Behavioral design patterns focus on communication between objects, and aim to provide a way to manage complex control flows between objects. Here is a brief overview of each of the behavioral design patterns:
- Chain of responsibility pattern: This pattern allows for the creation of a chain of objects that can handle a request, with the objects in the chain forwarding the request to the next object until it is handled. For example, a chain of responsibility class for handling customer service requests might have a method that receives the request, determines the appropriate handler for the request, and forwards the request to that handler.
- Command pattern: This pattern allows for the separation of an object that invokes an operation from the object that performs the operation. It consists of a class that represents the command and a separate class that executes the command. For example, a command class for performing database operations might have methods for inserting, updating, and deleting data, and a separate class would execute the appropriate command based on the request.
- Interpreter pattern: This pattern allows for the creation of an interpreter for a language or notation. It consists of a class that represents the grammar of the language and a separate class that interprets the grammar. For example, an interpreter class for parsing mathematical expressions might have methods for interpreting operations such as addition and subtraction, and a separate class would interpret a string containing a mathematical expression using the interpreter class.
- Iterator pattern: This pattern allows for the creation of a way to access the elements of an object sequentially without exposing the object’s underlying representation. It consists of a class that represents the iterator and a separate class that represents the object being iterated over. For example, an iterator class for a linked list might have methods for moving to the next element in the list and returning the current element, and a separate class would represent the linked list itself.
- Mediator pattern: This pattern allows for the creation of a way for objects to communicate indirectly, reducing the dependencies between them. It consists of a class that acts as a mediator between the objects, facilitating their communication. For example, a mediator class for a chat application might have methods for sending and receiving messages between users, and the users themselves would communicate indirectly through the mediator.
- Memento pattern: This pattern allows for the creation of a snapshot of an object’s state, allowing the object to be restored to that state later. It consists of a class that represents the memento and a separate class that creates and restores the memento. For example, a memento class for an undo/redo system might store the state of an object at a particular point in time, and a separate class would create a memento for the current state and restore a previous state from a memento when needed.
- Observer pattern: This pattern allows for the creation of a way for objects to be notified when the state of another object changes. It consists of a class that represents the observable object and a separate class that represents the observer. For example, an observer class for a stock ticker application might have a method that is called whenever the price of a particular stock changes, and a separate class would represent the stock and notify the observer when the price changes.
- State pattern: This pattern allows for the creation of a way for an object to change its behavior based on its internal state. It consists of a class that represents the state and a separate class that represents the context. For example, a state class for a vending machine might have methods for handling coin insertions and product selections, and a separate class would represent the vending machine and change its internal state based on the input it receives.
- Strategy pattern: This pattern allows for the selection of an algorithm at runtime. It consists of a class that represents the algorithm and a separate class that represents the context. For example, a strategy class for sorting a list of numbers might have methods for different sorting algorithms, and a separate class would represent the list and select the appropriate sorting algorithm based on the needs of the application.
- Template pattern: This pattern allows for the creation of a skeleton for an algorithm, with subclasses providing the implementation for specific steps. It consists of an abstract class that defines the template for the algorithm and concrete subclasses that implement the algorithm. For example, a template class for a cooking recipe might have an abstract “cook” method that defines the basic steps for preparing a dish, and concrete subclasses would implement the cook method with the specific steps and ingredients for a particular