java优先队列PriorityQueue中Comparator的用法详解

PriorityQueue<Integer> queue = new PriorityQueue<Integer>(new Comparator<Integer>(){
 @Override
 public int compare(Integer o1, Integer o2){
 return o1.compareTo(o2);
 }
});

public boolean offer(E e) {
    if (e == null) {
      throw new NullPointerException();
    } else {
      ++this.modCount;
      int i = this.size;
      if (i >= this.queue.length) {
        this.grow(i + 1);
      }

      this.siftUp(i, e);
      this.size = i + 1;
      return true;
    }
  }

private void siftUp(int k, E x) {
    if (this.comparator != null) {
      siftUpUsingComparator(k, x, this.queue, this.comparator);
    } else {
      siftUpComparable(k, x, this.queue);
    }

  }

private static <T> void siftUpUsingComparator(int k, T x, Object[] es, Comparator<? super T> cmp) {
    while(true) {
      if (k > 0) {
        int parent = k - 1 >>> 1;
        Object e = es[parent];
        if (cmp.compare(x, e) < 0) {
          es[k] = e;
          k = parent;
          continue;
        }
      }

      es[k] = x;
      return;
    }
  }

//对于最大堆，当x>e时，让x上升，则 x>e时返回负数，即
int compare(Integer x, Integer e){
 return x > e ? -1 : 1;
}
//对于最小堆，当x<e时，让compare(x, e) < 0，即
int compare(Integer x, Integer e){
 return x < e ? -1 : 1; // return x.compareTo(e);
}

// 最小优先队列，直接 return o1.compareTo(o2);
PriorityQueue<Integer> queue = new PriorityQueue<Integer>(new Comparator<Integer>(){
 @Override
 public int compare(Integer o1, Integer o2){
 return o1 < o2 ? -1 : 1;
 /* e.g., return o1.compare(o2); */
 }
});
// 最大优先队列，则反过来 return o2.compareTo(o1);