03. Design Patterns

In Strategy pattern, a class behavior or its algorithm can be changed at run time. This type of design pattern comes under behavior pattern. In Strategy pattern, we create objects which represent various strategies and a context object whose behavior varies as per its strategy object. The strategy object changes the executing algorithm of the […]

In Null Object pattern, a null object replaces check of NULL object instance. Instead of putting if check for a null value, Null Object reflects a do nothing relationship. Such Null object can also be used to provide default behaviour in case data is not available. In Null Object pattern, we create an abstract class […]

In State pattern a class behavior changes based on its state. This type of design pattern comes under behavior pattern. In State pattern, we create objects which represent various states and a context object whose behavior varies as its state object changes. Implementation We are going to create a State interface defining an action and concrete state […]

Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified, its depenedent objects are to be notified automatically. Observer pattern falls under behavioral pattern category. Implementation Observer pattern uses three actor classes. Subject, Observer and Client. Subject is an object having methods to attach and detach observers […]

Memento pattern is used to restore state of an object to a previous state. Memento pattern falls under behavioral pattern category. Implementation Memento pattern uses three actor classes. Memento contains state of an object to be restored. Originator creates and stores states in Memento objects and Caretaker object is responsible to restore object state from […]

Mediator pattern is used to reduce communication complexity between multiple objects or classes. This pattern provides a mediator class which normally handles all the communications between different classes and supports easy maintenance of the code by loose coupling. Mediator pattern falls under behavioral pattern category. Implementation We are demonstrating mediator pattern by example of a […]

Iterator pattern is very commonly used design pattern in Java and .Net programming environment. This pattern is used to get a way to access the elements of a collection object in sequential manner without any need to know its underlying representation. Iterator pattern falls under behavioral pattern category. Implementation We’re going to create a Iterator interface which […]

Interpreter pattern provides a way to evaluate language grammar or expression. This type of pattern comes under behavioral pattern. This pattern involves implementing an expression interface which tells to interpret a particular context. This pattern is used in SQL parsing, symbol processing engine etc. Implementation We are going to create an interface Expression and concrete classes implementing […]

Command pattern is a data driven design pattern and falls under behavioral pattern category. A request is wrapped under an object as command and passed to invoker object. Invoker object looks for the appropriate object which can handle this command and passes the command to the corresponding object which executes the command. Implementation We have […]

As the name suggests, the chain of responsibility pattern creates a chain of receiver objects for a request. This pattern decouples sender and receiver of a request based on type of request. This pattern comes under behavioral patterns. In this pattern, normally each receiver contains reference to another receiver. If one object cannot handle the […]