What Are Design Patterns ?
Design pattern is nothing but a general solution to a variety of similar problems ...
In software engineering , a design pattern is a general reusable solution to a commonly occurring problem in software design . A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations.Object Oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved.
Design patterns are represented as relationships between classes and objects with defined responsibilities that act in concert to carry out the solution. To illustrate a design pattern, consider the Adapter pattern, one of the original 23 patterns described in Design Patterns. Adapter provides a solution to the scenario in which a client and server need to interact with one another, but cannot because their interfaces are incompatible. To implement an Adapter, you create a custom class that honors the interface provided by the server and defines the server operations in terms the client expects. This is a much better solution than altering the client to match the interface of the server.
Benefits of Design Patterns
Design patterns have two major benefits. First, they provide you with a way to solve issues related to software development using a proven solution. The solution facilitates the development of highly cohesive modules with minimal coupling. They isolate the variability that may exist in the system requirements, making the overall system easier to understand and maintain. Second, design patterns make communication between designers more efficient. Software professionals can immediately picture the high-level design in their heads when they refer the name of the pattern used to solve a particular issue when discussing system design.Types of Design Patterns
Design patterns are mainly of three types
Creational
Structural
Behavioral
Creational patterns are ones that create objects for you,rather than having you instantiate objects directly. This gives your program more flexibility in deciding which objects need to be created for a given case.
Structural patterns help you compose groups of objects into larger structures, such as complex user interfaces or accounting data.
Behavioral patterns help you define the communication between objects in your system and how the flow is
controlled in a complex program.
Java Design Pattern
Creational Patterns
• Abstract Factory:- Creates an instance of several families of classes
• Builder: - Separates object construction from its representation
• Factory Method:- Creates an instance of several derived classes
• Prototype:- A fully initialized instance to be copied or cloned
• Singleton:- A class in which only a single instance can exist
• Builder: - Separates object construction from its representation
• Factory Method:- Creates an instance of several derived classes
• Prototype:- A fully initialized instance to be copied or cloned
• Singleton:- A class in which only a single instance can exist
Note: - The best way to remember Creational pattern is by remembering ABFPS (Abraham Became First President of States).
Structural Patterns
Structural Patterns
• Adapter:-Match interfaces of different classes .
• Bridge:-Separates an object’s abstraction from its implementation.
• Composite:-A tree structure of simple and composite objects.
• Decorator:-Add responsibilities to objects dynamically.
• Façade:-A single class that represents an entire subsystem.
• Flyweight:-A fine-grained instance used for efficient sharing.
• Proxy:-An object representing another object.
• Bridge:-Separates an object’s abstraction from its implementation.
• Composite:-A tree structure of simple and composite objects.
• Decorator:-Add responsibilities to objects dynamically.
• Façade:-A single class that represents an entire subsystem.
• Flyweight:-A fine-grained instance used for efficient sharing.
• Proxy:-An object representing another object.
Note : To remember structural pattern best is (ABCDFFP)
Behavioral Patterns
Behavioral Patterns
• Mediator:-Defines simplified communication between classes.
• Memento:-Capture and restore an object's internal state.
• Interpreter:- A way to include language elements in a program.
• Iterator:-Sequentially access the elements of a collection.
• Chain of Resp: - A way of passing a request between a chain of objects.
• Command:-Encapsulate a command request as an object.
• State:-Alter an object's behavior when its state changes.
• Strategy:-Encapsulates an algorithm inside a class.
• Observer: - A way of notifying change to a number of classes.
• Template Method:-Defer the exact steps of an algorithm to a subclass.
• Visitor:-Defines a new operation to a class without change.
Note: - Just remember Music....... 2 MICS On TV (MMIICCSSOTV).• Memento:-Capture and restore an object's internal state.
• Interpreter:- A way to include language elements in a program.
• Iterator:-Sequentially access the elements of a collection.
• Chain of Resp: - A way of passing a request between a chain of objects.
• Command:-Encapsulate a command request as an object.
• State:-Alter an object's behavior when its state changes.
• Strategy:-Encapsulates an algorithm inside a class.
• Observer: - A way of notifying change to a number of classes.
• Template Method:-Defer the exact steps of an algorithm to a subclass.
• Visitor:-Defines a new operation to a class without change.
Java Design Pattern
Swapna, very informative article.
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