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/* |
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* Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved. |
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* Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Sun designates this |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Sun in the LICENSE file that accompanied this code. |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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*/ |
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package java.util; |
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import java.util.stream.Stream; |
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import java.util.Spliterator; |
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import java.util.stream.Streams; |
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import java.util.function.Block; |
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/** |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* the priority queue in any particular order. If you need ordered |
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* traversal, consider using {@code Arrays.sort(pq.toArray())}. |
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* |
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* <p> <strong>Note that this implementation is not synchronized.</strong> |
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* <p><strong>Note that this implementation is not synchronized.</strong> |
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* Multiple threads should not access a {@code PriorityQueue} |
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* instance concurrently if any of the threads modifies the queue. |
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* Instead, use the thread-safe {@link |
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* @author Josh Bloch, Doug Lea |
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* @param <E> the type of elements held in this collection |
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*/ |
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@SuppressWarnings("unchecked") |
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public class PriorityQueue<E> extends AbstractQueue<E> |
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implements java.io.Serializable { |
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|
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* heap and each descendant d of n, n <= d. The element with the |
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* lowest value is in queue[0], assuming the queue is nonempty. |
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*/ |
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private transient Object[] queue; |
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transient Object[] queue; // non-private to simplify nested class access |
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|
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/** |
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* The number of elements in the priority queue. |
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* The number of times this priority queue has been |
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* <i>structurally modified</i>. See AbstractList for gory details. |
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*/ |
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private transient int modCount = 0; |
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transient int modCount = 0; // non-private to simplify nested class access |
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|
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/** |
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* Creates a {@code PriorityQueue} with the default initial |
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return true; |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E peek() { |
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return (size == 0) ? null : (E) queue[0]; |
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} |
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* precise control over the runtime type of the output array, and may, |
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* under certain circumstances, be used to save allocation costs. |
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* |
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* <p>Suppose <tt>x</tt> is a queue known to contain only strings. |
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* <p>Suppose {@code x} is a queue known to contain only strings. |
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* The following code can be used to dump the queue into a newly |
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* allocated array of <tt>String</tt>: |
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* allocated array of {@code String}: |
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* |
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* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
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* |
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* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
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* <tt>toArray()</tt>. |
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* Note that {@code toArray(new Object[0])} is identical in function to |
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* {@code toArray()}. |
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* |
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* @param a the array into which the elements of the queue are to |
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* be stored, if it is big enough; otherwise, a new array of the |
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* this queue |
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* @throws NullPointerException if the specified array is null |
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*/ |
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@SuppressWarnings("unchecked") |
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public <T> T[] toArray(T[] a) { |
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final int size = this.size; |
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if (a.length < size) |
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// Make a new array of a's runtime type, but my contents: |
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return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
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(forgetMeNot != null && !forgetMeNot.isEmpty()); |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E next() { |
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if (expectedModCount != modCount) |
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throw new ConcurrentModificationException(); |
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size = 0; |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E poll() { |
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if (size == 0) |
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return null; |
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* position before i. This fact is used by iterator.remove so as to |
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* avoid missing traversing elements. |
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*/ |
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@SuppressWarnings("unchecked") |
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private E removeAt(int i) { |
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// assert i >= 0 && i < size; |
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modCount++; |
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siftUpComparable(k, x); |
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} |
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@SuppressWarnings("unchecked") |
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private void siftUpComparable(int k, E x) { |
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Comparable<? super E> key = (Comparable<? super E>) x; |
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while (k > 0) { |
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queue[k] = key; |
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} |
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@SuppressWarnings("unchecked") |
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private void siftUpUsingComparator(int k, E x) { |
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while (k > 0) { |
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int parent = (k - 1) >>> 1; |
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siftDownComparable(k, x); |
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} |
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@SuppressWarnings("unchecked") |
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private void siftDownComparable(int k, E x) { |
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Comparable<? super E> key = (Comparable<? super E>)x; |
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int half = size >>> 1; // loop while a non-leaf |
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queue[k] = key; |
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} |
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@SuppressWarnings("unchecked") |
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private void siftDownUsingComparator(int k, E x) { |
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int half = size >>> 1; |
