public static void main(String[] args) { 
  Context context;   
  //ոյʱһ 
  System.out.println("-----------ոյʱһ-------------"); 
  context = new Context(new BackDoor()); //õ 
  context.operate();  //ִ 
  System.out.println("\n\n\n\n\n\n\n\n"); 
   
   //ֲ˼ˣڶ 
  System.out.println("-----------ֲ˼ˣڶ-------------"); 
  context = new Context(new GivenGreenLight()); 
  context.operate();  //ִ˵ڶ 
  System.out.println("\n\n\n\n\n\n\n\n"); 
   
   //ȨС׷ˣզ죿 
  System.out.println("-----------ȨС׷ˣզ죿-------------"); 
  context = new Context(new BlockEnemy()); 
  context.operate();  //˱ 
  System.out.println("\n\n\n\n\n\n\n\n"); 
   
   /* 
   *ˣʵʲ֪Ǹѽֻ֪һң 
   *֪BackDoorƣզ죿  ƺģʽѾѼıд 
   * 
   * BackDoorGivenGreenLightBlockEnemyֻһ룬дfirstsecondthirdû˻˵! 
   *  
   * ģʽĺôǣ˸ھ۵ϵѽȱǸһȥٲ 
   */ 
 }