synchronized keyword DEMO

最新推荐文章于 2021-04-08 15:09:45 发布

转载最新推荐文章于 2021-04-08 15:09:45 发布 · 687 阅读

Head First Java 专栏收录该内容

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本文探讨了并发环境中银行账户的余额操作，通过Bob和Monica的实例展示了线程安全问题，包括账户余额的同步更新与不足金额时的错误处理。

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package HeadFirstJava;

class BankAccount {
    private int balance = 100;
    
    public int getBalance() {
        return balance;
    }
    public void withdraw(int amount) {
        balance = balance - amount;
    }
}

class BobAndMonica implements Runnable {
    private BankAccount account = new BankAccount();

    public static void main(String[] args) {
        BobAndMonica theJob = new BobAndMonica();
        Thread one = new Thread(theJob);
        Thread two = new Thread(theJob);
        one.setName("Bob");
        two.setName("Monica");
        one.start();
        two.start();
    }
    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int x = 0; x < 10; x++) {
            makeWithdrawl(10);
        }
        if (account.getBalance() < 0) {
            System.out.println("Overdrawn");
        }
    }
    private synchronized void makeWithdrawl(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());    
        }
    }
    
}

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