Design Patterns | Set 1 (Introduction) - GeeksforGeeks

Design Patterns | Set 1 (Introduction) - GeeksforGeeks

Design pattern is a general reusable solution or template to a commonly occurring problem in software design. The patterns typically show relationships and interactions between classes or objects. The idea is to speed up the development process by providing tested, proven development paradigm.

 
Goal:
• Understand the problem and matching it with some pattern.
• Reusage of old interface or making the present design reusable for the future usage.

 
Example:
For example, in many real world situations we want to create only one instance of a class. For example, there can be only one active president of country at a time regardless of personal identity. This pattern is called Singleton pattern. Other software examples could be a single DB connection shared by multiple objects as creating a separate DB connection for every object may be costly. Similarly, there can be a single configuration manager or error manager in an application that handles all problems instead of creating multiple managers.

 
Types of Design Patterns
There are mainly three types of design patterns:

 
1. Creational
These design patterns are all about class instantiation or object creation. These patterns can be further categorized into Class-creational patterns and object-creational patterns. While class-creation patterns use inheritance effectively in the instantiation process, object-creation patterns use delegation effectively to get the job done.

Creational design patterns are Factory Method, Abstract Factory, Builder, Singleton, Object Pool, Prototype and Singleton.

 
2. Structural
These design patterns are about organizing different classes and objects to form larger structures and provide new functionality.

Structural design patterns are Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Private Class Data and Proxy.

 
3. Behavioral
Behavioral patterns are about identifying common communication patterns between objects and realize these patterns.

Behavioral patterns are Chain of responsibility, Command, Interpreter, Iterator, Mediator, Memento, Null Object, Observer, State, Strategy, Template method, Visitor

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