/**
 * A concrete state for generating bill
 */
import java.io.*;

public class GenerateBill extends ShopState {
 public static boolean instanceFlag = false; //true if have 1 instance
 private GenerateBill() {
 }
 public static GenerateBill getInstance() {
 if(! instanceFlag) {
 instanceFlag = true;
 return new GenerateBill();
 }
 return null;
 }
 public void generateBill() {
 System.out.println("The state is generating bill now !");
 }
}