Patterns implementation

Implementation of several patterns in Java, which may be used as future example on how to technically implement them.

Database

DAO & DTO

Data Access Object & Data Transfer Object. DAO - Design pattern, used to encapsulate the access to a persistence resource (e.g a database) and eliminate dependencies which come with the implementation of the code. DTO is the object which representates an entity of the database, with all its own properties to be manipulated.

Structural

Façade

Helps with Model View Controller. Establishes a new layer to separate and encapsulate the code.

Singleton

Limits and sets a way to access an unique object instantiation during the whole execution of a program.

Behavioural

State

Allows to change the behaviour of an object through its own state. Depending the state the object is at, allows to manipulate it one way or another. Parts:

  • Context - It contains the action which will change depending on the current state. When called this action, it will delegate into the State object saved.
  • State Interface - Contains the design of the action. The context will save this raw.
  • Concrete States - Each one extends the interface and will override the action & its results.

Memento

Allows to restore an object to a previous state. It makes snapshots of the object and saves them, allowing later to restore any of them. Behaviour pattern. It does save snapshots of a class, to be able to recover a previous state of an object. Parts:

  • Originator - Class from which we save its states. e.g. a DTO.
  • Memento - It’s a Snapshot which saves the content of the Originator in a punctual state.
  • Caretaker - Class where we do save the several Mementos. From it we do save or load Mementos.

Creational

Builder

Allows to create beans easily (and fluently) for cases where we have lots of parameters (+4-5), with some of them required and others optional.

Factory

Uses factory methods to add an abstraction layout. Allows for example to be able to connect to several databases doing the swap by just changing two parameters in a config file.