· The Command Pattern encapsulates a request as an object, allowing for the separation of sender and receiver.
· Commands can be parameterized, meaning you can create different commands with different parameters without changing the invoker(responsible for initiating command execution).
· It decouples the sender (client or invoker) from the receiver (object performing the operation), providing flexibility and extensibility.
· The pattern supports undoable(action or a series of actions that can be reversed or undone in a system) operations by storing the state or reverse commands.
class Light {
private boolean switchedOn = false;
public void switchLights() {
switchedOn = !switchedOn;
System.out.println("Light is now " + (switchedOn ? "ON" : "OFF"));
}
public boolean isSwitchedOn() {
return switchedOn;
}
}
interface Command {
void turnOn();
void turnOff();
}
class LightCommand implements Command {
private Light light;
public LightCommand(Light light) {
this.light = light;
}
public void turnOn() {
if (!light.isSwitchedOn()) {
light.switchLights();
} else {
System.out.println("Light is already ON");
}
}
public void turnOff() {
if (light.isSwitchedOn()) {
light.switchLights();
} else {
System.out.println("Light is already OFF");
}
}
}
class RemoteControl {
private Command command;
public RemoteControl(Command command) {
this.command = command;
}
public void pressOnButton() {
command.turnOn();
}
public void pressOffButton() {
command.turnOff();
}
}
public class CommandPattern {
public static void main(String[] args) {
Light light = new Light();
Command lightCommand = new LightCommand(light);
RemoteControl remoteControl = new RemoteControl(lightCommand);
remoteControl.pressOnButton(); // Light is now ON
remoteControl.pressOffButton(); // Light is now OFF
remoteControl.pressOffButton(); // Light is already OFF
remoteControl.pressOnButton(); // Light is now ON
}
}
@startuml
skinparam handwritten true
skinparam shadowing false
interface Command {
+ turnOn(): void
+ turnOff(): void
}
class Light {
- switchedOn: boolean
+ switchLights(): void
+ isSwitchedOn(): boolean
}
class LightCommand {
- light: Light
+ LightCommand(light: Light)
+ turnOn(): void
+ turnOff(): void
}
class RemoteControl {
- command: Command
+ RemoteControl(command: Command)
+ pressOnButton(): void
+ pressOffButton(): void
}
class CommandPatternDemo {
+ main(args: String[]): void {static}
}
' Relationships'
Command <|.. LightCommand : implements
LightCommand o-- Light : "1" has "1"
RemoteControl o-- Command : "1" has "1"
CommandPatternDemo ..> Light : uses
CommandPatternDemo ..> LightCommand : uses
CommandPatternDemo ..> RemoteControl : uses
@enduml
