public void book_update() throws Exception{
		int field = 0, updatecomplete =1;
		Book findbook = bookcollect.book_search_lib();
		// Ȥ ISBN ˻  å findbook̶ Bookü Ϲ޴´.
		if (findbook == null){
			librarian_menu(); //˻ å̾ٸ 缭Ǹ޴εư.
		}else{ //Ʈϰ   Ʈ ׸ Է¹޴´.
			do{
				System.out.println("Ʈ  ׸ ȣ ּ.\n1.  \n2.  \n3. ǻ \n4. ISBN \n5.   \n6. 뿩\nԷ :");
				field = scan.nextInt();
				//Ʈ ׸ Ʈ Bookü Լ Ѱش.
				findbook=bookcollect.updatefield(field, findbook);
				//Ʈ  findbook Ϲ޴´.
				System.out.println(""+'\t'+ ""+ '\t'+"ǻ"+'\t'+"ISBN"+'\t'+"⿩"+'\t'+"뿩");	
				System.out.println("*******************************************************************");
				System.out.println(findbook.toString());
				bookcollect.savenow();
				//Ʈ    Ͽ Ѵ.
				System.out.println("ش   Ʈ  Ͻðڽϱ?(Y/N)");
				scan.nextLine();
				String updatecheck = scan.nextLine();
				// ش   Ʈ Ѵٸ Ǯ̵ǵ Ѵ.
				if (updatecheck.equals("Y")) {
					updatecomplete =1;
				} 
				else if (updatecheck.equals("N")) {
					updatecomplete = 0;
					librarian_menu();
				}
			}while(updatecomplete ==1);
		}
	}