Mega Code Archive
A variable length Double Array
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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.
*/
import java.io.Serializable;
/**
*
* A variable length {@link DoubleArray} implementation that automatically
* handles expanding and contracting its internal storage array as elements are
* added and removed.
*
* The internal storage array starts with capacity determined by the
* <code>initialCapacity</code> property, which can be set by the constructor.
* The default initial capacity is 16. Adding elements using
* {@link #addElement(double)} appends elements to the end of the array. When
* there are no open entries at the end of the internal storage array, the array
* is expanded. The size of the expanded array depends on the
* <code>expansionMode</code> and <code>expansionFactor</code> properties.
* The <code>expansionMode</code> determines whether the size of the array is
* multiplied by the <code>expansionFactor</code> (MULTIPLICATIVE_MODE) or if
* the expansion is additive (ADDITIVE_MODE -- <code>expansionFactor</code>
* storage locations added). The default <code>expansionMode</code> is
* MULTIPLICATIVE_MODE and the default <code>expansionFactor</code> is 2.0.
*
* The {@link #addElementRolling(double)} method adds a new element to the end
* of the internal storage array and adjusts the "usable window" of the internal
* array forward by one position (effectively making what was the second element
* the first, and so on). Repeated activations of this method (or activation of
* {@link #discardFrontElements(int)}) will effectively orphan the storage
* locations at the beginning of the internal storage array. To reclaim this
* storage, each time one of these methods is activated, the size of the
* internal storage array is compared to the number of addressable elements (the
* <code>numElements</code> property) and if the difference is too large, the
* internal array is contracted to size <code>numElements + 1.</code> The
* determination of when the internal storage array is "too large" depends on
* the <code>expansionMode</code> and <code>contractionFactor</code>
* properties. If the <code>expansionMode</code> is
* <code>MULTIPLICATIVE_MODE</code>, contraction is triggered when the ratio
* between storage array length and <code>numElements</code> exceeds
* <code>contractionFactor.</code> If the <code>expansionMode</code> is
* <code>ADDITIVE_MODE,</code> the number of excess storage locations is
* compared to <code>contractionFactor.</code>
*
* To avoid cycles of expansions and contractions, the
* <code>expansionFactor</code> must not exceed the
* <code>contractionFactor.</code> Constructors and mutators for both of these
* properties enforce this requirement, throwing IllegalArgumentException if it
* is violated.
*
* @version $Revision: 618057 $ $Date: 2008-02-03 11:58:54 -0700 (Sun, 03 Feb
* 2008) $
*/
public class ResizableDoubleArray implements Serializable {
/** Serializable version identifier */
private static final long serialVersionUID = -3485529955529426875L;
/** additive expansion mode */
public static final int ADDITIVE_MODE = 1;
/** multiplicative expansion mode */
public static final int MULTIPLICATIVE_MODE = 0;
/**
* The contraction criteria determines when the internal array will be
* contracted to fit the number of elements contained in the element array +
* 1.
*/
protected float contractionCriteria = 2.5f;
/**
* The expansion factor of the array. When the array needs to be expanded, the
* new array size will be <code>internalArray.length * expansionFactor</code>
* if <code>expansionMode</code> is set to MULTIPLICATIVE_MODE, or
* <code>internalArray.length + expansionFactor</code> if
* <code>expansionMode</code> is set to ADDITIVE_MODE.
*/
protected float expansionFactor = 2.0f;
/**
* Determines whether array expansion by <code>expansionFactor</code> is
* additive or multiplicative.
*/
protected int expansionMode = MULTIPLICATIVE_MODE;
/**
* The initial capacity of the array. Initial capacity is not exposed as a
* property as it is only meaningful when passed to a constructor.
*/
protected int initialCapacity = 16;
/**
* The internal storage array.
*/
protected double[] internalArray;
/**
* The number of addressable elements in the array. Note that this has nothing
* to do with the length of the internal storage array.
*/
protected int numElements = 0;
/**
* The position of the first addressable element in the internal storage
* array. The addressable elements in the array are <code>
* internalArray[startIndex],...,internalArray[startIndex + numElements -1]
* </code>
*/
protected int startIndex = 0;
/**
* Create a ResizableArray with default properties.