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while (k < half) { |
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* Establishes the heap invariant (described above) in the entire tree, |
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* assuming nothing about the order of the elements prior to the call. |
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*/ |
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@SuppressWarnings("unchecked") |
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private void heapify() { |
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for (int i = (size >>> 1) - 1; i >= 0; i--) |
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siftDown(i, (E) queue[i]); |
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* @serialData The length of the array backing the instance is |
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* emitted (int), followed by all of its elements |
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* (each an {@code Object}) in the proper order. |
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* @param s the stream |
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*/ |
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private void writeObject(java.io.ObjectOutputStream s) |
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throws java.io.IOException { |
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} |
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/** |
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* Reconstitutes this queue from a stream (that is, deserializes it). |
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* Reconstitutes the {@code PriorityQueue} instance from a stream |
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* (that is, deserializes it). |
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* |
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* @param s the stream |
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*/ |
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private void readObject(java.io.ObjectInputStream s) |
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throws java.io.IOException, ClassNotFoundException { |
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// spec has never explained what that might be. |
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heapify(); |
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} |
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|
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// wrapping constructor in method avoids transient javac problems |
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final PriorityQueueSpliterator<E> spliterator(int origin, int fence, |
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int expectedModCount) { |
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return new PriorityQueueSpliterator<E>(this, origin, fence, |
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expectedModCount); |
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} |
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|
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public Stream<E> stream() { |
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int flags = Streams.STREAM_IS_SIZED; |
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return Streams.stream |
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(() -> spliterator(0, size, modCount), flags); |
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} |
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public Stream<E> parallelStream() { |
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int flags = Streams.STREAM_IS_SIZED; |
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return Streams.parallelStream |
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(() -> spliterator(0, size, modCount), flags); |
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} |
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|
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/** Index-based split-by-two Spliterator */ |
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static final class PriorityQueueSpliterator<E> |
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implements Spliterator<E>, Iterator<E> { |
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private final PriorityQueue<E> pq; |
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private int index; // current index, modified on advance/split |
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private final int fence; // one past last index |
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private final int expectedModCount; // for comodification checks |
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|
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/** Create new spliterator covering the given range */ |
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PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence, |
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int expectedModCount) { |
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this.pq = pq; this.index = origin; this.fence = fence; |
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this.expectedModCount = expectedModCount; |
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} |
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|
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public PriorityQueueSpliterator<E> trySplit() { |
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int lo = index, mid = (lo + fence) >>> 1; |
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return (lo >= mid) ? null : |
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new PriorityQueueSpliterator<E>(pq, lo, index = mid, |
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expectedModCount); |
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} |
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public void forEach(Block<? super E> block) { |
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Object[] a; int i, hi; // hoist accesses and checks from loop |
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if (block == null) |
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throw new NullPointerException(); |
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if ((a = pq.queue).length >= (hi = fence) && |
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(i = index) >= 0 && i < hi) { |
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index = hi; |
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do { |
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@SuppressWarnings("unchecked") E e = (E) a[i]; |
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block.accept(e); |
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} while (++i < hi); |
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if (pq.modCount != expectedModCount) |
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throw new ConcurrentModificationException(); |
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} |
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} |
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|
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public boolean tryAdvance(Block<? super E> block) { |
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if (index >= 0 && index < fence) { |
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if (pq.modCount != expectedModCount) |
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throw new ConcurrentModificationException(); |
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@SuppressWarnings("unchecked") E e = |
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(E)pq.queue[index++]; |
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block.accept(e); |
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return true; |
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} |
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return false; |
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} |
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|
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public long estimateSize() { return (long)(fence - index); } |
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public boolean hasExactSize() { return true; } |
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public boolean hasExactSplits() { return true; } |
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|
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// Iterator support |
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public Iterator<E> iterator() { return this; } |
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public void remove() { throw new UnsupportedOperationException(); } |
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public boolean hasNext() { return index >= 0 && index < fence; } |
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|
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public E next() { |
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if (index < 0 || index >= fence) |
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throw new NoSuchElementException(); |
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if (pq.modCount != expectedModCount) |
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throw new ConcurrentModificationException(); |
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@SuppressWarnings("unchecked") E e = |
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(E) pq.queue[index++]; |
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return e; |
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} |
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} |
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} |