only on the functionality they need. This leads to a structure that looks like this: We can refactor this design to follow the ISP by creating 3 smaller interfaces that encompass only the behavior used by each of the 3 clients. The three classes use only a portion of the functionality from the base class, but because they reference it, implicitly depend on a bunch of functionality they don't use. Now, there are 3 other object types ( ClientOne, ClientTwo and ClientThree) that use functionality from BigClass. Suppose that we have a big class with lots of functionality. ![]() Depending only on what you needĭepending on something that carries baggage that you don't need can cause you troubles that you didn't expect _Robert MartinĪpplying this idea to software design leads us to an obvious conclusion: an object should not depend on behavior it doesn't need. In summary, the ISP is a tool that guides you in the creation of well-defined interfaces and abstractions. ![]() The main benefit is the creation of consistent and granular abstractions. With current hardware, this is not much of an issue in most cases. Historically another reason to follow the ISP was the advantage recompiling fewer pieces of code when the referenced classes changed. Another benefit is that it lets you identify the right abstractions and build bundles of cohesive behavior. Removing unwanted dependencies and untangling our abstractions are some of our main goals when cleaning a software design. On one hand, it protects your objects from depending on things they don't need. It states that clients should not be forced to depend on functionality they don't use.įollowing this principle has several upsides. To do this, pull the methods currently in the view, and put them into a new interface called GameViewable.The interface segregation principle (ISP) is concerned with the way clients access the functionality developed in another class. Since you eventually want to implement a GUI for the view, you can extract an interface for the controller to interact with. How Do We Apply the Interface Segregation Principle to Our Code? Like single responsibility, high cohesion means that an interface describes one thing, very well. That makes that class less reusable.Īn interface that is well focused on what it should do is described as exhibiting high cohesion. The more an interface defines, the more an implementing class needs to do as well. Coupling refers to how closely connected two pieces of software are. Keeping interfaces small and to the point decreases coupling. Now all implementing classes have one more thing they have to account for. You need to add a new capability to an existing interface, rather than creating a new one. You can run into the same trouble with interfaces as with classes. It’s the same thing, only for interfaces:Īn interface should describe one set of behaviors. If you are comfortable with the single responsibility principle, the interface segregation principle will make perfect sense. ![]()
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