Decorator design pattern in Java

-

 

The intent of the Decorator Design Pattern is to attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to sub-classing for extending functionality. The Decorator Pattern is used to extend the functionality of an object dynamically without having to change the original class source or using inheritance. This is accomplished by creating an object wrapper referred to as a Decorator around the actual object. The Decorator object is designed to ave the same interface as the underlying object. This allows a client object to interact with the Decorator object in exactly the same manner as it would with the underlying ctual object. The Decorator object contains a reference to the actual object. The Decorator object receives all requests (calls) from a client. In turn, it forwards these calls to the underlying object. The Decorator object adds some additional functionality before or after forwarding requests to the underlying object. This ensures that the additional functionality can be added to a given object externally at runtime without modifying its structure. We use inheritance or composition to extend the behavior of an object but this is done at compile time and it’s applicable to all the instances of the class. We can’t add any new functionality of remove any existing behavior at runtime – this is when Decorator pattern comes into picture.

When to use the Decorator Design Pattern:

Use the Decorator pattern in the following cases:

  • To add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects.
  • For responsibilities that can be withdrawn.
  • When extension by sub-classing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for sub-classing.
  • It’s easy to maintain and extend when the number of choices are more.

Usage in Java:

  • Decorator pattern is used a lot in Java IO classes, such as FileReader, BufferedReader etc.
  • The disadvantage of decorator pattern is that it uses a lot of similar kind of objects (decorators).

Decorator UML class diagram


Source Decorator pattern - Wikipedia


Real-World Example




Go to source code

Comments

Post a Comment

Popular posts from this blog

Debug Java Stream in Intellij Idea

-
Image
Stream is a very powerful feature. it allows you to take full advantage of modern multi-core architectures and lets you process data in a declarative way.  Unfortunately stream API may sometimes be difficult to debug. This happens because they require you to insert additional breakpoints and thoroughly analyze each transformation inside the stream.  IntelliJ IDEA provides a solution to this by letting you visualize what is going on in Java Stream operations. Just install plugin called “Java Stream Debugger”. Once you have enabled this plugin you can simply debug your code. This plugin will bring a trace icon (Trace Current Stream Chain button).   Trace Current Stream Chain button Once you click on that icon you get the visualization of your stream pipeline.  For every stream operation, we have got a dedicated tab. you have to switch to the relevant tab to understand what it is doing. 
Read more

Creating Efficient Docker Images with Spring Boot 2.3

-
Image
Spring Boot 2.3 brings with it some interesting new features that can help you package up your Spring Boot application into Docker images. The first problem with common docker techniques is that the jar file is not unpacked. There’s always a certain amount of overhead when running a fat jar, and in a containerized environment this can be noticeable. It’s generally best to unpack your jar and run in an exploded form. The second issue with the file is that it isn’t very efficient if you frequently update your application. Docker images are built in layers, and in this case your application and all its dependencies are put into a single layer. Since you probably recompile your code more often than you upgrade the version of Spring Boot you use, it’s often better to separate things a bit more. If you put jar files in the layer before your application classes, Docker often only needs to change the very bottom layer and can pick others up from its cache. Two new features are introduced in Sp...
Read more

CRUD Goes Even Easier With JPABuddy

-
Image
Create, Read, Update and Delete are the four basic operations of persistence storage. We can say these operations collectively as an acronym CRUD. These operations can be implemented in JPA. JPA is a standard for ORM. It is an API layer that maps Java objects to the database tables.  ORM stands for Object Relational Mapping. It converts data between incompatible type systems in object-oriented programming languages.  JPA Buddy is an IntelliJ IDEA plugin that helps developers work efficiently. JPA Buddy is a tool that is supposed to become your faithful coding assistant for projects with JPA and everything related. It is an advanced plugin for IntelliJ IDEA intended to simplify and accelerate everything related to JPA and surrounding mainstream technology. In fact, you can develop an entire CRUD application or a simple microservice by spending nearly zero time writing boilerplate code. The video demonstrates the features of JPA Buddy by creating a simple CRUD application from ...
Read more