Java基础复习：线程练习2-优快云博客

本文探讨了多线程环境下实现售票同步的三种方法：使用同步代码块、同步方法及可重入锁。通过对比不同同步机制的特点，帮助读者理解如何有效避免线程间的资源竞争。

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修改练习1卖票例子，先让它网络延迟，出现问题，再解决问题。

1）同步代码块

class Ticket implements Runnable {
	private Integer num = 50;

	@Override
	public void run() {
		for (int i = 0; i < 200; i++) {
			sale();
		}
	}

	private Object o = new Object();// 作为监听对象

	/**
	 * 卖票
	 */
	public void sale() {
		synchronized (o) {
			if (num > 0) {
				try {
					Thread.sleep(1);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				System.out.println(Thread.currentThread().getName() + "卖出了第"
						+ num-- + "张票");
			}
		}
	}

}

public class TicketDemo {
	public static void main(String[] args) {
		Runnable target = new Ticket();
		new Thread(target, "A").start();
		new Thread(target, "B").start();
		new Thread(target, "C").start();
	}
}

2）方法2：同步方法

class Ticket implements Runnable {
	private Integer num = 50;

	@Override
	public void run() {
		for (int i = 0; i < 200; i++) {
			sale();
		}
	}

	/**
	 * 卖票
	 */
	public synchronized void sale() {
		if (num > 0) {
			try {
				Thread.sleep(1);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName() + "卖出了第"
					+ num-- + "张票");
		}
	}

}

public class TicketDemo {
	public static void main(String[] args) {
		Runnable target = new Ticket();
		new Thread(target, "A").start();
		new Thread(target, "B").start();
		new Thread(target, "C").start();
	}
}

3）可重入锁

import java.util.concurrent.locks.ReentrantLock;

class Ticket implements Runnable {
	private Integer num = 50;
	private ReentrantLock lock = new ReentrantLock();

	@Override
	public void run() {
		for (int i = 0; i < 200; i++) {
			sale();
		}
	}

	/**
	 * 卖票
	 */
	public void sale() {
		lock.lock();
		if (num > 0) {
			try {
				Thread.sleep(1);
				System.out.println(Thread.currentThread().getName() 
						+ "卖出了第" + num-- + "张票");
			} catch (Exception e) {
				e.printStackTrace();
			} finally {
				lock.unlock();
			}
		}
	}

}

public class TicketDemo {
	public static void main(String[] args) {
		Runnable target = new Ticket();
		new Thread(target, "A").start();
		new Thread(target, "B").start();
		new Thread(target, "C").start();
	}
}