以下是一个模拟订票业务的程序。BookingClerk类代表自动售票员，其中包含一个订票（booking）方法。假设一开始有10张票可预定。程序运行时产生两个订票客户同时自动向自动售票员订票。请问会出现什么错误？该如何修改public class Test {public static void main(String args[]) {BookingClerk bt = new BookingClerk();new BookingTest(bt, 7);new BookingTest(bt, 5);}}class BookingClerk {int remainder = 10;void booking(int num) {if (num <= remainder) {System.out.println("预定" + num + "张票");try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}remainder = remainder - num;}else {System.out.println("剩余票不够，无法预定");}System.out.println("还剩"+remainder+"张票");}}class BookingTest implements Runnable {BookingClerk bt;int num;BookingTest(BookingClerk bt, int num) {this.bt = bt;this.num = num;new Thread(this).start();}public void run() {bt.booking(num);}}