* <ul>
* <li><code>initialCapacity = 16</code></li>
* <li><code>expansionMode = MULTIPLICATIVE_MODE</code></li>
* <li><code>expansionFactor = 2.5</code></li>
* <li><code>contractionFactor = 2.0</code></li>
* </ul>
*/
public ResizableDoubleArray() {
internalArray = new double[initialCapacity];
}
/**
* Create a ResizableArray with the specified initial capacity. Other
* properties take default values:
* <ul>
* <li><code>expansionMode = MULTIPLICATIVE_MODE</code></li>
* <li><code>expansionFactor = 2.5</code></li>
* <li><code>contractionFactor = 2.0</code></li>
* </ul>
*
* @param initialCapacity
* The initial size of the internal storage array
* @throws IllegalArgumentException
* if initialCapacity is not > 0
*/
public ResizableDoubleArray(int initialCapacity) {
setInitialCapacity(initialCapacity);
internalArray = new double[this.initialCapacity];
}
/**
*
* Create a ResizableArray with the specified initial capacity and expansion
* factor. The remaining properties take default values:
* <ul>
* <li><code>expansionMode = MULTIPLICATIVE_MODE</code></li>
* <li><code>contractionFactor = 0.5 + expansionFactor</code></li>
* </ul>
*
* Throws IllegalArgumentException if the following conditions are not met:
* <ul>
* <li><code>initialCapacity > 0</code></li>
* <li><code>expansionFactor > 1</code></li>
* </ul>
*
* @param initialCapacity
* The initial size of the internal storage array
* @param expansionFactor
* the array will be expanded based on this parameter
* @throws IllegalArgumentException
* if parameters are not valid
*/
public ResizableDoubleArray(int initialCapacity, float expansionFactor) {
this.expansionFactor = expansionFactor;
setInitialCapacity(initialCapacity);
internalArray = new double[initialCapacity];
setContractionCriteria(expansionFactor + 0.5f);
}
/**
*
* Create a ResizableArray with the specified initialCapacity,
* expansionFactor, and contractionCriteria. The <code>expansionMode</code>
* will default to <code>MULTIPLICATIVE_MODE.</code>
*
* Throws IllegalArgumentException if the following conditions are not met:
* <ul>
* <li><code>initialCapacity > 0</code></li>
* <li><code>expansionFactor > 1</code></li>
* <li><code>contractionFactor >= expansionFactor</code></li>
* </ul>
*
* @param initialCapacity
* The initial size of the internal storage array
* @param expansionFactor
* the array will be expanded based on this parameter
* @param contractionCriteria
* The contraction Criteria.
* @throws IllegalArgumentException
* if parameters are not valid
*/
public ResizableDoubleArray(int initialCapacity, float expansionFactor, float contractionCriteria) {
this.expansionFactor = expansionFactor;
setContractionCriteria(contractionCriteria);
setInitialCapacity(initialCapacity);
internalArray = new double[initialCapacity];
}
/**
*
* Create a ResizableArray with the specified properties.
*
* Throws IllegalArgumentException if the following conditions are not met:
* <ul>
* <li><code>initialCapacity > 0</code></li>
* <li><code>expansionFactor > 1</code></li>
* <li><code>contractionFactor >= expansionFactor</code></li>
* <li><code>expansionMode in {MULTIPLICATIVE_MODE, ADDITIVE_MODE}</code>
* </li>
* </ul>
*
* @param initialCapacity
* the initial size of the internal storage array
* @param expansionFactor
* the array will be expanded based on this parameter
* @param contractionCriteria
* the contraction Criteria
* @param expansionMode
* the expansion mode
* @throws IllegalArgumentException
* if parameters are not valid
*/
public ResizableDoubleArray(int initialCapacity, float expansionFactor,
float contractionCriteria, int expansionMode) {
this.expansionFactor = expansionFactor;
setContractionCriteria(contractionCriteria);
setInitialCapacity(initialCapacity);
setExpansionMode(expansionMode);
internalArray = new double[initialCapacity];
}
/**
* Adds an element to the end of this expandable array.
*
* @param value
* to be added to end of array
*/
public synchronized void addElement(double value) {
numElements++;
if ((startIndex + numElements) > internalArray.length) {
expand();
}
internalArray[startIndex + (numElements - 1)] = value;
if (shouldContract()) {
contract();
}
}
/**
*
* Adds an element to the end of the array and removes the first element in
* the array. Returns the discarded first element. The effect is similar to a
* push operation in a FIFO queue.
*
* Example: If the array contains the elements 1, 2, 3, 4 (in that order) and
* addElementRolling(5) is invoked, the result is an array containing the
* entries 2, 3, 4, 5 and the value returned is 1.
*
* @param value
* the value to be added to the array
* @return the value which has been discarded or "pushed" out of the array by
* this rolling insert
*/
public synchronized double addElementRolling(double value) {
double discarded = internalArray[startIndex];
if ((startIndex + (numElements + 1)) > internalArray.length) {
expand();
}
// Increment the start index
startIndex += 1;
// Add the new value
internalArray[startIndex + (numElements - 1)] = value;
// Check the contraction criteria
if (shouldContract()) {
contract();
}
return discarded;
}
/**
* Checks the expansion factor and the contraction criteria and throws an
* IllegalArgumentException if the contractionCriteria is less than the
* expansionCriteria
*
* @param expansionFactor
* factor to be checked
* @param contractionCritera
* critera to be checked
* @throws IllegalArgumentException
* if the contractionCriteria is less than the expansionCriteria.
