Command Pattern

Command: deklariert eine Schnittstelle zum Ausführen einer Methode. Concrete Command: Erbt von Command und implementiert .execute(). Verpackt eine Funktion, die eigene Logik enthalten kann und/oder etwas der Receiver Klasse ausführt. Client: die Anwendung (Main) Invoker: Verwaltet die Concrete Commands. Hier können .undo() usw. implementiert werden Receiver: Jede Klasse kann ein Receiver sein. Hier werden die Receiver Methoden von einem Concrete Command verpackt

Beispiel

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Command

public interface Command{
	public void execute();
}

Receiver

public class Receiver{
	public void doSomething(String state){
		System.out.println("State: " + state);
	}
}

Concrete Command

public class ConcreteCommand implements Command{
	private Receiver receiver;
	private String state;
	
	public ConcreteCommand(Receiver receiver){
		this.receiver = receiver;
	}
	
	@Override
	public void execute(){
		receiver.doSomething(state);
	}
	
	public void setState(String state){
		this.state = state;
	}
}

Invoker

public class Invoker{
	private Command command;
	
	public void setCommand(Command command){
		this.command = command;
	}
	
	public void executeCommand(){
		command.execute();
	}
}

Client (Main)

public class Main{
	public static void main(String[] args){
		Receiver receiver = new Receiver();
		String state1 = "STATE_ON";
		String state2 = "STATE_OFF";
		
		ConcreteCommand concreteCommand1 = new ConcreteCommand(receiver);
		concreteCommand1.setState(state1);
		
		ConcreteCommand concreteCommand2 = new ConcreteCommand(receiver);
		concreteCommand2.setState(State2);
		
		Invoker invoker1 = new Invoker();
		invoker1.setCommand(concreteCommand1);
		Invoker invoker2 = new Invoker();
		invoker2.setCommand(concreteCommand2);
		
		invoker1.executeCommand(); // Output: State: STATE_ON
		invoker2.executeCommand(); // Output: State: State_OFF
	}
}