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

最显著的应用当然是银行存款和取款，不要存在存取数字和实际发生不一样的情况。

synchronized关键字。

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());
        }

    }

}

Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Ryan is about to withdraw
Ryan is going to sleep
Ryan woke up.
Ryan completes the withdrawl
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica
Sorry, not enough for Monica