Design patterns are recurring solutions to common software design problems. They are generally considered to be the best practices for solving common software design challenges. In this article, we will introduce ten common design patterns and their applications.
Chain of Responsibility
The Chain of Responsibility is a behavioral pattern that allows a system to process a request through a chain of handlers. Each handler can decide whether to handle the request or pass it to the next handler in the chain.
The core of the Chain of Responsibility is organizing the processing objects into a chain, where each processing object can decide whether to process the request or pass it on to the next processing object.
Command
The Command is a behavioral pattern that decouples the requester of a command from the object that executes the command, allowing them to vary independently.
The core of the Command is encapsulating a command into an object and passing it to the receiver for execution. The Command pattern can implement features such as undo and redo.
Interpreter
The Interpreter is a behavioral pattern that defines a set of grammar rules and uses those rules to interpret expressions.
The core of Interpreter is decomposing the grammar into small expression objects and allowing them to interpret the expressions. By combining the expression objects, an interpreter tree can be created to parse complex grammars.
Iterator
The Iterator is a behavioral pattern that provides a mechanism for traversing the elements of a collection without exposing its underlying structure.
The core of the Iterator is abstracting the traversal operation of the collection and defining a common traversal interface, allowing different collections to implement it separately. By doing this, the traversal operation is separated from the collection itself.
Mediator
The Mediator is a behavioral pattern that resolves complex relationships between multiple objects, improving system maintainability and extendibility.
The core of the Mediator is abstracting the object interactions into a mediator object responsible for coordinating the interactions. By doing this, object interactions can be isolated from each other, reducing system complexity.
Memento
The Memento is a behavioral pattern that provides a way to capture and restore an object’s state without violating its encapsulation.
The core of the Memento is defining a memento object to hold the object’s state and delegating the responsibility of managing the memento object to the caretaker. By doing this, object state restoration can be achieved without breaking object encapsulation.
Observer
The Observer is a behavioral pattern that defines a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated automatically.
The core of the Observer is defining abstract observer and subject interfaces, allowing concrete observer and subject objects to implement them. By doing this, object coupling can be reduced and system flexibility and extendibility can be improved.
State
The State is a behavioral pattern that changes an object’s behavior based on its state.
The core of the State is abstracting the object state into its own object, then decoupling the state object and its context to enable dynamic behavior changes. By doing this, we can avoid traditional if-else statements and improve the maintainability and extendibility of the system.
Strategy
The Strategy is a behavioral pattern that defines a series of algorithms and encapsulates them into separate strategy objects, allowing them to be interchanged.
The core of the Strategy is abstracting the different algorithms into separate strategy objects and allowing the client to choose the specific strategy object needed for a particular task. By doing this, we can dynamically switch between different algorithms and improve system flexibility and extendibility.
Template Method
The Template Method is a behavioral pattern that defines a skeleton of an algorithm and allows subclasses to provide concrete implementations of some methods.
The core of the Template Method is defining the algorithm skeleton and delegating parts of the implementation to its subclasses. By doing this, we can avoid repeating code, enhance code reusability and maintainability, and extend the algorithm via hook methods.
In conclusion, in this article, we’ve summarized ten common design patterns and their applications, introducing their core ideas and use cases. We hope this information helps you choose the best design pattern for your specific problem, improving your design quality and code efficiency.