解决线程安全问题

方式一：同步代码块

synchronized (同步监视器){
//需要被同步的代码
}
说明：
操作共享数据的代码，即为需要被同步的代码
共享数据：多个线程共同操作的变量
同步监视器：俗称，锁。任何一个类的对象都可以充当锁。（要求：多个线程必须要共用同一把锁）

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public class Window implements Runnable {     private int ticket = 100;     private Object obj = new Object();       @Override     public void run() {         while (true) {             synchronized (obj) { //可以用this，此时的this：唯一的Window的对象                 if (ticket > 0) {                     try {                         Thread.sleep(100);                     } catch (InterruptedException e) {                         e.printStackTrace();                     }                     System.out.println(Thread.currentThread().getName() + "***" + ticket);                     ticket--;                 } else {                     break;                 }             }         }     } }   class WindowTest {     public static void main(String[] args) {         Window w = new Window();         Thread t1 = new Thread(w);//3个线程公用1个w对象         Thread t2 = new Thread(w);         Thread t3 = new Thread(w);           t1.setName("线程1");         t2.setName("线程2");         t3.setName("线程3");           t1.start();         t2.start();         t3.start();     } }

 

 

 

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public class ThreadTest {       public static void main(String[] args) {         Window1 t1 = new Window1();         Window1 t2 = new Window1();         Window1 t3 = new Window1();         t1.setName("线程1");         t2.setName("线程2");         t3.setName("线程3");           t1.start();         t2.start();         t3.start();     } }   class Window1 extends Thread{     private static int ticket = 100;     private static Object obj = new Object();       @Override     public void run() {         while (true) {             synchronized (obj) { //可以用Window1.class，类也是对象，在内存中只加载一次                 if (ticket > 0) {                     try {                         Thread.sleep(100);                     } catch (InterruptedException e) {                         e.printStackTrace();                     }                     System.out.println(Thread.currentThread().getName() + "***" + ticket);                     ticket--;                 } else {                     break;                 }             }         }     } }

　　

　方式二：同步方法

如果操作共享数据的代码完整的声明在一个方法中，我们不妨将此方法声明为同步的　

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public class Window implements Runnable {     private int ticket = 100;       @Override     public void run() {         while (true) {             sale();             if(ticket==0){                 return;             }         }     } 　　//方法中加synchronized关键字,同步监视器：this     public synchronized void sale(){         if (ticket > 0) {             try {                 Thread.sleep(100);             } catch (InterruptedException e) {                 e.printStackTrace();             }             System.out.println(Thread.currentThread().getName() + "***" + ticket);             ticket--;         }     } }   class WindowTest {     public static void main(String[] args) {         Window w = new Window();         Thread t1 = new Thread(w);         Thread t2 = new Thread(w);         Thread t3 = new Thread(w);           t1.setName("线程1");         t2.setName("线程2");         t3.setName("线程3");           t1.start();         t2.start();         t3.start();     } }

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public class ThreadTest {       public static void main(String[] args) {         Window1 t1 = new Window1();         Window1 t2 = new Window1();         Window1 t3 = new Window1();         t1.setName("线程1");         t2.setName("线程2");         t3.setName("线程3");           t1.start();         t2.start();         t3.start();     } }   class Window1 extends Thread {     private static int ticket = 100;       @Override     public void run() {         while (true) {             sale();             if (ticket == 0) {                 return;             }         }     } <br>　　//同步监视器：当前类本身Window1.class     public static synchronized void sale() {         if (ticket > 0) {             try {                 Thread.sleep(100);             } catch (InterruptedException e) {                 e.printStackTrace();             }             System.out.println(Thread.currentThread().getName() + "***" + ticket);             ticket--;         }     } }

　　

　　

方式三：lock锁----jdk5.0新增

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public class LockTest {     public static void main(String[] args) {         Window2 w2 = new Window2();         Thread t1 = new Thread(w2);         Thread t2 = new Thread(w2);         Thread t3 = new Thread(w2);           t1.setName("窗口1");         t2.setName("窗口2");         t3.setName("窗口3");           t1.start();         t2.start();         t3.start();     } }   class Window2 implements Runnable {     private int ticket = 100;     //1.实例化ReentrantLock     private ReentrantLock lock = new ReentrantLock();       @Override     public void run() {         while (true) {             try {                 //2.调用锁定方法lock()                 lock.lock();                 if(ticket > 0){                     try {                         Thread.sleep(100);                     } catch (InterruptedException e) {                         e.printStackTrace();                     }                     System.out.println(Thread.currentThread().getName()+"正在售票"+ticket);                     ticket--;                 }else {                     break;                 }             }finally{                 //3.调用解锁方法unlock()                 lock.unlock();             }         }     }   }

　　

synchronized和lock异同

相同：都可以解决线程安全问题
不同：synchronized机制在执行完相应的同步代码以后，自动释放锁。
　　　　lock需要手动的启动同步，同时结束同步也需要手动的释放