Java is a most popular, robust, secure, platform independent and multithreading based high level programming language, because of this it is preferably used by many programmers.
4. It's a good idea to save the project, because that will allow you to
change the project in case you decide to do something different
with future sliders.
There are many Java programming course tutorials that you will
find to learn design patterns, but not really talked about a
particular design pattern in depth.
So today we learn one of the important design patterns, which is
often overlooked by Java developers.
Yes, I'm talking about the command pattern that can help you
write flexible, loosely coupled code to implement actions and
events in your application.
In simple terms, the command design pattern is used to separate
a request for an action from the object that actually performs the
action.
This decoupling between Invoker and Receiver object provides a
5. The Requestor or Invoker only knows Command object and does not care
about the actual object that processes the request, which may be different. This
transparency leads to cleaner code on the Invoker page and also allows the
ability to do several intelligent things on the command page.
Your command object can be so stupid, how the request delegate to the
recipient and can be as smart as the record of the last command for
implementing UNDO and Redo functionality.
6. The command pattern ensures that your code with the open closed design
principle, the O of SOLID design principles, compliant, which means that
adding a new command would be very easy to create a new implementation of
the Command interface and the Invoker code is not affected.
https://www.exltech.in/java-training.html
The Command pattern is popular in GUI applications, where we use a lot of
commands, e.g. Open, Close, Save, cut, Copy, Paste, and appropriate UNDO
and REDO operations. You can also see the Java Design Patterns Masterclass,
which not only covers command patterns and has recently been updated to Java
SE 8.
7. 1. Command Pattern-Terminology
Before proceeding and implementing a command pattern in Java, we will
familiarize ourselves with the terminology used in this pattern.
Client-creates concrete command object and configure with recipient
Invoker-Who hold command, and calls execute () method on the Command
object
Recipient-actual object that processes the request
Command-Interface that handles the request from the Invoker and delegates it
to the recipient
ConcreteCommand - implementation of the command interface for a specific
task
UML diagram of the command Design Pattern
Here is the UML diagram of the command design pattern, that makes things
clearer.
8. You can see that the Client has a reference to a callback interface that has a
generic method execute(). The individual commands implement this interface
and provide an implementation, which is nothing else than delegating to the
actual object.
The most important thing is that the client does not know about the actual
object that performs an action on behalf of these commands. This decoupling
leads to flexible code and makes it easy to add new commands without
affecting the client code.
Command design pattern in Java-example
Here is our sample program to demonstrate how to use the command pattern
in Java.
9. This Java Certification course exams, formerly known as Sun Java
Certification exams, are industry-recognized certifications in Java technology.
It focuses on key roles in software application development and enterprise
architecture. Each certification is central to the learning process as it provides
validation of skill sets for specific job roles.
This class represents a Client of the command pattern
Client.Java
import java.util.HashMap;
import java.util.Map;
import org.slf4j.Logger;
import org.slf4j.Logger factory;
10. /**
* Java program to implement command design patterns with example.
*
* @author Paul Javin
*/
public class Client {
private static final Logger logger = LoggerFactory.getLogger (Client.Class);
public static void main (String args[]) {
// Client creates the Invoker object, command object and configure it
Menu menu = new menu();
Menu.setCommand ("Create", new CreateCommand());
Menu.setCommand ("Delete", new DeleteCommand());
11. This class represents a command
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