并发编程实战 2.1. 使用synchronized实现同步

如果一个对象的方法已用synchronized关键字声明，那么只有一个线程被允许访问它。如果其他线程想要访问这个对象的其他方法，它将被挂起，直到第一个线程执行完正在执行的方法。

静态方法则有不同的行为。用synchronized声明的静态方法，同时只能被一个线程访问，但是其他线程可以访问这个对象的非静态方法。会造成数据不一致的错误。

范例：两个线程：银行存钱，公司取钱；一个实体类：账户，并带有存钱与取钱的方法。

账户：

package com.rr.concurrent.chapter2.recipe1.test; import java.util.concurrent.TimeUnit; /** * Created by isaac_gu on 2016/5/12. */ public class Account { private int balance; public Account(int balance) { this.balance = balance; } public int getBalance() { return balance; } public void setBalance(int balance) { this.balance = balance; } public synchronized void saveMoney(int amount) { int temp = balance; try { TimeUnit.MILLISECONDS.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } temp += amount; balance = temp; System.out.println("saveMoney:" + balance); } public synchronized void drawMoney(int amount) { int temp = balance; try { TimeUnit.MILLISECONDS.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } temp -= amount; balance = temp; System.out.println("drawMoney:" + balance); } }

银行：

package com.rr.concurrent.chapter2.recipe1.test; /** * Created by isaac_gu on 2016/5/12. * 银行负责存钱 */ public class Bank implements Runnable { private Account account; public Bank(Account account) { this.account = account; } @Override public void run() { for (int i = 0, len = 100; i < len; i++) { account.saveMoney(1000); } } }

公司：

package com.rr.concurrent.chapter2.recipe1.test; /** * Created by isaac_gu on 2016/5/12. * 公司负责取钱 */ public class Company implements Runnable { private Account account; public Company(Account account) { this.account = account; } @Override public void run() { for (int i = 0, len = 100; i < len; i++) { account.drawMoney(1000); } } }

测试：

package com.rr.concurrent.chapter2.recipe1.test; /** * Created by isaac_gu on 2016/5/12. * 范例：两个线程：银行存钱，公司取钱；一个实体类：账户，并带有存钱与取钱的方法。 */ public class Test { public static void main(String[] args) { Account account = new Account(100000); Thread bankThread = new Thread(new Bank(account)); Thread companyThread = new Thread(new Company(account)); System.out.println("START - balance: " + account.getBalance()); bankThread.start(); companyThread.start(); try { bankThread.join(); companyThread.join(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("END - balance: "+ account.getBalance()); } }