*/
protected void checkContractExpand(float contractionCritera, float expansionFactor) {
if (contractionCritera < expansionFactor) {
String msg = "Contraction criteria can never be smaller than "
+ "the expansion factor. This would lead to a never "
+ "ending loop of expansion and contraction as a newly "
+ "expanded internal storage array would immediately "
+ "satisfy the criteria for contraction";
throw new IllegalArgumentException(msg);
}
if (contractionCriteria <= 1.0) {
String msg = "The contraction criteria must be a number larger "
+ "than one. If the contractionCriteria is less than or "
+ "equal to one an endless loop of contraction and "
+ "expansion would ensue as an internalArray.length "
+ "== numElements would satisfy the contraction criteria";
throw new IllegalArgumentException(msg);
}
if (expansionFactor <= 1.0) {
String msg = "The expansion factor must be a number greater than 1.0";
throw new IllegalArgumentException(msg);
}
}
/**
* Clear the array, reset the size to the initialCapacity and the number of
* elements to zero.
*/
public synchronized void clear() {
numElements = 0;
internalArray = new double[initialCapacity];
}
/**
* Contracts the storage array to the (size of the element set) + 1 - to avoid
* a zero length array. This function also resets the startIndex to zero.
*/
public synchronized void contract() {
double[] tempArray = new double[numElements + 1];
// Copy and swap - copy only the element array from the src array.
System.arraycopy(internalArray, startIndex, tempArray, 0, numElements);
internalArray = tempArray;
// Reset the start index to zero
startIndex = 0;
}
/**
* Discards the <code>i<code> initial elements of the array. For example,
* if the array contains the elements 1,2,3,4, invoking
* <code>discardFrontElements(2)</code> will cause the first two elements
* to be discarded, leaving 3,4 in the array. Throws illegalArgumentException
* if i exceeds numElements.
*
* @param i the number of elements to discard from the front of the array
* @throws IllegalArgumentException if i is greater than numElements.
*/
public synchronized void discardFrontElements(int i) {
if (i > numElements) {
String msg = "Cannot discard more elements than are" + "contained in this array.";
throw new IllegalArgumentException(msg);
} else if (i < 0) {
String msg = "Cannot discard a negative number of elements.";
throw new IllegalArgumentException(msg);
} else {
// "Subtract" this number of discarded from numElements
numElements -= i;
startIndex += i;
}
if (shouldContract()) {
contract();
}
}
/**
* Expands the internal storage array using the expansion factor.
*
* if <code>expansionMode</code> is set to MULTIPLICATIVE_MODE, the new
* array size will be <code>internalArray.length * expansionFactor.</code>
* If <code>expansionMode</code> is set to ADDITIVE_MODE, the length after
* expansion will be <code>internalArray.length + expansionFactor</code>
*
*/
protected synchronized void expand() {
// notice the use of Math.ceil(), this gaurantees that we will always
// have an array of at least currentSize + 1. Assume that the
// current initial capacity is 1 and the expansion factor
// is 1.000000000000000001. The newly calculated size will be
// rounded up to 2 after the multiplication is performed.
int newSize = 0;
if (expansionMode == MULTIPLICATIVE_MODE) {
newSize = (int) Math.ceil(internalArray.length * expansionFactor);
} else {
newSize = internalArray.length + Math.round(expansionFactor);
}
double[] tempArray = new double[newSize];
// Copy and swap
System.arraycopy(internalArray, 0, tempArray, 0, internalArray.length);
internalArray = tempArray;
}
/**
* Expands the internal storage array to the specified size.
*
* @param size
* Size of the new internal storage array
*/
private synchronized void expandTo(int size) {
double[] tempArray = new double[size];
// Copy and swap
System.arraycopy(internalArray, 0, tempArray, 0, internalArray.length);
internalArray = tempArray;
}
/**
* The contraction criteria defines when the internal array will contract to
* store only the number of elements in the element array. If the
* <code>expansionMode</code> is <code>MULTIPLICATIVE_MODE</code>,
* contraction is triggered when the ratio between storage array length and
* <code>numElements</code> exceeds <code>contractionFactor</code>. If
* the <code>expansionMode</code> is <code>ADDITIVE_MODE</code>, the
* number of excess storage locations is compared to
* <code>contractionFactor.</code>
*
* @return the contraction criteria used to reclaim memory.
*/
public float getContractionCriteria() {
return contractionCriteria;
}
/**
* Returns the element at the specified index
*
* @param index
* index to fetch a value from
* @return value stored at the specified index
* @throws ArrayIndexOutOfBoundsException
* if <code>index</code> is less than zero or is greater than
* <code>getNumElements() - 1</code>.
