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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections.buffer;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.BufferUnderflowException;
/**
* Binary heap implementation of Buffer that provides for
* removal based on Comparator ordering.
*
* The removal order of a binary heap is based on either the natural sort
* order of its elements or a specified {@link Comparator}. The
* {@link #remove()} method always returns the first element as determined
* by the sort order. (The ascendingOrder flag in the constructors
* can be used to reverse the sort order, in which case {@link #remove()}
* will always remove the last element.) The removal order is
* not the same as the order of iteration; elements are
* returned by the iterator in no particular order.
*
* The {@link #add(Object)} and {@link #remove()} operations perform
* in logarithmic time. The {@link #get()} operation performs in constant
* time. All other operations perform in linear time or worse.
*
* Note that this implementation is not synchronized. Use
* {@link org.apache.commons.collections.BufferUtils#synchronizedBuffer(Buffer)} or
* {@link org.apache.commons.collections.buffer.SynchronizedBuffer#decorate(Buffer)}
* to provide synchronized access to a PriorityBuffer:
*
* Buffer heap = SynchronizedBuffer.decorate(new PriorityBuffer());
*
*
* This class is Serializable from Commons Collections 3.2.
*
* @since Commons Collections 3.0 (previously BinaryHeap v1.0)
* @version $Revision$ $Date$
*
* @author Peter Donald
* @author Ram Chidambaram
* @author Michael A. Smith
* @author Paul Jack
* @author Stephen Colebourne
* @author Steve Phelps
*
* @deprecated Apache Commons Collections version 3.x is being deprecated from AEMaaCS. The upgraded version 4.4 of Commons Collections is already included as replacement. Customers are advised to upgrade to this version of the library. Please note: the package name was changed to org.apache.commons.collections4. Further note that there are AEM APIs currently exposing the old collections classes; these will be updated in upcoming releases.
*/
@Deprecated(since = "2021-04-30")
public class PriorityBuffer extends AbstractCollection implements Buffer, Serializable {
/**
* Serialization lock.
*/
private static final long serialVersionUID = 6891186490470027896L;
/**
* The default capacity for the buffer.
*/
private static final int DEFAULT_CAPACITY = 13;
/**
* The elements in this buffer.
*/
protected Object[] elements;
/**
* The number of elements currently in this buffer.
*/
protected int size;
/**
* If true, the first element as determined by the sort order will
* be returned. If false, the last element as determined by the
* sort order will be returned.
*/
protected boolean ascendingOrder;
/**
* The comparator used to order the elements
*/
protected Comparator comparator;
// -----------------------------------------------------------------------
/**
* Constructs a new empty buffer that sorts in ascending order by the
* natural order of the objects added.
*/
public PriorityBuffer() {
this(DEFAULT_CAPACITY, true, null);
}
/**
* Constructs a new empty buffer that sorts in ascending order using the
* specified comparator.
*
* @param comparator the comparator used to order the elements,
* null means use natural order
*/
public PriorityBuffer(Comparator comparator) {
this(DEFAULT_CAPACITY, true, comparator);
}
/**
* Constructs a new empty buffer specifying the sort order and using the
* natural order of the objects added.
*
* @param ascendingOrder if true the heap is created as a
* minimum heap; otherwise, the heap is created as a maximum heap
*/
public PriorityBuffer(boolean ascendingOrder) {
this(DEFAULT_CAPACITY, ascendingOrder, null);
}
/**
* Constructs a new empty buffer specifying the sort order and comparator.
*
* @param ascendingOrder true to use the order imposed by the given
* comparator; false to reverse that order
* @param comparator the comparator used to order the elements,
* null means use natural order
*/
public PriorityBuffer(boolean ascendingOrder, Comparator comparator) {
this(DEFAULT_CAPACITY, ascendingOrder, comparator);
}
/**
* Constructs a new empty buffer that sorts in ascending order by the
* natural order of the objects added, specifying an initial capacity.
*
* @param capacity the initial capacity for the buffer, greater than zero
* @throws IllegalArgumentException if capacity is <= 0
*/
public PriorityBuffer(int capacity) {
this(capacity, true, null);
}
/**
* Constructs a new empty buffer that sorts in ascending order using the
* specified comparator and initial capacity.
