Java多线程算法总结

1. 标题三个线程同时运行，依次打印ABC，一共打印10次

index.php/tags-41973.html" >���法代码如下：

public class ThreadTest {    private Object oa = new Object();    private Object ob = new Object();    private Object oc = new Object();    private static final String TAG = "ThreadTest";    private Runnable a = new Runnable() {        @Override        public void run() {            int count  = 10;            while (count > 0) {                synchronized (oc) {  //首先需要等待上个线程执行打印后，才能执行自己线程的打印任务。因此要获取到上个对象锁，这里是oc，并且执行oc.wait()方法                    //这样一旦在C线程中，oc执行了notify()方法后，才能按顺序让A线程继续执行                    synchronized (oa) { // 为了唤醒下一个B线程，执行oa.notify()方法，那么就需要对oa加锁                        Log.i(TAG, "A");                        count --;                        oa.notify();                    }                    try {                        oc.wait();                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                }            }        }    };    private Runnable b = new Runnable() {        @Override        public void run() {            int count  = 10;            while (count > 0) {                synchronized (oa) {                    synchronized (ob) {                        Log.i(TAG, "B");                        count --;                        ob.notify();                    }                    try {                        oa.wait();                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                }            }        }    };    private Runnable c = new Runnable() {        @Override        public void run() {            int count  = 10;            while (count > 0) {                synchronized (ob) {                    synchronized (oc) {                        Log.i(TAG, "C");                        count --;                        oc.notify();                    }                    try {                        ob.wait();                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                }            }        }    };    public void startThread() {        Thread at = new Thread(a);        Thread bt = new Thread(b);        Thread ct = new Thread(c);        try {            at.start();            Thread.sleep(100);  //保证第一次循环是ABC的顺序            bt.start();            Thread.sleep(100);            ct.start();        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

也可以把重复的Runnable抽象成一个，如下：

    private static class PrintRunnable implements Runnable {        Object prev;        Object current;        String name;        PrintRunnable(String name, Object prev, Object current) {            this.name = name;            this.prev = prev;            this.current = current;        }        @Override        public void run() {            int count = 10;            while (count > 0) {                synchronized (prev) {                    synchronized (current) {                        Log.i(TAG, name);                        count --;                        current.notify();                    }                    try {                        prev.wait();                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                }            }        }    }    public void startThread2() {        Thread ta = new Thread(new PrintRunnable("A", oc, oa));        Thread tb = new Thread(new PrintRunnable("B", oa, ob));        Thread tc = new Thread(new PrintRunnable("C", ob, oc));        try {            ta.start();            Thread.sleep(100);            tb.start();            Thread.sleep(100);            tc.start();        } catch (InterruptedException e) {            e.printStackTrace();        }    }

wait()会释放对象锁；notify()是起到唤醒等待对象锁的线程的作用，并不会马上释放锁，但是一旦同步代码块执行完毕后，就会释放对象锁。

2.生产者-消费者问题

代码如下：

 /**     * 生产者消费者问题     */    private static final int MAX_COUNT = 10;    List product = new LinkedList();    // 生产者    private Runnable build = new Runnable() {        @Override        public void run() {            while (true) {                synchronized (product) {                    while (product.size() >= MAX_COUNT) {                        // 如果商品已经达到最大存储量，则暂时不生产                        try {                            Log.i(TAG, Thread.currentThread().getName() + " 仓库已满");                            product.wait();                        } catch (InterruptedException e) {                            e.printStackTrace();                        }                    }                    product.add("商品");                    Log.i(TAG, Thread.currentThread().getName() + " 生产一个商品，当前商品存储量：" + product.size());                    product.notifyAll(); // 唤醒等待商品的消费者                }                try {                    Thread.sleep(2000);                } catch (InterruptedException e) {                    e.printStackTrace();                }            }        }    };    // 消费者    private Runnable consume = new Runnable() {        @Override        public void run() {            while (true) {                synchronized (product) {                    while (product.isEmpty()) {                        try {                            Log.i(TAG, Thread.currentThread().getName() + " 仓库已空");                            product.wait(); // 没有商品消费，等待生产                        } catch (InterruptedException e) {                            e.printStackTrace();                        }                    }                    product.remove(0);                    Log.i(TAG, Thread.currentThread().getName() + " 消费一个商品，当前商品存储量：" + product.size());                    product.notifyAll(); // 通知等待生产的生产者                }                try {                    Thread.sleep(4000);                } catch (InterruptedException e) {                    e.printStackTrace();                }            }        }    };    public void startThread3() {        Thread buildThread1 = new Thread(build);        Thread buildThread2 = new Thread(build);        Thread consumeThread1 = new Thread(consume);        Thread consumeThread2 = new Thread(consume);        Thread consumeThread3 = new Thread(consume);        buildThread1.start();        consumeThread1.start();        buildThread2.start();        consumeThread2.start();        consumeThread3.start();    }

打印如下：