目錄同步代碼塊同步方法lock鎖同步代碼塊

基本語句

synchronized (任意對象) {

操作共享代碼

}

代碼示例

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 + '張票'); 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(); }}

優缺點：

解決了多線程的數據安全問題 多線程時，每個線程都會判斷同步上的鎖，耗費資源，降低了程序的運行效率同步方法

同步方法：將synchronized關鍵字加到方法上

格式: 修飾符 synchronized 返回值類型 方法名(){ } 同步方法的鎖對象是this

同步靜態方法，就是把synchronized關鍵字加到靜態方法上

格式: 修飾符 static synchronized 返回值類型 方法名(){ } 同步靜態方法的鎖對象是 類名.class

代碼示例

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 + '張票');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 + '張票');//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 + '張票');//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 + '張票');//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 + '張票'); 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鎖

lock實現提供比使用synchronized方法和語句可獲得更廣泛的操作

void lock()獲得鎖 void unlock()釋放

lock是接口不能直接實例化，采用實現類實例化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 + '張票'); 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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