*
* @param capacity the initial capacity for the buffer, greater than zero
* @param comparator the comparator used to order the elements,
* null means use natural order
* @throws IllegalArgumentException if capacity is <= 0
*/
public PriorityBuffer(int capacity, Comparator comparator) {
this(capacity, true, comparator);
}
/**
* Constructs a new empty buffer that specifying initial capacity and
* sort order, using the natural order of the objects added.
*
* @param capacity the initial capacity for the buffer, greater than zero
* @param ascendingOrder if true the heap is created as a
* minimum heap; otherwise, the heap is created as a maximum heap.
* @throws IllegalArgumentException if capacity is <= 0
*/
public PriorityBuffer(int capacity, boolean ascendingOrder) {
this(capacity, ascendingOrder, null);
}
/**
* Constructs a new empty buffer that specifying initial capacity,
* sort order and comparator.
*
* @param capacity the initial capacity for the buffer, greater than zero
* @param ascendingOrder true to use the order imposed by the given
* comparator; false to reverse that order
* @param comparator the comparator used to order the elements,
* null means use natural order
* @throws IllegalArgumentException if capacity is <= 0
*/
public PriorityBuffer(int capacity, boolean ascendingOrder, Comparator comparator) {
super();
if (capacity <= 0) {
throw new IllegalArgumentException("invalid capacity");
}
this.ascendingOrder = ascendingOrder;
// +1 as 0 is noop
this.elements = new Object[capacity + 1];
this.comparator = comparator;
}
// -----------------------------------------------------------------------
/**
* Checks whether the heap is ascending or descending order.
*
* @return true if ascending order (a min heap)
*/
public boolean isAscendingOrder() {
return ascendingOrder;
}
/**
* Gets the comparator being used for this buffer, null is natural order.
*
* @return the comparator in use, null is natural order
*/
public Comparator comparator() {
return comparator;
}
// -----------------------------------------------------------------------
/**
* Returns the number of elements in this buffer.
*
* @return the number of elements in this buffer
*/
public int size() {
return size;
}
/**
* Clears all elements from the buffer.
*/
public void clear() {
// for gc
elements = new Object[elements.length];
size = 0;
}
/**
* Adds an element to the buffer.
*
* The element added will be sorted according to the comparator in use.
*
* @param element the element to be added
* @return true always
*/
public boolean add(Object element) {
if (isAtCapacity()) {
grow();
}
// percolate element to it's place in tree
if (ascendingOrder) {
percolateUpMinHeap(element);
} else {
percolateUpMaxHeap(element);
}
return true;
}
/**
* Gets the next element to be removed without actually removing it (peek).
*
* @return the next element
* @throws BufferUnderflowException if the buffer is empty
*/
public Object get() {
if (isEmpty()) {
throw new BufferUnderflowException();
} else {
return elements[1];
}
}
/**
* Gets and removes the next element (pop).
*
* @return the next element
* @throws BufferUnderflowException if the buffer is empty
*/
public Object remove() {
final Object result = get();
elements[1] = elements[size--];
// set the unused element to 'null' so that the garbage collector
// can free the object if not used anywhere else.(remove reference)
elements[size + 1] = null;
if (size != 0) {
// percolate top element to it's place in tree
if (ascendingOrder) {
percolateDownMinHeap(1);
} else {
percolateDownMaxHeap(1);
}
}
return result;
}
// -----------------------------------------------------------------------
/**
* Tests if the buffer is at capacity.
*
* @return true if buffer is full; false otherwise.
*/
protected boolean isAtCapacity() {
// +1 as element 0 is noop
return elements.length == size + 1;
}
/**
* Percolates element down heap from the position given by the index.
*
* Assumes it is a minimum heap.
*
* @param index the index for the element
*/
protected void percolateDownMinHeap(final int index) {
final Object element = elements[index];
int hole = index;
while ((hole * 2) <= size) {
int child = hole * 2;
// if we have a right child and that child can not be percolated
// up then move onto other child
if (child != size && compare(elements[child + 1], elements[child]) < 0) {
child++;
}
// if we found resting place of bubble then terminate search
if (compare(elements[child], element) >= 0) {
break;
}
elements[hole] = elements[child];
hole = child;
}
elements[hole] = element;
}
/**
* Percolates element down heap from the position given by the index.
*
* Assumes it is a maximum heap.
