多线程知识点

* 程序 : 可以执行的保存在硬盘上静态代码
* 进程 : 正在内存中执行中的程序, 有生命周期. 多进程也可以多任务.
* 线程 : 进程中的子任务, 也用于实现多任务
*
* 创建并启动线程的方式
*      1) 实现的方式 : 它比继承的方式更好, 避免单继承局限, 方便的用于共享数据
*          写一个具体类, 实现Runnable, 实现其中的run()方法, 这个方法就是线程体.
*          创建这个具体类的对象, 并把它作为实参再传递给Thread对象的构造中, 创建线程对象
*          调用线程对象的start()
*
*      2) 继承的方式 : 不利于共享数据
*          写一个具体类, 继承Thread, 并重写run方法. 否则这个run方法是空的.run()是线程体
*          创建具体类对象, 相当于创建了Thread对象
*          调用对象的start方法.
*
* void start():  启动线程，并执行对象的run()方法, 激活新栈
* run():  线程在被调度时执行的操作
* String getName():  返回线程的名称
* void setName(String name):设置该线程名称
* static currentThread(): 返回当前线程, 此方法压入哪个栈, 就获取哪个栈的线程对象
* getPriority() ：返回线程优先值, 优先级最高为10, 最小为1
* setPriority(int newPriority) ：改变线程的优先级
* static  void  sleep(long millis)：(指定时间:毫秒)
* 令当前活动线程在指定时间段内放弃对CPU控制,使其他线程有机会被执行,时间到后重排队。
* 抛出InterruptedException异常
*
* 解除sleep阻塞的方法 : 1) 自然醒, 2) 被别的线程调用了本线程对象的interrupt().
*
* 线程生命周期
*                        阻塞   sleep()
*               sleep时间到     b.join()
*               b线程执行完毕   wait()
*               notify()          |
*                  |   获取CPU执行权
* 新建 ---------> 就绪 --------------> 运行 -------------->死亡
*       start()       <--------------          run()结束
*                       失去cpu执行权           stop()
*
* 当前线程的同步方法、同步代码块执行结束
* 当前线程在同步代码块、同步方法中遇到break、return终止了该代码块、该方法的继续执行。
* 当前线程在同步代码块、同步方法中出现了未处理的Error或Exception，导致异常结束
* 当前线程在同步代码块、同步方法中执行了锁对象的wait()方法，当前线程暂停，并释放锁。
*

多线程知识点练习

键盘监听器（以通知的方式结束线程）

//在main方法中创建并启动两个线程。第一个线程循环随机打印100以内的整数，
//直到第二个线程从键盘读取了“Q”命令。

public class CanStopRunnerTest {//在main方法中创建并启动两个线程。第一个线程循环随机打印100以内的整数，//直到第二个线程从键盘读取了“Q”命令。public static void main(String[] args) {Runnable runner = new CanStopRunner();Thread thread = new Thread(runner);thread.setName("打印随机数线程");thread.start();Runnable runner2 = new KeyListener(runner);Thread thread2 = new Thread(runner2);thread2.setName("键盘监听器");thread2.setDaemon(true);    //变成守护线程/*** Java中的线程分为两类：一种是守护线程，一种是用户线程。* 它们在几乎每个方面都是相同的，唯一的区别是判断JVM何时离开。* 守护线程是用来服务用户线程的，通过在start()方法前调用thread.setDaemon(true)可以把一个用户线程变成一个守护线程。* Java垃圾回收就是一个典型的守护线程。* 若JVM中都是守护线程，当前JVM将退出。*/		thread2.start();}
}public class KeyListener implements Runnable {private Runnable runner;public KeyListener(Runnable runner) {this.runner = runner;}@Overridepublic void run() {BufferedReader bufferedReader = null;try {bufferedReader = new BufferedReader(new InputStreamReader(System.in));String line;while ((line = bufferedReader.readLine()) != null) {if (line.equalsIgnoreCase("q")) {((CanStopRunner)runner).setFlag(false);//break; // 自我终结}}} catch (Exception e) {e.printStackTrace();} finally {if (bufferedReader != null) {try {bufferedReader.close();} catch (IOException e) {e.printStackTrace();}}}}
}public class CanStopRunner implements Runnable {private boolean flag = true;public boolean isFlag() {return flag;}public void setFlag(boolean flag) {this.flag = flag;}@Overridepublic void run() {while (flag) {System.out.println(Thread.currentThread().getName() + " : " + (int)(Math.random() * 100));}System.out.println("结束疯狂的打印....");}
}

