Category: - Software Development, Product to Market

Data Transfer Object Design Pattern

5/19/2020

overview

Data Transfer Object (DTO) is an object used to pass data with multiple items in one shot between client and server, to avoid client from issuing multiple calls to a remote server to get each item in separate calls.

Optionally, we can make use of a DTO Assembler class as some sort of a mapper in between DomainObject and DataTransferObject to map from one side to another in either direction. That is, to create a serializable DTO object given a Domain Object, or to update a Domain Object given a DTO object.

Inversion of Control / Dependency Injection Pattern

3/20/2020

People who just started to learn Spring framework is often confused by the term "Inversion of Control" (IoC) which can be achieved through "Dependency Injection" (DI).

DI is a way of providing the dependencies (e.g. creating objects and its dependencies), wiring components into application. In Spring, those objects defined and instantiated by Spring containers then inject into application are called Spring Beans.
IoC means to create instances of dependencies first. IoC is the end result of DI. However, DI is not the only way to achieve IoC.

Some good explanations:

Inversion of Control (IoC) means to create instances of dependencies first and latter instance of a class (optionally injecting them through constructor), instead of creating an instance of the class first and then the class instance creating instances of dependencies. Thus, inversion of control inverts the flow of control of the program. Instead of the callee controlling the flow of control (while creating dependencies), the caller controls the flow of control of the program.

~https://stackoverflow.com/questions/3058/what-is-inversion-of-control

IoC is a programming technique, expressed here in terms of object-oriented programming, in which object coupling is bound at run time by an assembler object and is typically not known at compile time using static analysis.

~http://en.wikipedia.org/wiki/Inversion_of_control

IoC is a common pattern in the Java community that helps wire lightweight containers or assemble components from different projects into a cohesive application.
~http://www.martinfowler.com/articles/injection.html (reworded)

Spring helps in the creation of loosely coupled applications because of Dependency Injection.

In Spring, objects define their associations (dependencies) and do not worry about how they will get those dependencies. It is the responsibility of Spring to provide the required dependencies for creating objects.

-https://stackoverflow.com/questions/9403155/what-is-dependency-injection-and-inversion-of-control-in-spring-framework

Flyweight Design Pattern Principle

6/15/2016

Flyweight pattern is a structural pattern in GoF as it supports large numbers of fine-grained objects efficiently. Since each fine-grained object (e.g. a character in an editor application) may incur overhead that adds up. This pattern shares objects in a pool (Flyweight Factory) to minimize memory use.

source: GoF

Composite and Prototype Design Pattern Example

4/21/2016

In a Composite (or Decorator) structure, Prototype uses a prototypical instance to create new Composite Component. Composite is a structural pattern where as Prototype is creational pattern. They are related to each other in a sense that Prototype only make sense in the context of a structural pattern like Composite or Decorator.

Composite (source: GoF)

Prototype source: GoF

Command Design Pattern Example

4/14/2016

Command pattern is a behavioral pattern in GoF as it allows us to decouple between the Invoker (a.k.a. sender, an object that invokes an operation) and the Receiver (an object that receives the request to execute a certain operation).

Also known as an action or transaction pattern.

Memento Design Pattern Example

8/28/2015

The word 'memento' refers to an object kept as a reminder or souvenir of a person or event. Memento pattern is a behavioral pattern in GoF because it captures and externalize an object's internal state so that the object can be restored to this state at a later time.

source: GoF

State Design Pattern Example

10/23/2013

State pattern is a behavioral pattern in GoF because it allows to alter its behavior when a context's internal state changes. The pattern handles each state using a separate state object and the transition from one state to another that does not call for if-then statements.

source: GoF

Chain of Responsibility Design Pattern Example

10/22/2013

Chain of Responsibility pattern is a behavioral pattern that sends data (a request, a Command) to an concrete handler object and if that handler object can't use/handle it, it passes the data/request to other objects along the chain until an handler object handles it.

source: GoF

Mediator Design Pattern Example

10/21/2013

Mediator pattern is a behavioral pattern that coordinates and encapsulates many-to-many communication/interaction among related objects (Colleagues) so that Colleagues interact not directly with other independent Colleagues, but indirectly with other Colleagues through a centralized Mediator.

source: GoF

Bridge Design Pattern Example

10/16/2013

Bridge pattern is categorized as a structural pattern in GoF because it structurally decouples abstraction from its implementation so that the two can vary independently. However, it is very similar to Strategy pattern which is categorized as a behavioral pattern.

source: GoF