Enum을 사용한 State 패턴

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public class VendingMachine {     private enum State {         Selling {             @Override             public void sendMessage() {                 System.out.println("Selling");             }         },         SoldOut {             @Override             public void sendMessage() {                 System.out.println("Sold out");             }         };         public abstract void sendMessage();     }           private State state;           public VendingMachine() {         setState(State.Selling);     }           public void pullLever() {         if(state == State.SoldOut) {             System.out.println("Already sold out");         } else if(new Random().nextBoolean()) {             setState(State.SoldOut);         } else {             state.sendMessage();         }     }           private void setState(State state) {         this.state = state;         state.sendMessage();     }           public static void main(String[] args) {         VendingMachine machine = new VendingMachine();         for(int i = 0; i < 10; i++) {             System.out.print("Pull the lever: ");             machine.pullLever();         }     } }