观察者模式

/*编写程序，在main方法中创建一个线程。线程每隔一定时间（200ms以内的随机时间）产生一个0-100之间的随机整数，打印后将该整数放到集合中；
共产生100个整数，全部产生后，睡眠30秒，然后将集合内容打印输出；
在main线程中，唤醒上述睡眠的线程，使其尽快打印集合内容。*/

public class SleepExerRunnerTest {public static void main(String[] args) {Runnable runner = new SleepExerRunner();Thread thread = new Thread(runner);thread.start();// 主线程要等待/*try {Thread.sleep(20 * 1000);} catch (InterruptedException e) {e.printStackTrace();}*/// 观察者, 不断地观察目标, 有时间间隔.  必须要让线程2睡眠的原因是：让线程一有机会会刷主存中的副本。也可以将线程一的Flag属性用volatile修饰while (!((SleepExerRunner)runner).isFlag()) {try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}}thread.interrupt();  // 打断睡眠的线程}
}public class SleepExerRunner implements Runnable {private boolean flag = false;public boolean isFlag() {return flag;}@Overridepublic void run() {List<Integer> list = new ArrayList<>();for (int i = 0; i < 100; i++) {int rand = (int)(Math.random() * 100);System.out.println(Thread.currentThread().getName() + " : " + rand);list.add(rand);int time = (int)(Math.random() * 200);try {Thread.sleep(time);} catch (InterruptedException e) {System.out.println("在睡[" + time + "]毫秒时被打断");}}flag = true;System.out.println("要睡30秒了....");try {Thread.sleep(30 * 1000);} catch (InterruptedException e) {System.out.println("在睡30秒时被打断 不爽");}System.out.println("我要打印集合内容了");Iterator<Integer> iterator = list.iterator();while (iterator.hasNext()) {Integer next = iterator.next();System.out.println(next);}}
}

线程同步

线程同步在单例模式（懒汉式）中的应用

class Singleton {private static Singleton only;private Singleton() {}public static Singleton getInstance() {if (only == null) {synchronized ("") {if (only == null) {only = new Singleton();}}}return only;}
}public class SingletonTest {public static void main(String[] args) {Runnable runnable = new Runnable() {@Overridepublic void run() {Singleton instance = Singleton.getInstance();System.out.println(Thread.currentThread().getName() + " : " + instance);}};new Thread(runnable).start();new Thread(runnable).start();new Thread(runnable).start();}
}

其他练习

//编写一个线程程序（Counter类），声明实例变量counter，
// 初值为200。在run方法中循环50次，每次对counter做减2操作（用-=实现），
// 睡眠10毫秒，并打印counter值，然后继续下一次循环；/*** 两个同 :*      多个线程 "同时" 修改 "同一" 数据*/

public class CounterTest {public static void main(String[] args) {Runnable runner = new Counter();Thread thread1 = new Thread(runner);thread1.setName("线程1");Thread thread2 = new Thread(runner);thread2.setName("线程2");thread1.start();thread2.start();}
}public class Counter implements Runnable {private int counter = 200;@Override//public synchronized void run() { // 相当于把此方法全部锁定, 同一时间只能有一个线程执行此方法public void run() {//synchronized (this) { // 锁的粒度太大for (int i = 0; i < 50; i++) {synchronized ("") { // (互斥锁), 任意对象都可以作锁. 最好使用一个唯一对象.// 同步块中的代码具有原子性.counter -= 2;try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(Thread.currentThread().getName() + " : " + counter);}}//}}
}

