priavte transient Object[] queue;
private int size = 0;

private void initElementsFromCollection(Collection<? extends E> c) {
  Object[] a = c.toArray();
  // If c.toArray incorrectly doesn't return Object[], copy it.
  if (a.getClass() != Object[].class)
    a = Arrays.copyOf(a, a.length, Object[].class);
  int len = a.length;
  if (len == 1 || this.comparator != null)
    for (int i = 0; i < len; i++)
      if (a[i] == null)
        throw new NullPointerException();
  this.queue = a;
  this.size = a.length;
}

private void siftDownComparable(int k, E x) {
  Comparable<? super E> key = (Comparable<? super E>)x;
  int half = size >>> 1;    // size/2是第一个叶子结点的下标
  //只要没到叶子节点
  while (k < half) {
    int child = (k << 1) + 1; // 左孩子
    Object c = queue[child];
    int right = child + 1;
    //找出左右孩子中小的那个
    if (right < size &&
      ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
      c = queue[child = right];
    if (key.compareTo((E) c) <= 0)
      break;
    queue[k] = c;
    k = child;
  }
  queue[k] = key;
}

private void siftUpComparable(int k, E x) {
  Comparable<? super E> key = (Comparable<? super E>) x;
  while (k > 0) {
    int parent = (k - 1) >>> 1;   //获取parent下标
    Object e = queue[parent];
    if (key.compareTo((E) e) >= 0)
      break;
    queue[k] = e;
    k = parent;
  }
  queue[k] = key;
}

private void initFromCollection(Collection<? extends E> c) {
    initElementsFromCollection(c);
    heapify();
  }

private void grow(int minCapacity) {
    int oldCapacity = queue.length;
    // Double size if small; else grow by 50%
    int newCapacity = oldCapacity + ((oldCapacity < 64) ?
                     (oldCapacity + 2) :
                     (oldCapacity >> 1));
    // overflow-conscious code
    if (newCapacity - MAX_ARRAY_SIZE > 0)
      newCapacity = hugeCapacity(minCapacity);
    queue = Arrays.copyOf(queue, newCapacity);
  }

  //data是动态数据
  //heap维持动态数据的堆
  //res用来保存第K大的值
  public boolean kthLargest(int data, int k, PriorityQueue<Integer> heap, int[] res) {
    if(heap.size() < k) {
      heap.offer(data);
      if(heap.size() == k) {
        res[0] = heap.peek();
        return true;
      }
      return false;
    }
    if(heap.peek() < data) {
      heap.poll();
      heap.offer(data);
    }
    res[0] = heap.peek();
    return true;
  }

package com.journaldev.collections;
 
public class Customer {
 
  private int id;
  private String name;
 
  public Customer(int i, String n){
    this.id=i;
    this.name=n;
  }
 
  public int getId() {
    return id;
  }
 
  public String getName() {
    return name;
  }
 
}

package com.journaldev.collections;
 
import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Random;
 
public class PriorityQueueExample {
 
  public static void main(String[] args) {
 
    //优先队列自然排序示例
    Queue<Integer> integerPriorityQueue = new PriorityQueue<>(7);
    Random rand = new Random();
    for(int i=0;i<7;i++){
      integerPriorityQueue.add(new Integer(rand.nextInt(100)));
    }
    for(int i=0;i<7;i++){
      Integer in = integerPriorityQueue.poll();
      System.out.println("Processing Integer:"+in);
    }
 
    //优先队列使用示例
    Queue<Customer> customerPriorityQueue = new PriorityQueue<>(7, idComparator);
    addDataToQueue(customerPriorityQueue);
 
    pollDataFromQueue(customerPriorityQueue);
 
  }
 
  //匿名Comparator实现
  public static Comparator<Customer> idComparator = new Comparator<Customer>(){
 
    @Override
    public int compare(Customer c1, Customer c2) {
      return (int) (c1.getId() - c2.getId());
    }
  };
 
  //用于往队列增加数据的通用方法
  private static void addDataToQueue(Queue<Customer> customerPriorityQueue) {
    Random rand = new Random();
    for(int i=0; i<7; i++){
      int id = rand.nextInt(100);
      customerPriorityQueue.add(new Customer(id, "Pankaj "+id));
    }
  }
 
  //用于从队列取数据的通用方法
  private static void pollDataFromQueue(Queue<Customer> customerPriorityQueue) {
    while(true){
      Customer cust = customerPriorityQueue.poll();
      if(cust == null) break;
      System.out.println("Processing Customer with ID="+cust.getId());
    }
  }
 
}

Processing Integer:9
Processing Integer:16
Processing Integer:18
Processing Integer:25
Processing Integer:33
Processing Integer:75
Processing Integer:77
Processing Customer with ID=6
Processing Customer with ID=20
Processing Customer with ID=24
Processing Customer with ID=28
Processing Customer with ID=29
Processing Customer with ID=82
Processing Customer with ID=96

Exception in thread "main" java.lang.ClassCastException: com.journaldev.collections.Customer cannot be cast to java.lang.Comparable
  at java.util.PriorityQueue.siftUpComparable(PriorityQueue.java:633)
  at java.util.PriorityQueue.siftUp(PriorityQueue.java:629)
  at java.util.PriorityQueue.offer(PriorityQueue.java:329)
  at java.util.PriorityQueue.add(PriorityQueue.java:306)
  at com.journaldev.collections.PriorityQueueExample.addDataToQueue(PriorityQueueExample.java:45)
  at com.journaldev.collections.PriorityQueueExample.main(PriorityQueueExample.java:25)