如何在Java中实现同步：面试问题及解决方法-蒲公英云

如何在Java中实现同步：面试问题及解决方法

在Java中实现同步主要依赖于两个重要的特性：互斥性和条件变量。

互斥锁（Synchronized）：
这是最基础的同步机制。当一个线程进入synchronized代码块时，会获取到当前对象的锁，其他线程必须等到这个锁被释放才能执行。

public class Counter {
    private int count;
    public synchronized void increment() {
        count++;
    }
    public synchronized int decrement() {
        if (count > 0) {
            count--;
            return count;
        } else {
            throw new IllegalArgumentException("Counter is already at zero!");
        }
    }
    // getter for count
}

条件变量（Condition）：
当一个线程等待特定条件满足时，可以使用条件变量。通常与synchronized一起使用。

public class SleepyThread {
    private final Condition condition;
    private boolean ready;
    public SleepyThread(Condition condition) {
        this.condition = condition;
    }
    // method to wait until ready
    public void awaitReady() throws InterruptedException {
        synchronized (condition) {
            while (!ready) {
                condition.await();
            }
        }
    }
    // method to signal when ready
    public void signalReady() {
        synchronized (condition) {
            ready = true;
            condition.signalAll(); // signal all waiting threads
        }
    }
    // usage example
    public static void main(String[] args) {
        Condition condition = new Condition();
        SleepyThread thread1 = new SleepyThread(condition);
        SleepyThread thread2 = new SleepyThread(condition);
        thread1.awaitReady();
        thread2.signalReady();
        thread1印状态("thread1 ready" + thread1的状态());
        thread2印状态("thread2 ready" + thread2的状态());
        // 按任意键退出
        System.in.read();
    }
}