1 陣列中增加元素，從底層上升 保證最小堆

private void fixUp(int k) {
    while (k > 1) {
        int j = k >> 1;
        if (queue[j].nextExecutionTime <= queue[k].nextExecutionTime)
            break;
        TimerTask tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
        k = j;
    }
}

1.5 刪除元素

/**
 * Remove the head task from the priority queue.
 */
void removeMin() {
    queue[1] = queue[size];
    queue[size--] = null;  // Drop extra reference to prevent memory leak
    fixDown(1);
}

2 陣列中減少元素 ，從上層下降保證最小堆

private void fixDown(int k) {
    int j;
    while ((j = k << 1) <= size 
 
&& j > 0) {
        if (j < size && //注意是小於 少一次運算
            queue[j].nextExecutionTime > queue[j+1].nextExecutionTime)
            j++; // j indexes smallest kid
        if (queue[k].nextExecutionTime <= queue[j].nextExecutionTime)
            break;
        TimerTask tmp = queue
 
[j];  queue[j] = queue[k]; queue[k] = tmp;
        k = j;
    }
}

3 整體堆排序  注意：為什麼從 size/2 開始？和logn的關係

void heapify() {
    for (int i = size/2; i >= 1; i--)
        fixDown(i);
}