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://HdhCmsTestcnblogs测试数据/testero/p/15135598.html
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