Java design patterns: definition and types

Design patterns definition

A design pattern is a repeatable solution to a commonly occurring software design problem. However, a design pattern is not a finished design that can be directly copied into your code. It is not a specific piece of code but a general concept or template for solving a specific problem, applicable in many different situations. Design patterns can speed up the development process by leveraging tested and proven development practices.

Design patterns categories

Design patterns are categorized into three main types: creational, structural, and behavioural patterns.

Creational patterns

Patterns in this category deal with creating instances from classes.

• Singleton – Ensures that the class has only one instance and provides that as an access point.
• Builder – Allows the construction of a complex object to be broken down into a series of simple steps.
• Prototype – Creates an instance of a new object by cloning an existing one.
• Factory – Provides an interface for creating objects of derived classes.
• Abstract factory – Provides an interface for creating families of related objects without specifying their concrete classes.

Structural patterns

Patterns in this category deal with class structure such as inheritance and composition.

• Adapter – Allows objects with incompatible interfaces to collaborate.
• Bridge – Separates an abstraction from its implementation so that both can vary independently.
• Composite – Allows objects to be composed into tree structures and treated as individual objects.
• Decorator – Dynamically adds or removes responsibilities from objects without affecting others of the same class.
• Facade – Provides a simplified interface to a complex system.
• Flyweight – Allows sharing parts of existing objects to reduce the number of created objects.
• Proxy – Acts as a surrogate to control access to the original object.

Behavioural patterns

Patterns in this category deal with communication between objects.

• Chain of responsibility – Provides a way of passing a request between a chain of objects, where the currently addressed object has the ability to process it or send it on to the next object in the chain.
• Command – Implements the request–response model by wrapping a command and its metadata in an object.
• Iterator – Allows you to navigate through the items in a collection without revealing their base type.
• Mediator – Provides centralized communication between different objects in the system.
• Memento – Allows you to save and subsequently restore the previous state of the object.
• Observer – Provides a mechanism for notifying all interested objects when a change occurs to the observed object.
• State – Allows an object to alter its behaviour when its internal state changes.
• Strategy – Defines a family of interchangeable algorithms, encapsulating each in a separate class.

About the author

Jozef Wagner

Java Developer Senior

Viac ako 10 rokov programujem v Jave, momentálne pracujem v msg life Slovakia ako Java programátor senior a pomáham zákazníkom implementovať ich požiadavky do poistného softvéru Life Factory. Vo voľnom čase si rád oddýchnem v lese, prípadne si zahrám nejakú dobrú počítačovú hru.