*
* @param index the index of the element
*/
protected void percolateDownMaxHeap(final int index) {
final Object element = elements[index];
int hole = index;
while ((hole * 2) <= size) {
int child = hole * 2;
// if we have a right child and that child can not be percolated
// up then move onto other child
if (child != size && compare(elements[child + 1], elements[child]) > 0) {
child++;
}
// if we found resting place of bubble then terminate search
if (compare(elements[child], element) <= 0) {
break;
}
elements[hole] = elements[child];
hole = child;
}
elements[hole] = element;
}
/**
* Percolates element up heap from the position given by the index.
*
* Assumes it is a minimum heap.
*
* @param index the index of the element to be percolated up
*/
protected void percolateUpMinHeap(final int index) {
int hole = index;
Object element = elements[hole];
while (hole > 1 && compare(element, elements[hole / 2]) < 0) {
// save element that is being pushed down
// as the element "bubble" is percolated up
final int next = hole / 2;
elements[hole] = elements[next];
hole = next;
}
elements[hole] = element;
}
/**
* Percolates a new element up heap from the bottom.
*
* Assumes it is a minimum heap.
*
* @param element the element
*/
protected void percolateUpMinHeap(final Object element) {
elements[++size] = element;
percolateUpMinHeap(size);
}
/**
* Percolates element up heap from from the position given by the index.
*
* Assume it is a maximum heap.
*
* @param index the index of the element to be percolated up
*/
protected void percolateUpMaxHeap(final int index) {
int hole = index;
Object element = elements[hole];
while (hole > 1 && compare(element, elements[hole / 2]) > 0) {
// save element that is being pushed down
// as the element "bubble" is percolated up
final int next = hole / 2;
elements[hole] = elements[next];
hole = next;
}
elements[hole] = element;
}
/**
* Percolates a new element up heap from the bottom.
*
* Assume it is a maximum heap.
*
* @param element the element
*/
protected void percolateUpMaxHeap(final Object element) {
elements[++size] = element;
percolateUpMaxHeap(size);
}
/**
* Compares two objects using the comparator if specified, or the
* natural order otherwise.
*
* @param a the first object
* @param b the second object
* @return -ve if a less than b, 0 if they are equal, +ve if a greater than b
*/
protected int compare(Object a, Object b) {
if (comparator != null) {
return comparator.compare(a, b);
} else {
return ((Comparable) a).compareTo(b);
}
}
/**
* Increases the size of the heap to support additional elements
*/
protected void grow() {
final Object[] array = new Object[elements.length * 2];
System.arraycopy(elements, 0, array, 0, elements.length);
elements = array;
}
// -----------------------------------------------------------------------
/**
* Returns an iterator over this heap's elements.
*
* @return an iterator over this heap's elements
*/
public Iterator iterator() {
return new Iterator() {
private int index = 1;
private int lastReturnedIndex = -1;
public boolean hasNext() {
return index <= size;
}
public Object next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
lastReturnedIndex = index;
index++;
return elements[lastReturnedIndex];
}
public void remove() {
if (lastReturnedIndex == -1) {
throw new IllegalStateException();
}
elements[lastReturnedIndex] = elements[size];
elements[size] = null;
size--;
if (size != 0 && lastReturnedIndex <= size) {
int compareToParent = 0;
if (lastReturnedIndex > 1) {
compareToParent = compare(elements[lastReturnedIndex], elements[lastReturnedIndex / 2]);
}
if (ascendingOrder) {
if (lastReturnedIndex > 1 && compareToParent < 0) {
percolateUpMinHeap(lastReturnedIndex);
} else {
percolateDownMinHeap(lastReturnedIndex);
}
} else {
// max heap
if (lastReturnedIndex > 1 && compareToParent > 0) {
percolateUpMaxHeap(lastReturnedIndex);
} else {
percolateDownMaxHeap(lastReturnedIndex);
}
}
}
index--;
lastReturnedIndex = -1;
}
};
}
/**
* Returns a string representation of this heap. The returned string
* is similar to those produced by standard JDK collections.
*
* @return a string representation of this heap
*/
public String toString() {
final StringBuffer sb = new StringBuffer();
sb.append("[ ");
for (int i = 1; i < size + 1; i++) {
if (i != 1) {
sb.append(", ");
}
sb.append(elements[i]);
}
sb.append(" ]");
return sb.toString();
}
}