- Design patterns are typical solutions to common problems in software design. Each pattern is like a blueprint that you can customize to solve a particular design problem in your code.
- Patterns are a toolkit of solutions to common problems in software design. They define a common language that helps your team communicate more efficiently.
These patterns provide various object creation mechanisms, which increase flexibility and reuse of existing code.
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Provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.
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Creates an instance of several derived classes
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Lets you produce families of related objects without specifying the concrete classes
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Creates an instance of several families of classes
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Let you construct complex objects step by step. The pattern allows you to produce different types and representations of an object using the same construction code.
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Separates object construction from its representation
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Lets you copy exist objects without making your code dependent on their classes.
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A fully initialized instance to be copied or cloned
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Lets you ensure that a class has only one instance while providing a global access point to this instance.
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A class of which only a single instance can exist
Avoid expensive acquisition and release of resources by recycling objects that are no longer in use
These patterns explain how to assemble objects and classes into larger structures while keeping these structures flexible and efficient.
- Allows object with incompatible interface to collaborate
- Match interfaces of different classes
- Separates an object's interface from its implementation
- Lets you split a large class or set of closely related classes into two separate hierarchies abstraction and implementation which can be developed independently of each other
- Lets you compose objects into tree structures and then work with these structures as if the were individual objects.
- A tree structure of simple and composite objects
- Add responsibilities to objects dynamically
- Lets you attach new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors
- Provides a simplified interface to a library, a framework, or any other complex set of classes
- A single class that represents an entire subsystem
- A fine-grained instance used for efficient sharing
- Lets your fit more objects into the available amount of RAM by sharing common parts of state between multiple objects instead of keeping all of the data in each object
- Lets you provide a substitute or placeholder for another object. A proxy control access to the original object, allowing you to perform something either before or after the request gets through to the original object.
- An object representing another object
- Restricts accessor/mutator access
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These patterns are concerned with algorithms and the assignment of responsibilities between objects.
- A way of notifying change to a number of classes
- Lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they're observing.
- A way of passing a request between a chain of objects
- Lets you passs request along a chain of handlers. Upon receiving a request, each handler decides either to process the request or to pass it to the next handler in the chain
- Turns a request into a stand-alone object that contain all information about the request. This transformation lets you pass request as a method argument, delay or queue a request's execution, and support undoable operations
- Encapsulate a command request as an object
- Sequentially access the elements of a collection
- Lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.)
- Lets you reduce chaotic dependencies between objects. The pattern restricts direct communications between the objects and forces them to collaborate only via mediator object
- Defines simplified communication between classes
- Capture and restore an object's internal state
- Lets you save and restore the previous state of an object without revealing the details of its implementation
- Lets and object alter its behavior when its internal state changes. It appears as if the object changed its class.
- Alter an object's behavior when its state changes
- Encapsulates an algorithm inside a class
- Lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
- Define the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
- Defer the exact steps of an algorithm to a subclass
- Defines a new operation to a class without change
- Lets you separate algorithms form the object on which thet operate.
- A way to include language elements in a program
- Designed to act as a default value of an object
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