JAVA存取对象属性时，如果开程多线程，记得对相关存取方法作原子化操作定义

class BankAccount {
    private int balance = 100;
    public int getBalance() {
        return balance;
    }
    public void withdraw(int amount) {
        balance = balance - amount;
    }
}
public class RyanAndMonicaJob implements Runnable {
    private BankAccount account = new BankAccount();

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        RyanAndMonicaJob theJob = new RyanAndMonicaJob();
        Thread one = new Thread(theJob);
        Thread two = new Thread(theJob);
        one.setName("Ryan");
        two.setName("Monica");
        one.start();
        two.start();

    }
    public void run() {
        for (int x = 0; x < 10; x++) {
            makeWithdrawal(10);
            if (account.getBalance() < 0) {
                System.out.println("Overdrawn!");
            }
        }
    }
    private synchronized void makeWithdrawal(int amount) {
        if (account.getBalance() >= amount) {
            System.out.println(Thread.currentThread().getName() + " is about to withdraw");
            try {
                System.out.println(Thread.currentThread().getName() + " is going to sleep");
                Thread.sleep(500);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + " woke up.");
            account.withdraw(amount);
            System.out.println(Thread.currentThread().getName() + " completes the withdrawl");
        } else {
            System.out.println("Sorry, not enough for " + Thread.currentThread().getName());
        }
        
    }

}