同步代码块
基本语句
synchronized (任意对象) {
操作共享代码
}
代码示例
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public class SellTicket implements Runnable { private int tickets = 100; private Object object = new Object(); @Override public void run() { while (true) { synchronized (object) { if (tickets > 0) { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票"); tickets--; } } } } public static void main(String[] args) { SellTicket sellTicket = new SellTicket(); Thread thread1 = new Thread(sellTicket, "窗口1"); Thread thread2 = new Thread(sellTicket, "窗口2"); Thread thread3 = new Thread(sellTicket, "窗口3"); thread1.start(); thread2.start(); thread3.start(); }} |
优缺点：
- 解决了多线程的数据安全问题
- 多线程时，每个线程都会判断同步上的锁，耗费资源，降低了程序的运行效率
同步方法
同步方法：将synchronized关键字加到方法上
- 格式: 修饰符 synchronized 返回值类型 方法名(){ }
- 同步方法的锁对象是this
同步静态方法，就是把synchronized关键字加到静态方法上
- 格式: 修饰符 static synchronized 返回值类型 方法名(){ }
- 同步静态方法的锁对象是 类名.class
代码示例
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public class SellTicket implements Runnable {// private int tickets = 100; private static int tickets = 100; private Object object = new Object(); private int x = 0; @Override public void run() { while (true) { if (x % 2 == 0) {// synchronized (object) {// synchronized (this) { synchronized (SellTicket.class) { if (tickets > 0) { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票"); tickets--; } } } else {// synchronized (object) {// if (tickets > 0) {// try {// Thread.sleep(100);// } catch (InterruptedException e) {// e.printStackTrace();// }// System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");// tickets--;// }// } sellTicket(); } x++; } }// private void sellTicket(){// synchronized (object) {// if (tickets > 0) {// try {// Thread.sleep(100);// } catch (InterruptedException e) {// e.printStackTrace();// }// System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");// tickets--;// }// }// }// private synchronized void sellTicket(){// if (tickets > 0) {// try {// Thread.sleep(100);// } catch (InterruptedException e) {// e.printStackTrace();// }// System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");// tickets--;// } private static synchronized void sellTicket(){ if (tickets > 0) { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票"); tickets--; } } public static void main(String[] args) { SellTicket sellTicket = new SellTicket(); Thread thread1 = new Thread(sellTicket, "窗口1"); Thread thread2 = new Thread(sellTicket, "窗口2"); Thread thread3 = new Thread(sellTicket, "窗口3"); thread1.start(); thread2.start(); thread3.start(); }} |
lock锁
lock实现提供比使用synchronized方法和语句可获得更广泛的操作
- void lock()获得锁
- void unlock()释放
lock是接口不能直接实例化，采用实现类实例化ReentrantLock
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import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class SellTicket implements Runnable { private int tickets = 100; private Object object = new Object(); private Lock lock = new ReentrantLock(); @Override public void run() { while (true) { try { lock.lock(); if (tickets > 0) { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票"); tickets--; } } finally { lock.unlock(); } } } public static void main(String[] args) { SellTicket sellTicket = new SellTicket(); Thread thread1 = new Thread(sellTicket, "窗口1"); Thread thread2 = new Thread(sellTicket, "窗口2"); Thread thread3 = new Thread(sellTicket, "窗口3"); thread1.start(); thread2.start(); thread3.start(); }<br type="_moz"> |
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原文链接：https://www.cnblogs.com/testero/p/15135598.html
