{"id":44821,"date":"2015-09-30T06:45:01","date_gmt":"2015-09-30T03:45:01","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=44821"},"modified":"2023-12-07T13:09:40","modified_gmt":"2023-12-07T11:09:40","slug":"command-design-pattern","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2015\/09\/command-design-pattern.html","title":{"rendered":"Command Design Pattern Example"},"content":{"rendered":"

This article is part of our Academy Course titled Java Design Patterns<\/a>.<\/em><\/p>\n

In this course you will delve into a vast number of Design Patterns and see how those are implemented and utilized in Java. You will understand the reasons why patterns are so important and learn when and how to apply each one of them. Check it out here<\/a>!<\/p>\n

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Table Of Contents<\/h4>\n
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1. Introduction<\/a><\/dt>\n
2. What is the Command Design Pattern<\/a><\/dt>\n
3. Implementing the Command Design Pattern<\/a><\/dt>\n
4. When to use the Command Design Pattern<\/a><\/dt>\n
5. Command Design Pattern in JDK<\/a><\/dt>\n
6. Download the Source Code<\/a><\/dt>\n<\/dl>\n<\/div>\n

<\/a>1. Introduction<\/h2>\n

The Command Design Pattern is a behavioral design pattern and helps to decouples the invoker from the receiver of a request.<\/p>\n

To understand the Command Design Pattern let’s create an example to execute different types of jobs. A job can be anything in a system, for example, sending emails, SMS, logging, and performing some IO functions.<\/p>\n

The Command pattern would help to decouple the invoker from a receiver and helps to execute any type of job without knowing its implementation. Let us make this example more interesting by creating threads which will help to execute these jobs concurrently. As these jobs are independent of each other, so the sequence of execution of these jobs is not really important. We will create a thread pool to limit the number of threads to execute jobs. A command object will encapsulates jobs and will hand it over to a thread from the pool that will execute the job.<\/p>\n

Before implementing the example, let\u2019s know more about the Command Design Pattern.<\/p>\n

<\/a>2. What is the Command Design Pattern<\/h2>\n

The intent of the Command Design Pattern is to encapsulate a request as an object, thereby letting the developer to parameterize clients with different requests, queue or log requests, and support undoable operations.<\/p>\n

In general, an object-oriented application consists of a set of interacting objects each offering limited, focused functionality. In response to user interaction, the application carries out some kind of processing. For this purpose, the application makes use of the services of different objects for the processing requirement.<\/p>\n

In terms of implementation, the application may depend on a designated object that invokes methods on these objects by passing the required data as arguments. This designated object can be referred to as an invoker as it invokes operations on different objects. The invoker may be treated as part of the client application. The set of objects that actually contain the implementation to offer the services required for the request processing can be referred to as Receiver<\/code> objects.<\/p>\n

Using the Command pattern, the invoker that issues a request on behalf of the client and the set of service-rendering Receiver<\/code> objects can be decoupled. The Command pattern suggests creating an abstraction for the processing to be carried out or the action to be taken in response to client requests. This abstraction can be designed to declare a common interface to be implemented by different concrete implementers referred to as Command<\/code> objects. Each Command<\/code> object represents a different type of client request and the corresponding processing.<\/p>\n

A given Command<\/code> object is responsible for offering the functionality required to process the request it represents, but it does not contain the actual implementation of the functionality. Command<\/code> objects make use of Receiver<\/code> objects in offering this functionality.<\/p>\n

\"Figure<\/a>
Figure 1 – Command pattern Class diagram<\/figcaption><\/figure><\/p>\n

Command<\/strong><\/p>\n