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In graphical user interfaces (GUIs) or interactive console menus, user interactions such as clicking a menu item or pressing a shortcut must trigger specific business actions (such as opening a file, saving changes, or printing a document).
Hardcoding receiver logic directly inside UI menu components tightly couples the user interface to domain actions. If you tie menu items directly to specific classes, reusing actions across different UI triggers (like toolbar icons, context menus, or keyboard shortcuts) becomes difficult and error-prone.
Architecture of the Command Pattern Solution
The Command Design Pattern solves this tight coupling by turning user requests into standalone objects. In this menu implementation, the system is structured around four core participants:
-
Command Interface: Declares an execution method (typically
execute()) common to all menu commands. -
Concrete Commands: Encapsulate a binding between an action and a receiver. When
execute()is called, the command invokes the appropriate method on the receiver object. - Invoker (Menu / MenuItem): Holds a reference to a command and triggers it when a user action occurs, remaining completely agnostic of the receiver's underlying logic.
- Receiver: Contains the actual business logic to perform the requested operation (such as document editing, file storage, or rendering).
Key Architectural Benefits
Applying the Command pattern to menu systems provides distinct design advantages:
- Decoupled Invoker and Receiver: The menu component only knows how to execute a command, without depending directly on concrete receiver classes.
- Open/Closed Principle: Add new menu items and custom actions by introducing new command classes without altering existing menu code.
- Reusable Actions: Bind the same command instance to multiple UI controls (such as a top-level menu bar, a right-click context menu, and a keyboard shortcut).
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| Command Design pattern - Implementation [Menu] |
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| Command Design pattern - Implementation [Menu] |
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| Command Design pattern - Implementation [Menu] - Class Diagram |
/*
* Receiver
*/
public class WordDocument
{
public void open()
{
System.out.println("Document Opened");
}
public void save()
{
System.out.println("Document Saved");
}
public void close()
{
System.out.println("Document Closed");
}
}
Command.java
public interface Command
{
public void execute();
}
OpenCommand.java
public class OpenCommand implements Command
{
private WordDocument wordDocument;
public OpenCommand( WordDocument wordDocument )
{
this.wordDocument = wordDocument;
}
@Override
public void execute()
{
wordDocument.open();
}
}
SaveCommand.java
public class SaveCommand implements Command
{
private WordDocument wordDocument;
public SaveCommand( WordDocument wordDocument )
{
this.wordDocument = wordDocument;
}
@Override
public void execute()
{
wordDocument.save();
}
}
CloseCommand.java
public class CloseCommand implements Command
{
private WordDocument wordDocument;
public CloseCommand( WordDocument wordDocument )
{
this.wordDocument = wordDocument;
}
@Override
public void execute()
{
wordDocument.close();
}
}
MenuOptions.java
/*
* Invoker
*/
public class MenuOptions
{
private Command openCommand;
private Command saveCommand;
private Command closeCommand;
public MenuOptions( Command open, Command save, Command close )
{
this.openCommand = open;
this.saveCommand = save;
this.closeCommand = close;
}
public void clickOpen()
{
openCommand.execute();
}
public void clickSave()
{
saveCommand.execute();
}
public void clickClose()
{
closeCommand.execute();
}
}
Client.java
public class Client
{
public static void main( String[] args )
{
WordDocument wordDocument = new WordDocument();
Command openCommand = new OpenCommand(wordDocument);
Command saveCommand = new SaveCommand(wordDocument);
Command closeCommand = new CloseCommand(wordDocument);
MenuOptions menu = new MenuOptions(openCommand, saveCommand, closeCommand);
menu.clickOpen();
menu.clickSave();
menu.clickClose();
}
}
Output
Document Opened
Document Saved
Document Closed
