Java多线程下解决数据安全问题
基本语句
synchronized (任意对象) {
操作共享代码
}
代码示例
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
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
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(); }
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