public class HomeWork3 {/*** 3. 取钱取的是100以内的随机钱, 存钱也是100以内的随机钱. 要求余额不为负数.*/public static void main(String[] args) {Account account = new Account("小敏",100);Thread deposit = new Thread(new Deposit2(account));deposit.setName("存款机一：");deposit.start();Thread deposit2 = new Thread(new Deposit2(account));deposit2.setName("存款机二：");deposit2.start();Thread withdraw1 = new Thread(new Withdraw2(account));withdraw1.setName("取款机一：");withdraw1.start();Thread withdraw2 = new Thread(new Withdraw2(account));withdraw2.setName("取款机二：");withdraw2.start();}}//存钱的线程类
class Deposit2 implements Runnable {private Account account;public Deposit2(Account account) {this.account = account;}public Account getAccount() {return account;}@Overridepublic void run() {for (int i = 0; i < 5; i++) {synchronized (account) {         //互斥锁，同步锁int add = (int) (Math.random() * 100);account.setBalance(account.getBalance() + add);System.out.println(Thread.currentThread().getName() + "存钱" + add + ", 当前账号余额为：" + account.getBalance());}try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}}}
}//取钱的线程类
class Withdraw2 implements Runnable {private Account account;public Account getAccount() {return account;}public Withdraw2(Account account) {this.account = account;}@Overridepublic void run() {for (int i = 0; i < 5; i++) {int money = (int) (Math.random() * 100);synchronized (account) {if (money > account.getBalance()) {System.out.println("余额不足，当前余额为：" + account.getBalance()+", 想取钱"+money);} else {account.setBalance(account.getBalance() - money);System.out.println(Thread.currentThread().getName() + "取钱" + money + ", 当前账号余额为：" + account.getBalance());}}try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}}}
}class Account {private String name;private int balance;public Account(String name, int balance) {this.name = name;this.balance = balance;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getBalance() {return balance;}public void setBalance(int balance) {this.balance = balance;}
}

wait()和notify()方法的使用

public class PrintRunnerTest {public static void main(String[] args) {Runnable runner = new PrintRunner();Thread thread1 = new Thread(runner);thread1.setName("线程1");Thread thread2 = new Thread(runner);thread2.setName("线程2");thread1.start();thread2.start();}
}public class PrintRunner implements Runnable {int n = 1;//使用两个线程打印 1-100. 线程1, 线程2 交替打印@Overridepublic void run() {for (int i = 0; i < 50; i++) {synchronized ("") {System.out.println(Thread.currentThread().getName() + " : " + n++);try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}"".notify();if (i < 49) {try {"".wait();} catch (InterruptedException e) {e.printStackTrace();}}}}}
}

/*** 银行有一个账户Account包含属性name, balance* 写一个普通 类Deposit实现Runnable, 在run方法中存钱* 有两个柜台(线程)分别同时向同一个账户存3000元，每次存1000，存3次。每次存完打印账户余额。睡眠10毫秒*/
public class Deposit implements Runnable {private Account account;public Deposit(Account account) {this.account = account;}@Overridepublic void run() {for (int i = 0; i < 3; i++) {synchronized ("") {account.setBalance(account.getBalance() + 1000);System.out.println(Thread.currentThread().getName() + " 存完钱后 : " + account);"".notify();}try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}}}
}

public class Withdraw implements Runnable {private Account account;public Withdraw(Account account) {this.account = account;}@Overridepublic void run() {// 取钱for (int i = 0; i < 3; i++) {synchronized ("") {if (account.getBalance() < 1000) {System.out.println("钱不够, 等待....");try {"".wait(); // 必须通过锁对象调用wait和nofity} catch (InterruptedException e) {e.printStackTrace();}}account.setBalance(account.getBalance() - 1000);System.out.println(Thread.currentThread().getName() + " 取完钱后 : " + account);try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}}}}
}

死锁

ublic class TestDeadLock {static StringBuilder s1 = new StringBuilder();static StringBuilder s2 = new StringBuilder();public static void main(String[] args) {new Thread() {public void run() {synchronized (s1) {s2.append("A");try {Thread.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}synchronized (s2) {         // synchronized (s1)代码不会造成死锁s2.append("B");System.out.print(s1);System.out.print(s2);}}}}.start();new Thread() {public void run() {synchronized (s2) {s2.append("C");synchronized (s1) {		// synchronized (s2)代码不会造成死锁s1.append("D");System.out.print(s2);System.out.print(s1);}}}}.start();}
}

