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）

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();
    }
}

 

 

 

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　

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();
    }
}

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;
            }
        }
    }

　　//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

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