1、在Java語(yǔ)言中，引入對(duì)象互斥鎖的概念，保證共享數(shù)據(jù)操作的完整性。每個(gè)對(duì)象都對(duì)應(yīng)于一個(gè)可稱為互斥鎖的標(biāo)記，這個(gè)標(biāo)記保證在任一時(shí)刻，只能有一個(gè)線程訪問(wèn)對(duì)象。關(guān)鍵字synchronized用來(lái)給對(duì)象加互斥鎖。三國(guó)1同步非靜態(tài)方法：synchronized放在方法聲明中，表示整個(gè)方法為同步方法,鎖定this對(duì)象,如果有一個(gè)線程進(jìn)入了該方法,其他線程要想使用當(dāng)前this對(duì)象的任何同步方法,都必須等待前一個(gè)線程執(zhí)行完該同步方法之后public synchronized void method1() public synchronized void method2() public synchronize

2、d void method3() 同步static方法： synchronized放在static方法聲明中,表示鎖定該類(lèi)的class對(duì)象如果有一個(gè)線程進(jìn)入了該方法,其他線程要想使用當(dāng)前類(lèi)中的任何同步靜態(tài)方法,都必須等待前一個(gè)線程執(zhí)行完該同步方法之后;其他非同步方法及非靜態(tài)的同步方法的執(zhí)行不受影響.3public synchronized static void method1() public synchronized static void method2() 同步代碼塊：synchronized放在對(duì)象前面限制一段代碼的執(zhí)行4Object obj = new Object();.sync

3、hronized(this)/this被加鎖,任何其他要鎖this的代碼塊被阻塞. 需要同步的代碼;.synchronized(obj)/obj被加鎖,任何其他要鎖obj的代碼塊被阻塞. 需要同步的代碼;.class TicketOffice implements Runnable private int tickets = 0; private boolean flag =true; public void run() while (flag) try Thread.sleep(10); catch (InterruptedException e) e.printStackTrace();

4、if (tickets 100) tickets+; System.out.println(Thread.currentThread().getName()+ :賣(mài)出第 + tickets + 張票); else flag = false; public class TestTicketOffice public static void main(String args) TicketOffice off = new TicketOffice(); Thread thread1 = new Thread(off); thread1.setName(售票點(diǎn)1); thread1.start();

5、 5售票案例中出現(xiàn)的數(shù)據(jù)不一致問(wèn)題class TicketOffice implements Runnable private int tickets = 0; private boolean flag = true; public void run() while (flag) try Thread.sleep(10); catch (InterruptedException e) e.printStackTrace(); synchronized(this) if (tickets 100) tickets+; System.out.println(Thread.currentThread

6、().getName()+ :賣(mài)出第 + tickets + 張票); else flag = false; public synchronized void sale() if (tickets 100) tickets+; System.out.println(Thread.currentThread().getName() + :賣(mài)出第 + tickets + 張票); else flag = false; 6當(dāng)run()方法體內(nèi)的代碼操作到了成員變量(共享數(shù)據(jù))時(shí)，就可能會(huì)出現(xiàn)多線程安全問(wèn)題(線程不同步問(wèn)題)。編程技巧在方法中盡量少操作成員變量，多使用局部變量7public class

7、 TestSyncExercise public static void main(String args) MyRunn run = new MyRunn(); Thread thread1 = new Thread(run); thread1.start(); try Thread.sleep(1000); catch (InterruptedException e) e.printStackTrace(); run.test2(); class MyRunn implements Runnable private int count = 100; public void run() te

8、st1(); public synchronized void test1() System.out.println(test1開(kāi)始執(zhí)行,把count改成1000); count = 1000; try Thread.sleep(5000); catch (InterruptedException e) e.printStackTrace(); System.out.println(test1:count= + count); public void test2() System.out.println(test2開(kāi)始執(zhí)行,把count改成2000); count = 2000; System

9、.out.println(test2:count= + count); TestSyncExercise.java8同步練習(xí)設(shè)計(jì)一個(gè)銀行賬戶Account類(lèi)(name,money, saveOrWithdrawMoney(int x),定義一個(gè)線程類(lèi)MyThread 一個(gè)場(chǎng)景類(lèi)AccountTest,創(chuàng)建一個(gè)Account對(duì)象, 創(chuàng)建多個(gè)線程類(lèi)的對(duì)象,通過(guò)線程類(lèi)的構(gòu)造方法傳入同一個(gè)Account的對(duì)象和增減的錢(qián)數(shù),并啟動(dòng),模擬銀行卡存取錢(qián)的過(guò)程;分別不使用/使用同步,觀察結(jié)果同步效果:現(xiàn)在有錢(qián):1000準(zhǔn)備再存100存完,現(xiàn)在有錢(qián):1100現(xiàn)在有錢(qián):1100準(zhǔn)備再存400存完,現(xiàn)在有錢(qián):150

10、0現(xiàn)在有錢(qián):1500準(zhǔn)備再取-100取完,現(xiàn)在有錢(qián):1400場(chǎng)景類(lèi)代碼提示見(jiàn)下頁(yè)同步練習(xí)Account account = new Account(zhangsan,1000);MyThread t1 = new MyThread(account, 100);MyThread t2 = new MyThread(account, -100);MyThread t3 = new MyThread(account, 400);t1.start();t2.start();t3.start();在線程類(lèi)MyThread的run()方法中調(diào)用saveOrWithdrawMoney集合容器類(lèi)的線程安全性的

11、問(wèn)題Runnable實(shí)現(xiàn)類(lèi):ArrayList al = new ArrayList();/List al2 = Collections.synchronizedList(al);/Vector al3 = new Vector();public void run() for(int i = 0;i 10000;i+)/synchronized(al)al.add(i);al.add(i);System.out.println(Thread.currentThread().getName() +已經(jīng)運(yùn)行完畢);死鎖的原因：線程1鎖住資源A等待資源B，線程2鎖住資源B等待資源A，兩個(gè)線程都在等待

12、自己需要的資源，而這些資源被另外的線程鎖住，這些線程你等我，我等你，誰(shuí)也不愿意讓出資源，這樣死鎖就產(chǎn)生了。12public class TestDeadLock implements Runnable public boolean flag = true; private static Object res1 = new Object(); private static Object res2 = new Object(); public void run() if (flag) /* 鎖定資源res1 */ synchronized (res1) System.out.println(鎖定資

13、源1，等待資源2.); try Thread.sleep(1000); catch (InterruptedException e) /* 鎖定資源res2 */ synchronized (res2) System.out.println(Complete.); else /* 鎖定資源res2 */ synchronized (res2) System.out.println(鎖定資源2，等待資源1*); try Thread.sleep(1000); catch (InterruptedException e) /* 鎖定資源res1 */ synchronized (res1) System.out.println(Complete.); public static void mai