同步的结果：

START - balance: 100000 saveMoney:101000 saveMoney:102000 saveMoney:103000 saveMoney:104000 saveMoney:105000 saveMoney:106000 saveMoney:107000 saveMoney:108000 drawMoney:107000 drawMoney:106000 drawMoney:105000 drawMoney:104000 drawMoney:103000 drawMoney:102000 drawMoney:101000 drawMoney:100000 drawMoney:99000 drawMoney:98000 drawMoney:97000 drawMoney:96000 drawMoney:95000 drawMoney:94000 drawMoney:93000 drawMoney:92000 drawMoney:91000 drawMoney:90000 drawMoney:89000 drawMoney:88000 drawMoney:87000 drawMoney:86000 drawMoney:85000 drawMoney:84000 drawMoney:83000 drawMoney:82000 drawMoney:81000 drawMoney:80000 drawMoney:79000 drawMoney:78000 drawMoney:77000 drawMoney:76000 drawMoney:75000 drawMoney:74000 drawMoney:73000 drawMoney:72000 drawMoney:71000 drawMoney:70000 drawMoney:69000 drawMoney:68000 drawMoney:67000 drawMoney:66000 drawMoney:65000 drawMoney:64000 drawMoney:63000 drawMoney:62000 drawMoney:61000 drawMoney:60000 drawMoney:59000 drawMoney:58000 drawMoney:57000 drawMoney:56000 drawMoney:55000 drawMoney:54000 drawMoney:53000 drawMoney:52000 drawMoney:51000 drawMoney:50000 drawMoney:49000 drawMoney:48000 drawMoney:47000 drawMoney:46000 drawMoney:45000 drawMoney:44000 drawMoney:43000 drawMoney:42000 drawMoney:41000 drawMoney:40000 drawMoney:39000 drawMoney:38000 drawMoney:37000 drawMoney:36000 drawMoney:35000 drawMoney:34000 drawMoney:33000 drawMoney:32000 drawMoney:31000 drawMoney:30000 drawMoney:29000 drawMoney:28000 drawMoney:27000 drawMoney:26000 drawMoney:25000 drawMoney:24000 drawMoney:23000 drawMoney:22000 drawMoney:21000 drawMoney:20000 drawMoney:19000 drawMoney:18000 drawMoney:17000 drawMoney:16000 drawMoney:15000 drawMoney:14000 drawMoney:13000 drawMoney:12000 drawMoney:11000 drawMoney:10000 drawMoney:9000 drawMoney:8000 saveMoney:9000 saveMoney:10000 saveMoney:11000 saveMoney:12000 saveMoney:13000 saveMoney:14000 saveMoney:15000 saveMoney:16000 saveMoney:17000 saveMoney:18000 saveMoney:19000 saveMoney:20000 saveMoney:21000 saveMoney:22000 saveMoney:23000 saveMoney:24000 saveMoney:25000 saveMoney:26000 saveMoney:27000 saveMoney:28000 saveMoney:29000 saveMoney:30000 saveMoney:31000 saveMoney:32000 saveMoney:33000 saveMoney:34000 saveMoney:35000 saveMoney:36000 saveMoney:37000 saveMoney:38000 saveMoney:39000 saveMoney:40000 saveMoney:41000 saveMoney:42000 saveMoney:43000 saveMoney:44000 saveMoney:45000 saveMoney:46000 saveMoney:47000 saveMoney:48000 saveMoney:49000 saveMoney:50000 saveMoney:51000 saveMoney:52000 saveMoney:53000 saveMoney:54000 saveMoney:55000 saveMoney:56000 saveMoney:57000 saveMoney:58000 saveMoney:59000 saveMoney:60000 saveMoney:61000 saveMoney:62000 saveMoney:63000 saveMoney:64000 saveMoney:65000 saveMoney:66000 saveMoney:67000 saveMoney:68000 saveMoney:69000 saveMoney:70000 saveMoney:71000 saveMoney:72000 saveMoney:73000 saveMoney:74000 saveMoney:75000 saveMoney:76000 saveMoney:77000 saveMoney:78000 saveMoney:79000 saveMoney:80000 saveMoney:81000 saveMoney:82000 saveMoney:83000 saveMoney:84000 saveMoney:85000 saveMoney:86000 saveMoney:87000 saveMoney:88000 saveMoney:89000 saveMoney:90000 saveMoney:91000 saveMoney:92000 saveMoney:93000 saveMoney:94000 saveMoney:95000 saveMoney:96000 saveMoney:97000 saveMoney:98000 saveMoney:99000 saveMoney:100000 END - balance: 100000

