PriorityQueue.java

public class PriorityQueue<E> extends AbstractQueue<E>
    implements java.io.Serializable {

    private static final long serialVersionUID = -7720805057305804111L;
    private static final int DEFAULT_INITIAL_CAPACITY = 11;
    private transient Object[] queue;
    private int size = 0;
    private final Comparator<? super E> comparator;
    private transient int modCount = 0;
    public PriorityQueue() 
    public PriorityQueue(int initialCapacity) 
    public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) 
    public PriorityQueue(Collection<? extends E> c) 
    public PriorityQueue(SortedSet<? extends E> c) 
    private void initFromPriorityQueue(PriorityQueue<? extends E> c) 
    private void initElementsFromCollection(Collection<? extends E> c) 

    private void initFromCollection(Collection<? extends E> c) {
        initElementsFromCollection(c);
        heapify();
    }
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
    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);
    }

    private static int hugeCapacity(int minCapacity) 
    
    public boolean add(E e) 
    public boolean offer(E e)  => grow之后调用siftup

    public E peek() 

    private int indexOf(Object o) 

    public boolean remove(Object o) 
    boolean removeEq(Object o) 
    public boolean contains(Object o) 

    public Object[] toArray() 

    public <T> T[] toArray(T[] a) 
    public Iterator<E> iterator() 
    private final class Itr implements Iterator<E> {
      ...
    }

    public int size() 
    public void clear() 
    public E poll() 
    private E removeAt(int i) 

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

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

    private void siftUpUsingComparator(int k, E x) {
        while (k > 0) {
            int parent = (k - 1) >>> 1;
            Object e = queue[parent];
            if (comparator.compare(x, (E) e) >= 0)
                break;
            queue[k] = e;
            k = parent;
        }
        queue[k] = x;
    }

    
    private void siftDown(int k, E x) 

    private void siftDownComparable(int k, E x) {
        Comparable<? super E> key = (Comparable<? super E>)x;
        int half = size >>> 1;        // loop while a non-leaf
        while (k < half) {
            int child = (k << 1) + 1; // assume left child is least
            Object c = queue[child];
            int right = child + 1;
            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 siftDownUsingComparator(int k, E x) {
        int half = size >>> 1;
        while (k < half) {
            int child = (k << 1) + 1;
            Object c = queue[child];
            int right = child + 1;
            if (right < size &&
                comparator.compare((E) c, (E) queue[right]) > 0)
                c = queue[child = right];
            if (comparator.compare(x, (E) c) <= 0)
                break;
            queue[k] = c;
            k = child;
        }
        queue[k] = x;
    }

    private void heapify() {
        for (int i = (size >>> 1) - 1; i >= 0; i--)
            siftDown(i, (E) queue[i]);
    }

    public Comparator<? super E> comparator() {
        return comparator;
    }