Adapter Design Pattern in Java with Example

Adapter design pattern in Java, also known as the Wrapper pattern is another very useful GOF pattern, which helps to bridge the gap between two classes in Java. As per the list of Gang of Four patterns, Adapter is a structural pattern, much like Proxy, Flyweight, Facade, and Decorator pattern in Java. As the name suggest, Adapter allows two classes of a different interface to work together, without changing any code on either side. You can view Adapter pattern is a central piece of the puzzle, which joins two pieces, which can not be directly joined because of different interfaces. I see a couple of reference of Adapter design pattern in one of my favorite book Clean Code, but the idea is very well explained in Head First Design Pattern, the image which they show to illustrate Adapter design pattern is worth all the talk.

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Java Object Oriented Analysis and Design Problem - Vending Machine Part 2

This is the second part of Java tutorial to show how to create Vending Machine in Java. In the first part, we have discussed problem statement and the solution itself, but unit testing and design document was still pending, which we'll see in this article.  As I said, there are multiple ways to implement Vending machine in Java e.g. you could have easily used state design pattern to implement a vending machine, in fact, it's one of the best examples of State design pattern. Vending machine behaves differently on different states e.g. return a product if the machine is not empty, otherwise, it just returns coins, so it ideally fits in state design pattern. Though, In our solution, I have not used the state design pattern but have just coded the solution with an if else block. This is easier because of a limited number of state and not many state transition but in more real world scenario, state design pattern is better as it uses Polymorphism and removes the logic we have put inside the if-else block.

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Design a Vending Machine in Java - Interview Question

How do you design a Vending Machine in Java? is one of the good Java interview questions mostly asked at Senior level Java developer Interviews. In a typical coding interview, you will be given a problem statement to develop a vending machine and within a limited time, usually, 2 to 3 hours you need to produce design document, working code and unit test in Java. One of the key advantages of such Java interviews is that you can test many essential skills or a candidate in one go. In order to complete  the design, coding, and unit testing of  a Vending machine, a candidate needs to be really good in all three departments. By the way, this kind of real world problem is also a good exercise to improve your object-oriented analysis and design skills (see here), which is very important if you want to become a good application developer.

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Command design Pattern in Java with Example

In simple words, Command design pattern is used to separate a request for an action from the object which actually performs the action. This decoupling between Invoker and Receiver object provides a uniform ways to perform different types of actions. This decoupling is achieved using a Command object, which is usually an interface with methods like execute(). The Requestor or Invoker only knows about Command object, and doesn't care of the actual object which process the request, which can be different. This transparency leads clean code on Invoker side and also enables opportunity to do several smart things on Command side. Your Command object can be as dumb as simply delegating request to Receiver and can be as smart as recording last command for performing UNDO and REDO functionality.

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Data Access Object (DAO) design pattern in Java - Tutorial Example

Data Access Object or DAO design pattern is a popular design pattern to implement persistence layer of Java application. DAO pattern is based on abstraction and encapsulation design principles and shields rest of application from any change in the persistence layer e.g. change of database from Oracle to MySQL, change of persistence technology e.g. from File System to Database. For example, if you are authenticating the user using a relational database and later your company wants to use LDAP to perform authentication. If you are using DAO design pattern to access database, it would be relatively safe as you only need to make a change on Data Access Layer. DAO design pattern also keeps coupling low between different parts of an application. By using DAO design pattern your View Layer is completely independent of DAO layer and only Service layer has the dependency on it which is also abstracted by using DAO interface.

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