网络编程

/*** TCP 传输控制协议*     C / S*     Server 是被动等待*     Client 是主动进攻* UDP 用户数据报*/

public class NetTest {@Testpublic void server() throws IOException {ServerSocket server = new ServerSocket(9999); // 在本机绑定9999portSocket socket1 = server.accept(); // 准备接受客户端的请求, 这个方法会阻塞System.out.println(socket1);BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket1.getInputStream()));String s = bufferedReader.readLine();System.out.println(s);bufferedReader.close(); // 关闭的顺序是从后向前socket1.close();server.close();}@Testpublic void client() throws IOException {Socket socket2 = new Socket("127.0.0.1", 9999);System.out.println(socket2);// 发送一个字符串BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket2.getOutputStream()));bufferedWriter.write("你好, 服务器, 我是客户端, 天气不错!!!");bufferedWriter.newLine(); // 必须要有换行, 不然网络对端无法readLinebufferedWriter.flush(); // 也是必须的, 保证数据写入网络bufferedWriter.close();socket2.close();}@Testpublic void test1() throws UnknownHostException {InetAddress byName = InetAddress.getByName("192.168.20.30");System.out.println(byName);System.out.println(byName.getHostName());}
}

// 服务器给客户端发送一段字符串, 再加上当前日期时间.
public class NetExer {//从客户端发送文件给服务端，服务端保存到本地。并返回“发送成功”给客户端。并关闭相应的连接。@Testpublic void server2() throws IOException {ServerSocket serverSocket = new ServerSocket(9876);Socket socket1 = serverSocket.accept();InputStream nis = socket1.getInputStream();FileOutputStream fos = new FileOutputStream("girl2.jpg");BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket1.getOutputStream()));byte[] buf = new byte[8192];int count;while ((count = nis.read(buf)) != -1) {fos.write(buf, 0, count);}bufferedWriter.write("发送成功!");bufferedWriter.newLine();bufferedWriter.flush();bufferedWriter.close();fos.close();nis.close();socket1.close();serverSocket.close();}@Testpublic void client2() throws IOException {Socket socket2 = new Socket("127.0.0.1", 9876);FileInputStream fis = new FileInputStream("girl.jpg"); // 文件输入流OutputStream nos = socket2.getOutputStream(); // 网络输出流BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket2.getInputStream()));byte[] buf = new byte[8192];int count;while ((count = fis.read(buf)) != -1) {nos.write(buf, 0, count);}socket2.shutdownOutput(); // 发送一个结束信号给服务器String s = bufferedReader.readLine();System.out.println(s);bufferedReader.close();nos.close();fis.close();socket2.close();}@Testpublic void server() throws IOException {ServerSocket server = new ServerSocket(7777);while (true) {System.out.println("服务器在端点7777监听....");Socket socket1 = server.accept();Runnable runnable = new Runnable() {public void run() {try {BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket1.getOutputStream()));bw.write("你好, 客户端 , 我是服务器, 当前时间 : " + LocalDateTime.now());bw.newLine();bw.flush();bw.close();socket1.close();Thread.sleep(10 * 1000);} catch (Exception e) {e.printStackTrace();}}};new Thread(runnable).start();}//server.close();}@Testpublic void client() throws IOException {Socket socket2 = new Socket("localhost", 7777);BufferedReader br = new BufferedReader(new InputStreamReader(socket2.getInputStream()));String line = br.readLine();System.out.println(line);br.close();socket2.close();}

/*** URL 统一资源定位器* <传输协议>://<主机名>:<端口号>/<文件名>* 例如: http://192.168.1.100:8080/helloworld/index.jsp*/

public class URLTest {@Testpublic void test1() throws Exception {String url = "http://www.juredian.net/uploads/allimg/200701/1-200F1092QN25.jpg";URL url1 = new URL(url);InputStream inputStream = url1.openStream();byte[] buf = new byte[8192];FileOutputStream fos = new FileOutputStream("test.jpg");int count;while ((count = inputStream.read(buf)) != -1) {fos.write(buf, 0, count);}fos.close();inputStream.close();}
}