Java Design Patterns - Examples

Design patterns are reusable solutions to commonly occurring problems in software design. They are proven solutions that can help to simplify and streamline software development, and they are used extensively in software engineering.

Design patterns are typically classified into three categories:

  • Creational Patterns : These patterns are used to create objects and classes. They help to create objects in a way that is flexible, efficient, and reusable. Examples of creational patterns include the Singleton pattern, Factory pattern, and Abstract Factory pattern.
  • Structural Patterns : These patterns are used to form complex objects and classes from simpler objects and classes. They help to create objects and classes that are easy to maintain, extend, and modify. Examples of structural patterns include the Adapter pattern, Bridge pattern, and Facade pattern.
  • Behavioral Patterns : These patterns are used to manage communication and coordination between objects and classes. They help to create objects and classes that are flexible, extensible, and easy to modify. Examples of behavioral patterns include the Observer pattern, Command pattern, and Strategy pattern.

Design patterns are typically documented using a common format, which includes the problem that the pattern addresses, the solution that it provides, and the consequences of using the pattern. They are implemented using object-oriented programming techniques, and are typically implemented using programming languages like Java, C++, and Python.

Using design patterns can help to improve the quality, maintainability, and extensibility

Table of Content :

#1. Creational design patterns :

Creational design patterns are a category of design patterns that focus on the creation of objects and classes. These patterns help to create objects in a way that is flexible, efficient, and reusable. There are several types of creational design patterns, including:

  • 1. Singleton Pattern : This pattern ensures that only one instance of a class is created and provides a global point of access to it. Read more about the Singleton design pattern in Java

  • 2. Factory Pattern: This pattern provides a way to create objects without exposing the instantiation logic to the client. It separates the object creation logic from the client code. Read more about the Factory design pattern in Java

  • 3. Abstract Factory Pattern : This pattern provides an interface for creating related or dependent objects without specifying their concrete classes.

  • 4. Builder Pattern: This pattern separates the construction of a complex object from its representation, allowing the same construction process to create different representations.

  • 5. Prototype Pattern : This pattern creates new objects by cloning an existing object rather than creating a new one from scratch.

  • 5. Object Pool Pattern : This pattern manages a pool of objects that can be reused to improve performance and reduce memory usage.

Overall, creational design patterns help to create objects and classes in a way that is flexible, efficient, and reusable. They provide a set of proven solutions to common problems in software design and are used extensively in software engineering

#2 Structural design patterns :

Structural design patterns are a category of design patterns that focus on the composition of objects and classes to form larger structures or systems. These patterns help to create objects and classes that are easy to maintain, extend, and modify. There are several types of structural design patterns, including:

  • Adapter Pattern : This pattern adapts the interface of a class to another interface that the client expects. It allows incompatible interfaces to work together.

  • Bridge Pattern: This pattern separates an object's abstraction from its implementation, allowing both to be modified independently.

  • Composite Pattern: This pattern allows you to compose objects into a tree-like structure to represent part-whole hierarchies. It treats individual objects and compositions of objects uniformly

  • Decorator Pattern: This pattern adds behavior or responsibilities to an object dynamically, without changing its interface.

  • Facade Pattern: This pattern provides a simplified interface to a complex system, hiding its complexities from clients.

  • Flyweight Pattern: This pattern shares objects to reduce memory usage, creating a pool of objects that can be reused.

  • Proxy Pattern: This pattern provides a surrogate or placeholder for another object to control access to it

Overall, structural design patterns help to create objects and classes that are easy to maintain, extend, and modify by composing them into larger structures or systems. They provide a set of proven solutions to common problems in software design and are used extensively in software engineering.

#3 Behavioral design patterns:

Behavioral design patterns are a category of design patterns that focus on the communication and interaction between objects and classes. These patterns help to create objects and classes that are flexible, extensible, and easy to modify. There are several types of behavioral design patterns, including:

  • Template Method Pattern: The Template Method Pattern is a behavioral design pattern that defines the skeleton of an algorithm in a method, allowing subclasses to modify certain steps of the algorithm without changing its structure. The idea behind this pattern is to define the steps of an algorithm in a base class, while allowing subclasses to override or extend certain steps to implement specific behaviors.
  • Mediator Pattern: The Mediator Pattern is a behavioral design pattern that promotes loose coupling between objects by allowing them to communicate through a mediator object, instead of directly with each other. The mediator object acts as a central hub that receives messages from objects and relays them to other objects, as necessary. This reduces the dependencies between objects and makes the system more modular and extensible.

  • Chain of Responsibility Pattern: The Chain of Responsibility Pattern is a behavioral design pattern that allows a set of objects to handle a request or a task in a sequential order. Each object in the chain has the ability to handle the request or pass it on to the next object in the chain. This way, the request travels through the chain until it is handled by one of the objects in the chain.
    The Chain of Responsibility Pattern involves the following participants:
    Handler: Defines an interface for handling requests and maintains a reference to the next handler in the chain.
    Concrete Handler: Implements the Handler interface and handles requests that it is capable of handling. If it cannot handle a request, it passes it on to the next handler in the chain.
    Client: Sends requests to the first object in the chain.

  • Observer Pattern: The Observer Pattern is a behavioral design pattern that defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. The Observer Pattern involves the following participants:
    Subject: Maintains a list of observers, provides an interface for attaching and detaching observers, and notifies its observers when its state changes.
    Observer: Defines an interface for receiving updates from the subject.
    Concrete Subject: Implements the Subject interface and maintains the state of interest.
    Concrete Observer: Implements the Observer interface and stores a reference to the Concrete Subject object.

  • Strategy Pattern : The Strategy Pattern is a behavioral design pattern that enables an object to select and use a specific algorithm from a family of algorithms at runtime. The Strategy Pattern involves the following participants:.
    • Context: Defines an interface that is used by clients to access its services. The Context maintains a reference to a Strategy object and delegates the work to the Strategy object.
    • Strategy: Defines an interface that all concrete strategies must implement.
    • Concrete Strategy: Implements the Strategy interface and provides a specific algorithm.
    Read more about the Strategy Design PatternDesign

  • Iterator Pattern The Iterator design pattern is a behavioral design pattern that provides a way to access the elements of a collection without exposing its internal structure. It separates the iteration over the collection from the collection itself, allowing the collection to change its internal structure without affecting the iteration. The Iterator pattern involves the following components:
    • Iterator Interface: This interface defines the methods for iterating over the elements of a collection. It typically includes methods such as hasNext(), next(), and remove().
    • Concrete Iterator: This is a concrete implementation of the Iterator interface that provides the actual implementation for the iteration methods based on the collection being iterated over.
    • Aggregate Interface: This interface defines the methods for creating an iterator object that can be used to iterate over the elements of a collection. It typically includes a method such as iterator().
    • Concrete Aggregate: This is a concrete implementation of the Aggregate interface that provides the actual implementation for the iterator() method. It returns a Concrete Iterator object that can be used to iterate over the elements of the collection
    Read more about the Iterator Design Pattern

In this article, we have seen the Java Design Patterns - Examples. All source code in the article can be found in the GitHub repository.