去掉synchronized的结果

START - balance: 100000 saveMoney:101000 drawMoney:99000 saveMoney:102000 drawMoney:98000 saveMoney:103000 drawMoney:97000 saveMoney:104000 drawMoney:96000 saveMoney:105000 drawMoney:95000 saveMoney:106000 drawMoney:94000 saveMoney:107000 drawMoney:93000 saveMoney:108000 drawMoney:92000 saveMoney:109000 drawMoney:91000 saveMoney:110000 drawMoney:90000 saveMoney:111000 drawMoney:89000 drawMoney:88000 saveMoney:112000 saveMoney:113000 drawMoney:87000 saveMoney:114000 drawMoney:86000 drawMoney:85000 saveMoney:85000 saveMoney:86000 drawMoney:84000 drawMoney:83000 saveMoney:83000 saveMoney:84000 drawMoney:84000 drawMoney:83000 saveMoney:85000 saveMoney:86000 drawMoney:84000 drawMoney:85000 saveMoney:85000 saveMoney:86000 drawMoney:84000 saveMoney:83000 drawMoney:83000 drawMoney:82000 saveMoney:84000 saveMoney:85000 drawMoney:81000 saveMoney:86000 drawMoney:80000 drawMoney:79000 saveMoney:79000 drawMoney:78000 saveMoney:80000 drawMoney:77000 saveMoney:81000 drawMoney:80000 saveMoney:82000 saveMoney:83000 drawMoney:81000 drawMoney:80000 saveMoney:84000 drawMoney:79000 saveMoney:85000 drawMoney:78000 saveMoney:86000 drawMoney:77000 saveMoney:87000 drawMoney:76000 saveMoney:88000 drawMoney:75000 saveMoney:89000 drawMoney:74000 saveMoney:90000 drawMoney:73000 saveMoney:91000 drawMoney:72000 saveMoney:92000 drawMoney:71000 saveMoney:93000 drawMoney:70000 saveMoney:94000 drawMoney:69000 saveMoney:95000 drawMoney:68000 saveMoney:96000 drawMoney:67000 saveMoney:97000 drawMoney:66000 saveMoney:98000 drawMoney:65000 saveMoney:99000 drawMoney:64000 saveMoney:100000 drawMoney:63000 saveMoney:101000 drawMoney:62000 saveMoney:102000 drawMoney:61000 saveMoney:103000 drawMoney:60000 saveMoney:104000 drawMoney:59000 saveMoney:105000 drawMoney:58000 saveMoney:106000 drawMoney:57000 saveMoney:107000 drawMoney:56000 saveMoney:108000 drawMoney:55000 saveMoney:109000 drawMoney:54000 saveMoney:110000 drawMoney:53000 saveMoney:111000 drawMoney:52000 saveMoney:112000 saveMoney:113000 drawMoney:51000 drawMoney:50000 saveMoney:114000 drawMoney:49000 saveMoney:115000 saveMoney:116000 drawMoney:48000 drawMoney:47000 saveMoney:117000 drawMoney:116000 saveMoney:116000 saveMoney:117000 drawMoney:115000 saveMoney:118000 drawMoney:114000 saveMoney:115000 drawMoney:113000 saveMoney:114000 drawMoney:112000 saveMoney:113000 drawMoney:111000 drawMoney:110000 saveMoney:112000 saveMoney:111000 drawMoney:111000 saveMoney:112000 drawMoney:112000 saveMoney:113000 drawMoney:111000 saveMoney:114000 drawMoney:110000 saveMoney:115000 drawMoney:109000 drawMoney:108000 saveMoney:116000 saveMoney:117000 drawMoney:107000 saveMoney:118000 drawMoney:106000 drawMoney:105000 saveMoney:119000 saveMoney:120000 drawMoney:104000 drawMoney:103000 saveMoney:121000 drawMoney:102000 saveMoney:122000 drawMoney:101000 saveMoney:123000 drawMoney:100000 saveMoney:124000 drawMoney:99000 saveMoney:125000 saveMoney:126000 drawMoney:98000 saveMoney:127000 drawMoney:97000 saveMoney:128000 drawMoney:96000 saveMoney:129000 drawMoney:95000 saveMoney:130000 drawMoney:94000 saveMoney:131000 drawMoney:93000 saveMoney:132000 drawMoney:92000 drawMoney:91000 saveMoney:133000 drawMoney:90000 saveMoney:134000 saveMoney:135000 drawMoney:133000 drawMoney:132000 saveMoney:136000 saveMoney:137000 drawMoney:131000 drawMoney:130000 saveMoney:132000 END - balance: 132000 相关资源：Java 并发编程实战 学习分享.ppt