线程 Thread Runnable Join

1.main是主线程，使用继承Thread的方法，无法多线程之间共享实例属性，因为每new一个Thread有自己的属性i，所以不共享。

class FirstThread extends Thread{private int i;//重写run方法public void run(){for(i=0; i<100; i++){System.out.println(getName() + " " +i);  //getName返回该线程的名字}}public static void main(String[] args) {for(int i=0; i<100; i++){System.out.println(Thread.currentThread().getName() + " " + i); //当前线程名字if(i==20){new FirstThread().start();  //创建启动第一条线程new FirstThread().start();  //创建启动第二条线程}}}}

输出：

---------- 运行Java程序 ----------
main 0
main 1
main 2
main 3
main 4
main 5
main 6
main 7
main 8
main 9
main 10
main 11
main 12
main 13
main 14
main 15
main 16
main 17
main 18
main 19
main 20
Thread-0 0
Thread-0 1
main 21
Thread-0 2
main 22
Thread-0 3
Thread-0 4
Thread-1 0
Thread-1 1
Thread-1 2
Thread-1 3
........省略

2.继承Runnable接口的方法实现线程，由于创建线程时时同一个target的st，所以线程之间共享i，是连续的

class SecondThread implements Runnable{private int i;public void run(){for(; i<100; i++){System.out.println(Thread.currentThread().getName() + " " + i);}}public static void main(String[] args) {for(int i=0; i<100; i++){System.out.println(Thread.currentThread().getName() + " " + i);if(i==20){SecondThread st = new SecondThread();//(Runnable target, String name) SeconThread是同一个target，共享inew Thread(st, "新线程1").start();  new Thread(st, "新线程2").start();}}}}

线程的生命周期

新建New

 就绪Runnable    start()以后处于就绪状态

运行running         执行run()方法时

阻塞Blocked         调用sleep等方法

 死亡Dead            run()方法执行完，异常，stop()等

控制线程 Join

main线程中调另一个线程jt.join()，main要等jt执行完毕才能执行

class JoinThread extends Thread {public JoinThread(String name){super(name);}public void run(){for(int i=0; i<100; i++){System.out.println(getName() + " " + i);}}public static void main(String[] args) throws Exception{new JoinThread("新线程").start();for(int i=0; i<100; i++){if(i==20){JoinThread jt = new JoinThread("被Join线程");jt.start();//main线程调用jt的join方法，所以main线程要等jt执行完毕后才能执行jt.join(); }System.out.println(Thread.currentThread().getName() + " " + i);}}}

后台线程

所有前台线程死亡后，后台线程就自动死亡，JVM的垃圾回收线程就是典型的后台线程

setDaemon必须在start之前设置

Thread t = new Thread();t.setDaemon(true);t.start();

线程睡眠

暂停一段时间

public void run(){for(int i=0; i<100; i++){System.out.println(getName() + " " + i);Thead.sleep(1000); //暂停1秒}}

线程的让步 

Thread.yield()优先级高的线程优先执行，高级执行完再执行低级，低级暂定

线程优先级设置

setPriority()

class ThreadYield extends Thread{private int i;ThreadYield(String name){super(name);}public void run(){for(; i<100; i++){System.out.println(getName() + " " + i);if(i==0){Thread.yield();}}}public static void main(String[] args) {ThreadYield ty1 = new ThreadYield("高级");//ty1.setPriority(Thread.MAX_PRIORITY);ty1.start();ThreadYield ty2 = new ThreadYield("低级");//ty2.setPriority(Thread.MIN_PRIORITY);ty2.start();}}

线程的同步

不同时，num的值小于0了，还能继续计算，导致出错

class ThreadSafe implements Runnable{int num = 10;public void run(){for(int i=0; i<20; i++){if(num>0){try{Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}System.out.println("tickets:" + num--);}}}public static void main(String[] args) {ThreadSafe t = new ThreadSafe();Thread A = new Thread(t);Thread B = new Thread(t);Thread C = new Thread(t);Thread D = new Thread(t);A.start();B.start();C.start();D.start();}}

---------- 运行Java程序 ----------
tickets:10
tickets:10
tickets:8
tickets:9
tickets:7
tickets:5
tickets:6
tickets:7
tickets:4
tickets:3
tickets:4
tickets:2
tickets:1
tickets:0
tickets:1
tickets:-1


输出完成 (耗时 4 秒) - 正常终止

同步代码块

synchronized(Object){ }   Object为任意代码块，标识位为0正在其他线程运行，1处于就绪状态

class ThreadSafe implements Runnable{int num = 10;public void run(){synchronized(""){for(int i=0; i<20; i++){if(num>0){try{Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}System.out.println("tickets:" + num--);}}}}public static void main(String[] args) {ThreadSafe t = new ThreadSafe();Thread A = new Thread(t);Thread B = new Thread(t);Thread C = new Thread(t);Thread D = new Thread(t);A.start();B.start();C.start();D.start();}}

---------- 运行Java程序 ----------
tickets:10
tickets:9
tickets:8
tickets:7
tickets:6
tickets:5
tickets:4
tickets:3
tickets:2
tickets:1


输出完成 (耗时 10 秒) - 正常终止

同步方法

run方法不能设置为同步方法

class ThreadSafe implements Runnable{int num = 10;public void run(){doit();}public synchronized void doit(){for(int i=0; i<20; i++){if(num>0){try{Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}System.out.println("tickets:" + num--);}}}public static void main(String[] args) {ThreadSafe t = new ThreadSafe();Thread A = new Thread(t);Thread B = new Thread(t);Thread C = new Thread(t);Thread D = new Thread(t);A.start();B.start();C.start();D.start();}}

---------- 运行Java程序 ----------
tickets:10
tickets:9
tickets:8
tickets:7
tickets:6
tickets:5
tickets:4
tickets:3
tickets:2
tickets:1


输出完成 (耗时 10 秒) - 正常终止

同步锁 Lock

ReentrantLock类，lock()和unlock()方法

import java.util.concurrent.locks.ReentrantLock;class ThreadSafe implements Runnable{private final ReentrantLock lock = new ReentrantLock();int num = 10;public void run(){lock.lock();try{for(int i=0; i<20; i++){if(num>0){try{Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}System.out.println("tickets:" + num--);}}}finally{lock.unlock();}}public static void main(String[] args) {ThreadSafe t = new ThreadSafe();Thread A = new Thread(t);Thread B = new Thread(t);Thread C = new Thread(t);Thread D = new Thread(t);A.start();B.start();C.start();D.start();}}

---------- 运行Java程序 ----------
tickets:10
tickets:9
tickets:8
tickets:7
tickets:6
tickets:5
tickets:4
tickets:3
tickets:2
tickets:1


输出完成 (耗时 10 秒) - 正常终止