java 编程思想中的PriorityBlockingQueue 部分里对PrioritizedTask的排序没有显式调用collection的sort方法。而是通过take时做的这个动作

最新推荐文章于 2025-02-18 21:51:11 发布

有毒的苹果

最新推荐文章于 2025-02-18 21:51:11 发布

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本文链接：https://blog.youkuaiyun.com/aq23es/article/details/51279432

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本文详细解析了PriorityBlockingQueue在take方法中如何通过compareTo方法自动排序，并解释了为何不需要调用Collections.sort方法。

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java 编程思想中的PriorityBlockingQueue 在take是会调用comparable 的compareTo进行排序，故不需要显式调用collection的sort方法

这个方法是PriorityBlockingQueue的：

public E take() throws InterruptedException {
    ReentrantLock localReentrantLock = this.lock;
    localReentrantLock.lockInterruptibly();
    try {
      try {
        while (this.q.size() == 0)
          this.notEmpty.await();
      } catch (InterruptedException localInterruptedException) {
        this.notEmpty.signal();
        throw localInterruptedException;
      }
      Object localObject1 = this.q.poll();//调用了poll方法并对poll进行了判空，这个poll是PriorityQueue的poll
      assert (localObject1 != null);
      return localObject1;
    } finally {
      localReentrantLock.unlock();
    }
  }

PriorityQueue的poll方法：

public E poll() {
    if (this.size == 0)
      return null;
    int i = --this.size;
    this.modCount += 1;
    Object localObject1 = this.queue[0];
    Object localObject2 = this.queue[i];
    this.queue[i] = null;
    if (i != 0)
      siftDown(0, localObject2);//调用了内部的siftDown进行排序
    return localObject1;
  }


private void siftDown(int paramInt, E paramE)
  {
    if (this.comparator != null)
      siftDownUsingComparator(paramInt, paramE);
    else
      siftDownComparable(paramInt, paramE);//java编程思想用的是comparable.
  }


private void siftDownComparable(int paramInt, E paramE) {
    Comparable localComparable = (Comparable)paramE;
    int i = this.size >>> 1;
    while (paramInt < i) {
      int j = (paramInt << 1) + 1;
      Object localObject = this.queue[j];
      int k = j + 1;
      if ((k < this.size) && (((Comparable)localObject).compareTo(this.queue[k]) > 0))
      {
        localObject = this.queue[(j = k)];
      }if (localComparable.compareTo(localObject) <= 0)//调用了添加到PriorityBlockingQueue的元素的compareTo方法，java编程思想是重写了comparable的compareTo
        break;
      this.queue[paramInt] = localObject;
      paramInt = j;
    }
    this.queue[paramInt] = localComparable;
  }

java 编程思想的PrioritizedTask继承并重写了compareTo，详情请参考java编程思想4版728页。所以在本书中得到例子并没有调用Collections.sort(list).

至此我个人的疑惑