[medium snippets] #medium #designPattern #CommandPattern

Invoker.java

public class Invoker {
  private Command[] commands;
  private Command undoCommand;

  public Invoker() {
    commands = new Command[2];
    undoCommand = new NoCommand();
  }
  
  public void setCommand(int slot, Command command) {
    commands[slot] = command;
  }
  
  public void onButtonWasPushed(int slot) {
    commands[slot].execute();
    undoCommand = commands[slot];
  }
  
  public void undoButtonWasPushed() {
    undoCommand.undo();
  }
}