private void operation() throws SQLException {
		System.out
				.println("Please choose your operation:\n1 add a new URL"
						+ "\t2 delete a URL\t3 display all\n4 update DB\t5 delete table\t6 Exit this application");
		try {
			int input = sc.nextInt();
			switch (input) {
			case 1:
				add();
				break;
			case 2:
				delete();
				break;
			case 3:
				display();
				break;
			case 4:
				update();
				break;
			case 5:
				deleteTable();
				break;
			case 6:
				closeDB();
				break;
			default:
				System.out.println("input error, please input vaild number");
				break;
			}
		} catch (Exception e) {
			System.out.println("input error, please input vaild number");
			System.out.println(e);
		}
		this.operation();
	}