设置线程优先级

优先级的高低只是说明线程执行频率的高低，并不会导致线程得不到执行，优先权不会导致死锁

示例：

public class SimplePriorities implements Runnable{
    /**
     * 倒计时变量
     */
    private int countDown=5;
    private volatile double d;
    /**
     * 优先等级
     */
    private int priority;
    public SimplePriorities(int priority){
        this.priority=priority;
    }

    /**
     * 获取自动生成的名称和倒计时数
     * @return
     */
    public String toString(){
        return Thread.currentThread()+":"+countDown;
    }
    @Override
    public void run() {
        /**
         *设置当前线程的优先级
         */
        Thread.currentThread().setPriority(priority);
        while (true){
            for(int i=1;i<100000;i++){
                d+=(Math.PI+Math.E)/(double)i;
                if(i%1000==0)
                    //让出当前线程
                    Thread.yield();
            }
            System.out.println(this);
            if(--countDown==0)
                return;
        }
    }
    public static void main(String[] args){
        //使用执行器管理Thread对象
        ExecutorService exec= Executors.newCachedThreadPool();
        for(int i=0;i<5;i++)
            //优先级最小
            exec.execute(new SimplePriorities(Thread.MIN_PRIORITY));
        //优先级最大
        exec.execute(new SimplePriorities(Thread.MAX_PRIORITY));
        exec.shutdown();
    }
}