Command Design Pattern Tutorial with Java Code Example for Beginners

Veröffentlicht am: 19 Januar 2023
auf dem Kanal: codeonedigest

325

Command is a behavioral design pattern that turns a request into a stand-alone object that contains all information about the request. This transformation lets you pass requests as a method arguments, delay or queue a request’s execution, and support undoable operations.

The Command pattern is used to create objects that represent actions and events in an application. A command object encapsulates an action (event) and contains all information required to understand exactly what has happened. The Command pattern forwards requests along a chain of classes, but the Command pattern forwards a request only to a specific module. It encloses a request for a specific action inside an object and gives it a known public interface.

When you build a Java user interface, you provide menu items, buttons, and checkboxes and so forth to allow the user to tell the program what to do. When a user selects one of these controls, the program receives an ActionEvent, which it must trap by subclassing, the actionPerformed event. Command pattern allows a request to exist as an object.

The Command pattern suggests that GUI objects shouldn’t send these requests directly. Instead, you should extract all of the request details, such as the object being called, the name of the method and the list of arguments into a separate command class with a single method that triggers this request.

Command objects serve as links between various GUI and business logic objects. From now on, the GUI object doesn’t need to know what business logic object will receive the request and how it’ll be processed. The GUI object just triggers the command, which handles all the details.

** Where to use Command Design Pattern **
1. Where you want an action that can be represented in many ways, like dropdown menu, buttons and popup menu.
2. To create undo/redo functionality by reusing the code and command object.

** Advantages of Command Design Pattern **
1. A command object is a possible storage for procedure parameters. It can be used while assembling the parameters for a function call and allows the command to be set aside for later use.
2. A class is a suitable place to collect code and data related to a specific action or event.
3. It allows the reaction to a command to be executed some time after it has occurred.
4. Command objects enable data structures containing multiple commands.
5. Command objects support undoable operations, provided that the command objects are stored (for example in a linked list).

** Chapter Timestamps **
0:00 Welcome to Command Design Pattern
0:28 Recap of Chain of Responsibility Design Pattern
1:41 Introduction of Command Design Pattern
3:17 Example of Command Design Pattern
7:57 Java code example of Command Design Pattern
11:23 Where to use Command Design Pattern
11:50 Advantages of Command Design Pattern
12:35 Summary of Command Design Pattern
13:10 Next video on State Design Pattern

#commandpattern #commanddesignpattern #javadesignpatterns

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