Java线程同步的四种方式详解

synchronized(对象) { //得到对象的锁，才能操作同步代码
    需要被同步代码;
}

public class SynchronizedThread {
 
    class Bank {
 
        private int account = 200;
 
        public int getAccount() {
            return account;
        }
 
        
        public synchronized void save(int money) {
            account += money;
        }
 
        
        public void save1(int money) {
            synchronized (this) {
                account += money;
            }
        }
    }
 
    class NewThread implements Runnable {
        private Bank bank;
 
        public NewThread(Bank bank) {
            this.bank = bank;
        }
 
        @Override
        public void run() {
            for (int i = 0; i < 10; i++) {
                // bank.save1(10);
                bank.save(10);
                System.out.println(i + "账户余额为：" + bank.getAccount());
            }
        }
 
    }
 
    
    public void useThread() {
        Bank bank = new Bank();
        NewThread new_thread = new NewThread(bank);
        System.out.println("线程1");
        Thread thread1 = new Thread(new_thread);
        thread1.start();
        System.out.println("线程2");
        Thread thread2 = new Thread(new_thread);
        thread2.start();
    }
 
    public static void main(String[] args) {
        SynchronizedThread st = new SynchronizedThread();
        st.useThread();
    }
 
}

private int account = 100;
//需要声明这个锁
private Lock lock = new ReentrantLock();
public int getAccount() {
    return account;
}
//这里不再需要synchronized 
public void save(int money) {
    lock.lock();
    try{
        account += money;
    }finally{
        lock.unlock();
    }

}

private AtomicInteger account = new AtomicInteger(100);

public AtomicInteger getAccount() {
    return account;
}

public void save(int money) {
    account.addAndGet(money);
}

//只改Bank类，其余代码与上同
public class Bank{
    // 创建一个线程本地变量 ThreadLocal
    private static ThreadLocal<Integer> account = new ThreadLocal<Integer>(){
        @Override
        //返回当前线程的"初始值" 
        protected Integer initialValue(){
            return 100;
        }
    };
    public void save(int money){
        //设置线程副本中的值
        account.set(account.get()+money);
    }
    public int getAccount(){
        //返回线程副本中的值 
        return account.get();
    }
}