Category Archives: Design Patterns

Design Patterns – Factory Pattern – Part III

In this article, we will see how to use a factory pattern. Factory pattern is a creational type of design pattern, in short it provides a way to create objects. Another important point to note about this design pattern is that client who uses factory pattern is not aware of the implementation of factory pattern.

Even in our previous post Spring Boot REST CRUD API, we have used factory pattern to implement managers at service level. As part of this post, we will show another example of factory pattern. Factory pattern mainly used in cases when client just needs a class/object that can handle the job of doing the work at runtime without knowing any details of how it was implemented.

To show how to implement factory pattern, let’s assume we have different types of vehicles and we want to know what their maximum speed is.

Create an interface –

Our interface of vehicle will have a method to return a max speed of vehicle.

package com.betterjavacode.designpatterns.factoryexample;

public interface Vehicle {

void speed();


Now, we will have different classes (car, truck,bus,motorcycle) that will implement this interface to return their maximum speed. For article purposes, we will only be showing one class.

package com.betterjavacode.designpatterns.factoryexample;

public class Car implements Vehicle {

 public void speed() 

   System.out.println("Max Speed of this car is 100 mph");


To get an instance of an object, we will create a factory class that will return me appropriate instance of vehicle object based on what vehicle type I pass.

package com.betterjavacode.designpatterns.factoryexample;

public class VehicleFactory {

public Vehicle getVehicle(String vehicleType)
   if (vehicleType == null) 
      return null;
   if (vehicleType.equalsIgnoreCase("car")) {
     return new Car();
   if (vehicleType.equalsIgnoreCase("bus")) {
     return new Bus();
   if (vehicleType.equalsIgnoreCase("motorcycle")) 
     return new Motorcycle();
   if ( vehicleType.equalsIgnoreCase("truck")) 
     return new Truck();
    return null;


A factory pattern demo class will get any of object of type vehicle at runtime.

package com.betterjavacode.designpatterns;

import com.betterjavacode.designpatterns.factoryexample.Vehicle;
import com.betterjavacode.designpatterns.factoryexample.VehicleFactory;

public class FactoryPatternDemo {

public static void getSpeed(String vehicleType) {
 VehicleFactory vehicleFactory = new VehicleFactory();

Vehicle veh1 = vehicleFactory.getVehicle(vehicleType);



In this example, we have shown how to implement a design pattern type factory pattern. The code for this is available design patterns.


  1. Factory Pattern Example
  2. Factory Pattern

Design Patterns – Singleton Pattern – Part II

In this post, we will discuss Singleton Pattern which is of Creational type design pattern. You can checkout the introductory post about design patterns here.

Singleton Design Pattern

Singleton design pattern is the simplest design patterns in software engineering. As Singleton is a creational type of design pattern, it is used to create an object.

In this design pattern, a single class creates an object , but also makes sure that only a single object is created. This class provides a way to access the object, so to avoid the need to instantiate the object.


In this design pattern a class will have a private constructor and a static method to provide access to static member of the class instance. Most of the time singleton pattern is used in logger and configuration classes implementation.

package com.betterjavacode.designpatterns;

public class SingletonDemo {

private static SingletonDemo demo;

private SingletonDemo()



public static SingletonDemo getInstance()

if (demo == null)
demo = new SingletonDemo();

return demo;

public void printSingletonDemo()

System.out.println(" This is a singleton design pattern demo ");


Now any client code who wants to use SingletonDemo class, can do this with SingletonDemo.getInstance(). Major advantage of Singleton design pattern is it allows only one instance of object is created.


Code for this post is available to download design patterns.

Design Patterns in Java – Introduction

In coming next few posts, we will build a series of posts to discuss design patterns in Java. In this introductory post, we will give a brief idea about design patterns.

What are design patterns?

Design patterns are programming strategies independent of programming language to build a solution for common object-oriented programming problems. One of the major benefits of design patterns is that the most code is reusable and easily maintainable.

Example of design pattern in real world?

To understand what exactly design patterns are, let’s consider a real life example. Suppose we have an animal class. All the subclasses for animals like Elephant, Dog, Cat can be built by using methods to make these objects.

An abstract factory is a design pattern, that can be used in this example.

abstract class AbstractAnimalFactory


public Elephant makeElephant() {

return new Elephant();


public Dog makeDog(){

return new Dog();




abstract class Animal{



class Elephant extends Animal{



class Dog extends Animal{




Types of design patterns

Based on their purpose, design patterns are divided into three types of patterns creational, structural and behavioral. Further, each of these design patterns have sub-types.

Creational Design Pattern

  1. Singleton Design Pattern
  2. Factory Pattern
  3. Absolute factory Pattern
  4. Builder Pattern
  5. Prototype Pattern

Structural Design Pattern

  1. Adapter Pattern
  2. Composite Pattern
  3. Proxy Pattern
  4. Flyweight Pattern
  5. Facade Pattern
  6. Bridge Pattern
  7. Decorator Pattern

Behavioral Design Pattern

  1. Template Method Pattern
  2. Mediator Pattern
  3. Chain of responsibility Pattern
  4. Observer Pattern
  5. Strategy Pattern
  6. Command Pattern
  7. State Pattern
  8. Visitor Pattern
  9. Interpreter Pattern
  10. Iterator Pattern
  11. Memento Pattern

In coming posts, we will discuss each design pattern with a production-ready example.

Advantages of design patterns

  1. Reusable in multiple projects
  2. Capture the complete experience of software engineering
  3. Provide clarity to system architecture


In this post, we discussed a simple introduction to design patterns. In coming posts, we will build actual design patterns to show how design patterns work.


  1. Design patterns in Java
  2. Design Patterns Brief Introduction