Design Patterns in Java

Design Patterns in Java

In this article, we will learn about the Design Patterns in Java, their advantages, and their categories. Design Patterns in Java are crucial for your software development and your Java interviews.

What are Java Design Patterns?

Design patterns in Java are reusable solutions or templates for commonly occurring problems in software design. These patterns provide a general framework for solving specific issues that arise during the software development life cycle.

By using design patterns in Java, developers can improve the quality of their code, make it easier to maintain and modify and make it more efficient and reusable. Design patterns have been extensively used in Java programming and are essential for every Java developer to understand.

Think of Design Patterns like a building with LEGO bricks. For example, you might have a set of instructions that show you how to build a car or a house using different LEGO pieces. Design patterns are like these instructions but for building software programs.

Why do we need Design Patterns in Java?

Some of the benefits of using Design Patterns during the Software Development Lifecycle are as follows:

  • They provide solutions to commonly occurring problems in software development. Design patterns have been developed and refined over many years, providing a proven approach to solving specific problems. Using design patterns allows developers to save time and avoid reinventing the wheel.
  • They promote code reuse and modularity. Design patterns encapsulate the code for specific functionality and make it easier to reuse that code in other parts of the application. This makes the code more modular, easier to maintain, and flexible.
  • They improve the quality of the code. Design patterns promote good coding practices and make the code more organized, easier to read and understand, and easier to test. Hence, it improves the overall quality of the code and makes it more maintainable and robust.
  • They help developers communicate more effectively. Design patterns provide a common language and understanding between developers. For example, when a developer says they are using the Singleton pattern, other developers will know exactly what they mean and how the code is structured.
  • They provide a framework for solving complex problems. Complex problems can be challenging, but design patterns offer a proven framework for tackling these problems. In addition, developers can solve difficult problems more effectively and efficiently by breaking them down complex problems into smaller, more manageable components.

Design Pattern Categories

Creational Design Patterns

Creational design patterns deal with creating objects. These patterns provide general solutions to problems that arise during the creation of objects, and they help to make object creation more flexible and efficient.

Creational design patterns aim to abstract the object creation process and make it more dynamic and reusable. They encapsulate the knowledge of which classes and objects are required to create a new instance and hide the complexity of creating them from the client code.

Creational Design patterns can also improve performance and save memory by reducing the number of objects that need to be created and managed.

Following are types of Creational Design Pattern

  • Singleton Design Pattern: This pattern ensures that a class has only one instance and provides a global point of access to it.
  • Factory Method Pattern: This pattern provides an interface for creating objects but allows subclasses to decide which class to instantiate. It decouples the client code from the actual implementation of the objects.
  • Abstract Factory Pattern: This pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes. It allows the client code to work with the abstract interface instead of the concrete classes.
  • Builder Pattern: This pattern separates the construction of a complex object from its representation, allowing the same construction process to create different models. It allows the client code to create complex objects step by step.
  • Prototype Pattern: This pattern allows the creation of new objects by cloning existing ones, avoiding the overhead of creating new objects from scratch. It provides a way to create objects with different initial states without creating subclasses or modifying the constructor.

Structural Design Patterns

Structural design patterns deal with the organization of classes and objects. These patterns provide ways to compose objects to form larger structures while keeping the individual objects and their relationships intact.

The primary goal of structural design patterns is to simplify the design of large systems by providing flexible mechanisms for object composition. These patterns allow developers to create complex structures by combining smaller and simpler objects in a way that is easy to understand and maintain.

Following are the types of Structural Design Patterns

  • Adapter Pattern: This pattern is used to convert the interface of a class into another interface that the client expects. It allows incompatible classes to work together by wrapping an object and exposing a different interface.
  • Bridge Pattern: The Bridge pattern decouples an abstraction from its implementation so that the two can vary independently. It allows the client code to work with different implementations of the same abstraction.
  • Composite Pattern: This pattern is used to represent part-whole hierarchies of objects. It allows the client code to treat individual objects or group objects uniformly.
  • Decorator Pattern: This pattern dynamically adds behavior or responsibilities to individual objects without affecting the behavior of other objects of the same class. It allows the client code to add or remove responsibilities at runtime.
  • Facade Pattern: This pattern provides a simplified interface to a complex system of classes. It hides the system’s complexity from the client code and allows the client code to work with a simple and unified interface.
  • Flyweight Pattern: This pattern is used to share objects that are expensive to create. It allows the client code to reuse existing objects instead of creating new ones, thus reducing memory usage and improving performance.

Behavioral Design Patterns

Behavioral design patterns deal with the interactions and responsibilities of objects. These patterns encapsulate and delegate behaviors among objects to achieve specific functionalities.

The primary goal of behavioral design patterns is to define how objects interact and provide a clear and understandable way to manage complex behaviors. These patterns help to simplify the design of large systems by providing flexible mechanisms for communication and delegation among objects.

Following are the types of Behaviour Design Patterns

  • Chain of Responsibility Pattern: This pattern creates a chain of objects that can handle requests in sequence. It allows the client code to send a request without knowing which object will handle it.
  • Command Pattern: This pattern encapsulates a request as an object, allowing the client code to parameterize different requests, queue or log requests, and support undoable operations.
  • Interpreter Pattern: This pattern defines the grammar of a language and provides an interpreter to evaluate sentences in the language. It allows the client code to define a domain-specific language and execute expressions in the language.
  • Iterator Pattern: This pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. It allows the client code to traverse a collection of objects without knowing its internal structure.
  • Mediator Pattern: This pattern defines an object that encapsulates the interactions between a set of objects, decoupling them from each other. It allows the client code to change the interactions between objects without changing their behavior.
  • Memento Pattern: This pattern allows an object to capture its internal state and restore it later. It allows the client code to save and restore the state of an object without exposing its implementation details.
  • Observer Pattern: This pattern defines a one-to-many dependency between objects so that all dependents are notified and updated automatically when one object changes state. It allows the client code to avoid tight coupling between objects and make them more reusable.
  • State Pattern: This pattern allows an object to change its behavior when its internal state changes. It allows the client code to treat different states of an object as separate classes and make them more extensible and maintainable.
  • Strategy Pattern: This pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It allows the client code to choose different algorithms at runtime without affecting the client code.
  • Template Method Pattern: This pattern defines the skeleton of an algorithm in a superclass, allowing its subclasses to override some steps of the algorithm without changing its overall structure. It allows the client code to reuse the common parts of an algorithm and customize the variable parts.
  • Visitor Pattern: This pattern separates an algorithm from the object structure it operates on by defining a new operation to be applied to the elements of the object structure. It allows the client code to add new operations to the object structure without changing its classes.


This article summarizes the concepts of Java Design Patterns and their advantages in the Software Development lifecycle. By understanding and using these common design patterns in Java, you can improve the quality and efficiency of your code and prepare for Java interviews.

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