优先级高优先

在运行多任务时，有多种选择策略，其中一种是优先级高优先，java可以通过PriorityBlockingQueue来实现。
代码例子：

//优先运行任务class PrioritizedTask implementsRunnable, Comparable<PrioritizedTask>  {  private Random rand = new Random(47);  private static int counter = 0;  private final int id = counter++;  private final int priority;  protected static List<PrioritizedTask> sequence =    new ArrayList<PrioritizedTask>();  public PrioritizedTask(int priority) {    this.priority = priority;    sequence.add(this);  }  //优先级比较  public int compareTo(PrioritizedTask arg) {    return priority < arg.priority ? 1 :      (priority > arg.priority ? -1 : 0);  }  public void run() {    try {      TimeUnit.MILLISECONDS.sleep(rand.nextInt(250));    } catch(InterruptedException e) {      // Acceptable way to exit    }    System.out.println(this);  }  public String toString() {    return String.format("[%1$-3d]", priority) +      " Task " + id;  }  public String summary() {    return "(" + id + ":" + priority + ")";  }  //终止任务的终止类  public static class EndSentinel extends PrioritizedTask {    private ExecutorService exec;    public EndSentinel(ExecutorService e) {      super(-1); // Lowest priority in this program      exec = e;    }    public void run() {      int count = 0;      System.out.println(this + " Calling shutdownNow()");      exec.shutdownNow();    }  }}//优先队列存储class PrioritizedTaskProducer implements Runnable {  private Random rand = new Random(47);  private Queue<Runnable> queue;  private ExecutorService exec;  public PrioritizedTaskProducer(    Queue<Runnable> q, ExecutorService e) {    queue = q;    exec = e;   }  public void run() {    for(int i = 0; i < 20; i++) {      queue.add(new PrioritizedTask(rand.nextInt(10)));      Thread.yield();    }    try {      for(int i = 0; i < 10; i++) {        TimeUnit.MILLISECONDS.sleep(250);        queue.add(new PrioritizedTask(10));      }      for(int i = 0; i < 10; i++)        queue.add(new PrioritizedTask(i));      // 终止所有任务      queue.add(new PrioritizedTask.EndSentinel(exec));    } catch(InterruptedException e) {    }    System.out.println("Finished PrioritizedTaskProducer");  }}//优先任务测试class PrioritizedTaskConsumer implements Runnable {  private PriorityBlockingQueue<Runnable> q;  public PrioritizedTaskConsumer(    PriorityBlockingQueue<Runnable> q) {    this.q = q;  }  public void run() {    try {      while(!Thread.interrupted())        // 用这个线程执行任务        q.take().run();    } catch(InterruptedException e) {    }    System.out.println("Finished PrioritizedTaskConsumer");  }}public class PriorityBlockingQueueDemo {  public static void main(String[] args) throws Exception {    Random rand = new Random(47);    ExecutorService exec = Executors.newCachedThreadPool();    PriorityBlockingQueue<Runnable> queue =      new PriorityBlockingQueue<Runnable>();    exec.execute(new PrioritizedTaskProducer(queue, exec));    exec.execute(new PrioritizedTaskConsumer(queue));  }}  

运行结果：
[8 ] Task 0
[9 ] Task 5
[9 ] Task 13
[9 ] Task 14
[8 ] Task 10
[8 ] Task 16
[8 ] Task 19
[8 ] Task 11
[8 ] Task 6
[8 ] Task 15
[7 ] Task 9
[5 ] Task 1
[3 ] Task 2
[2 ] Task 8
[1 ] Task 3
[1 ] Task 4
[1 ] Task 17
[1 ] Task 12
[0 ] Task 18
[0 ] Task 7
[10 ] Task 20
[10 ] Task 21
[10 ] Task 22
[10 ] Task 23
[10 ] Task 24
[10 ] Task 25
[10 ] Task 26
[10 ] Task 27
[10 ] Task 28
Finished PrioritizedTaskProducer
[10 ] Task 29
[9 ] Task 39
[8 ] Task 38
[7 ] Task 37
[6 ] Task 36
[5 ] Task 35
[4 ] Task 34
[3 ] Task 33
[2 ] Task 32
[1 ] Task 31
[0 ] Task 30
[-1 ] Task 40 Calling shutdownNow()
Finished PrioritizedTaskConsumer