41.线程

1.进程

 

 2.线程

 例如记事本:我们在打开记事本的时候打开页面设置:

 

 上面这种情况说明记事本整个执行流程只有一条执行路径,是单线程程序

再例如QQ:

 上面QQ的聊天界面和好友搜索界面有各自的执行路径,说明QQ是多线程程序

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3.多线程实现方式

方式1:

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i=0;i<=100;i++){
            System.out.println(i);
        }

    }
}

public class ThreadTest {
    public static void main(String[] args) {
        MyThread thread1 = new MyThread();
        MyThread thread2 = new MyThread();
//        thread1.run();//并没有启动线程,和普通方法调用一样
//        thread2.run();
//        void start​() 导致此线程开始执行; Java虚拟机调用此线程的run方法。
        thread1.start();
        thread2.start();
    }
}

方式2:

//定义一个类实现Runnable接口
public class MyRunable implements Runnable{
//    重写run方法
    @Override
    public void run() {
        for(int i=0;i<100;i++){
            System.out.println(Thread.currentThread().getName()+":"+i);
        }
    }
}

    public static void main(String[] args) {
//        创建MyRunable对象
        MyRunable myRunable = new MyRunable();
//        创建Thread对象并将myRunable对象作为Thread构造方法参数传递
        Thread thread1 = new Thread(myRunable, "火车票");
        Thread thread2 = new Thread(myRunable, "飞机票");
        thread1.start();
        thread2.start();
    }

4.设置和获取线程名称

获取默认线程名称

结果:Thread-n....

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i=0;i<=100;i++){
            System.out.println(getName()+":"+i);
        }
    }
    /**
     * public class Thread implements Runnable {
     *private volatile String name;
     *public Thread() {
     *         init(null, null, "Thread-" + nextThreadNum(), 0);
     *     }
     *private void init(ThreadGroup g, Runnable target, String name,long stackSize) {
     *         init(g, target, name, stackSize, null, true);
     *     }
     *private void init(ThreadGroup g, Runnable target, String name,long stackSize, AccessControlContext acc, boolean inheritThreadLocals) {
     *        this.name = name;
     *        }
     * private static int threadInitNumber;0,1,2...
     *private static synchronized int nextThreadNum() {
     *         return threadInitNumber++;//先return后++,所以依次返回0,1,2...
     *     }
     *
     * public final String getName() {
     *         return name;
     *     }
     *     }
     */
}

 设置线程名称

        thread1.setName("高铁");
        thread2.setName("飞机");

 帯参构造方法设置线程名称:

1.线程类要添加帯参构造方法,默认调用父类帯参构造方法

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i=0;i<=100;i++){
            System.out.println(getName()+":"+i);
        }
    }

    public MyThread() {
        
    }

    public MyThread(String name) {
        super(name);
    }
}

        MyThread myThread = new MyThread("线程1");

获取当前类线程名称

//static Thread currentThread​() 返回对当前正在执行的线程对象的引用。
        System.out.println(Thread.currentThread().getName());

5.线程调度(线程优先级)

//        IllegalArgumentException - 如果优先级不在 MIN_PRIORITY到 MAX_PRIORITY范围内。
//        thread1.setPriority(10000);//IllegalArgumentException:抛出表示一种方法已经通过了非法或不正确的参数。
//        从下面我们可以得知线程优先级的设置范围在1~10之间,并且默认值是5
        System.out.println(Thread.MAX_PRIORITY);//10
        System.out.println(Thread.MIN_PRIORITY);//1
        System.out.println(Thread.NORM_PRIORITY);//5
//        设置优先级
        thread1.setPriority(1);
        thread2.setPriority(5);
        thread3.setPriority(10);
        thread1.start();
        thread2.start();
        thread3.start();

6.线程控制

 sleep

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i=0;i<=100;i++){
            System.out.println(getName()+":"+i);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public static void main(String[] args) {
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();
        MyThread t3 = new MyThread();

        t1.setName("飞机");
        t2.setName("火车");
        t3.setName("汽车");

        t1.start();
        t2.start();
        t3.start();
    }

 每个线程执行一下之后都会"等待"一秒钟,所以大家执行的很均匀

join

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i=0;i<=100;i++){
            System.out.println(getName()+":"+i);
        }
    }
}

public static void main(String[] args) throws InterruptedException {
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();
        MyThread t3 = new MyThread();

        t1.setName("皇上");
        t2.setName("三皇子");
        t3.setName("六皇子");
//皇上死了之后三皇子和六皇子才 开始争夺"皇位(CPU)"
        t1.start();
        t1.join();
        t2.start();
        t3.start();
    }

 SetDaemon()

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i=0;i<=100;i++){
            System.out.println(getName()+":"+i);
        }
    }
}

    public static void main(String[] args) throws InterruptedException {
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();
        MyThread t3 = new MyThread();
        t1.setName("悟空");
        t2.setName("八戒");
        t3.setName("老沙");
//        悟空,八戒,沙僧,都是守护师傅的,那么如果师傅"死掉了(线程结束)",他们三个也没有存在的必要了,也应该停止
//        这里我们将上面三个线程设置为守护线程,当运行的线程都是守护线程时.java虚拟机将退出:
        t1.setDaemon(true);
        t2.setDaemon(true);
        t3.setDaemon(true);
        t1.start();
        t2.start();
        t3.start();
        Thread.currentThread().setName("师傅");
        for (int i=0;i<5;i++){
            System.out.println( Thread.currentThread().getName()+":"+i);
            Thread.currentThread().sleep(1);
        }
    }

