/**
 * The context for user useing
 */
public class ShopContext {
 private ShopState currentState;
 public ShopContext() {
 }
 public void changeState(ShopState s) {
 currentState = s;
 }
 public void shop() {
 currentState.shop();
 }
 public void generateBill() {
 currentState.generateBill();
 }
 public void pay() {
 currentState.pay();
 }
}