public void doRentalVideo(Video rentalVideo){
		for(int i=0;i<rentalVideos.length;i++){
			if(rentalVideos[i]==null){
				rentalVideos[i]=rentalVideo;
				break;
			}
			if(i==rentalCDs.length){
				System.out.println("既に2枚借りています");
			}
		}
	}