 7.线程声明周期

8.线程同步

卖票案例

//定义一个类实现Runnable接口并重写run方法
public class SellTicket implements Runnable {
    //    定一个票数变量
    private int tickets = 100;

    @Override
    public void run() {
//        相同的票卖出了多次???卖负数票???
        while (true) {//定义死循环,一直卖票
            //        判断票数是否为0
//            假设thread1抢到了CPU执行权
            if (tickets > 0) {
                try {//通过sleep模拟卖出每张票所需要的时间
                    Thread.sleep(100);
//                    thread1休息100毫秒
//                    此时thread2抢到了CPU执行权,thread2开始执行,执行到这里thread2也休息100毫秒
//                    此时thread3抢到了CPU执行权,thread3开始执行,执行到这里thread3也休息100毫秒
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
//                假设线程按照顺序醒过来
//                thread1抢到了CPU执行权,在控制台输出:窗口1正在出售第100张票
                System.out.println(Thread.currentThread().getName() + ":正在卖第" + tickets + "张票");
//                 thread2抢到了CPU执行权,在控制台输出:窗口2正在出售第100张票
//                 thread3抢到了CPU执行权,在控制台输出:窗口3正在出售第100张票
                tickets--;
//                如果三个线程还是按照上面的顺序来,这次就执行了3次"--"的操作,tickets变成了97,,,最终同理就出现了卖"负数票"
            }
        }
    }

//        创建卖票窗口对象
        SellTicket sellTicket = new SellTicket();
//        创建三个线程对应三个卖票窗口
        Thread thread1 = new Thread(sellTicket, "窗口1");
        Thread thread2 = new Thread(sellTicket, "窗口2");
        Thread thread3 = new Thread(sellTicket, "窗口3");
        thread1.start();
        thread2.start();
        thread3.start();
    }

卖票结果:

 

卖票案例问题解决

 同步代码块:

public class SellTicket implements Runnable {
    private int tickets = 100;
    private Object o=new Object();//这里定义一个任意Object对象,保证是同一把锁
    @Override
    public void run() {
        while (true) {
//            thread1抢到了CPU执行权
            synchronized (o){
                if (tickets > 0) {
                    try {
//                    thread1进来之后就会把代码锁起来
                        Thread.sleep(100);
//                    thread1休息100毫秒
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
//                    thread1抢到了CPU执行权,在控制台输出:窗口1正在出售第100张票
                    System.out.println(Thread.currentThread().getName() + ":正在卖第" + tickets + "张票");
                    tickets--;
                }
//                    thread1出来之后解锁上面代码
            }
        }
    }
}

同步方法:

public class SellTicket implements Runnable {
    private static int tickets = 100;
    private Object o=new Object();
    private int X=0;
    @Override
    public void run() {
        while (true) {
            if(X%2==0){
//                synchronized (o){
//                synchronized (this){
                synchronized (SellTicket.class){
                    if (tickets > 0) {
                        try {
                            Thread.sleep(100);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName() + ":正在卖第" + tickets + "张票");
                        tickets--;
                    }
                }
            }else{
                sellTicket();
            }
            X++;
        }
    }

//    private synchronized void sellTicket() {
//            if (tickets > 0) {
//                try {
//                    Thread.sleep(100);
//                } catch (InterruptedException e) {
//                    e.printStackTrace();
//                }
//                System.out.println(Thread.currentThread().getName() + ":正在卖第" + tickets + "张票");
//                tickets--;
//            }
//    }
    private static synchronized void sellTicket() {
            if (tickets > 0) {
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + ":正在卖第" + tickets + "张票");
                tickets--;
            }
    }

}

9.线程安全的类

        StringBuffer stringBuffer = new StringBuffer();//线程安全,多线程情况下使用
        StringBuilder stringBuilder = new StringBuilder();//线程不安全,非多线程情况使用
        Vector<Object> vector = new Vector<>();//线程安全,多线程情况下使用
        ArrayList<Object> list = new ArrayList<>();//线程不安全,非多线程情况使用
        Hashtable<Object, Object> hashtable = new Hashtable<>();//线程安全,多线程情况下使用
        HashMap<Object, Object> hashMap = new HashMap<>();//线程不安全,非多线程情况使用
//        集合的安全类被下面的方法替代了
//        static <T> List<T> synchronizedList​(List<T> list) 返回由指定列表支持的同步（线程安全）列表。
        List<Object> synchronizedList = Collections.synchronizedList(list);
        Map<Object, Object> synchronizedMap = Collections.synchronizedMap(hashMap);

10.Lock

public class LockTest implements Runnable {
    private  int tickets = 100;
    private Lock lock=new ReentrantLock();
    @Override
    public void run() {
        while (true) {
            try {
                lock.lock();
                if (tickets > 0) {
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + ":正在卖第" + tickets + "张票");
                    tickets--;
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally { //无论什么情况下都要释放锁
                lock.unlock();
            }
        }
    }
}