[medium snippets] #medium #designPattern #CommandPattern

Client.java

public class Client {
  static public void main(String[] args) {
    CommandA commandA = new CommandA(new ReceiverA());
    CommandB commandB = new CommandB(new ReceiverB());
    
    Invoker invoker = new Invoker();
    invoker.setCommand(0, commandA);
    invoker.setCommand(1, commandB);
    
    invoker.onButtonWasPushed(0);
    invoker.onButtonWasPushed(1);
    invoker.undoButtonWasPushed();
    invoker.onButtonWasPushed(1);
  }
}