abstract class Command {
  protected Receiver receiver;

  public Command(Receiver receiver) {
    this.receiver = receiver;
  }

  abstract public void execute();
}

public class ConcreteCommand extends Command {
  public ConcreteCommand(Receiver receiver) {
    super(receiver);
  }
  public void execute() {
    receiver.action();
  }
}

public class Receiver {
  public void action() {
    System.out.println("Receiver action()メソッド");
  }
}

public class Invoker {
  private Command command;

  public void setCommand(Command command) {
    this.command = command;
  }

  public void executeCommand() {
    command.execute();
  }
}

public class Client {
  public static void main(String[] args) {
    Receiver r = new Receiver();
    Command c = new ConcreteCommand(r);
    Invoker i = new Invoker();

    i.setCommand(c);
    i.executeCommand();
  }
}

C:\JavaHello\Command>java Client
Receiver action()メソッド

C:\JavaHello\Command>