*/
public synchronized double getElement(int index) {
if (index >= numElements) {
String msg = "The index specified: " + index
+ " is larger than the current number of elements";
throw new ArrayIndexOutOfBoundsException(msg);
} else if (index >= 0) {
return internalArray[startIndex + index];
} else {
String msg = "Elements cannot be retrieved from a negative array index";
throw new ArrayIndexOutOfBoundsException(msg);
}
}
/**
* Returns a double array containing the elements of this
* <code>ResizableArray</code>. This method returns a copy, not a reference
* to the underlying array, so that changes made to the returned array have no
* effect on this <code>ResizableArray.</code>
*
* @return the double array.
*/
public synchronized double[] getElements() {
double[] elementArray = new double[numElements];
System.arraycopy(internalArray, startIndex, elementArray, 0, numElements);
return elementArray;
}
/**
* The expansion factor controls the size of a new aray when an array needs to
* be expanded. The <code>expansionMode</code> determines whether the size
* of the array is multiplied by the <code>expansionFactor</code>
* (MULTIPLICATIVE_MODE) or if the expansion is additive (ADDITIVE_MODE --
* <code>expansionFactor</code> storage locations added). The default
* <code>expansionMode</code> is MULTIPLICATIVE_MODE and the default
* <code>expansionFactor</code> is 2.0.
*
* @return the expansion factor of this expandable double array
*/
public float getExpansionFactor() {
return expansionFactor;
}
/**
* The <code>expansionMode</code> determines whether the internal storage
* array grows additively (ADDITIVE_MODE) or multiplicatively
* (MULTIPLICATIVE_MODE) when it is expanded.
*
* @return Returns the expansionMode.
*/
public int getExpansionMode() {
return expansionMode;
}
/**
* Notice the package scope on this method. This method is simply here for the
* JUnit test, it allows us check if the expansion is working properly after a
* number of expansions. This is not meant to be a part of the public
* interface of this class.
*
* @return the length of the internal storage array.
*/
synchronized int getInternalLength() {
return (internalArray.length);
}
/**
* Returns the number of elements currently in the array. Please note that
* this is different from the length of the internal storage array.
*
* @return number of elements
*/
public synchronized int getNumElements() {
return (numElements);
}
/**
* Returns the internal storage array. Note that this method returns a
* reference to the internal storage array, not a copy, and to correctly
* address elements of the array, the <code>startIndex</code> is required
* (available via the {@link #start} method). This method should only be used
* in cases where copying the internal array is not practical. The
* {@link #getElements} method should be used in all other cases.
*
* @return the internal storage array used by this object
*/
public synchronized double[] getValues() {
return (internalArray);
}
/**
* Sets the contraction criteria for this ExpandContractDoubleArray.
*
* @param contractionCriteria
* contraction criteria
*/
public void setContractionCriteria(float contractionCriteria) {
checkContractExpand(contractionCriteria, getExpansionFactor());
this.contractionCriteria = contractionCriteria;
}
/**
* Sets the element at the specified index. If the specified index is greater
* than <code>getNumElements() - 1</code>, the <code>numElements</code>
* property is increased to <code>index +1</code> and additional storage is
* allocated (if necessary) for the new element and all (uninitialized)
* elements between the new element and the previous end of the array).
*
* @param index
* index to store a value in
* @param value
* value to store at the specified index
* @throws ArrayIndexOutOfBoundsException
* if <code>index</code> is less than zero.
*/
public synchronized void setElement(int index, double value) {
if (index < 0) {
String msg = "Cannot set an element at a negative index";
throw new ArrayIndexOutOfBoundsException(msg);
}
if (index + 1 > numElements) {
numElements = index + 1;
}
if ((startIndex + index) >= internalArray.length) {
expandTo(startIndex + (index + 1));
}
internalArray[startIndex + index] = value;
}
/**
* Sets the expansionFactor. Throws IllegalArgumentException if the the
* following conditions are not met:
* <ul>
* <li><code>expansionFactor > 1</code></li>
* <li><code>contractionFactor >= expansionFactor</code></li>
* </ul>
*
* @param expansionFactor
* the new expansion factor value.
* @throws IllegalArgumentException
* if expansionFactor is <= 1 or greater than contractionFactor
*/
public void setExpansionFactor(float expansionFactor) {
checkContractExpand(getContractionCriteria(), expansionFactor);
// The check above verifies that the expansion factor is > 1.0;
this.expansionFactor = expansionFactor;
}
/**
* Sets the <code>expansionMode</code>. The specified value must be one of
* ADDITIVE_MODE, MULTIPLICATIVE_MODE.
*
* @param expansionMode
* The expansionMode to set.
* @throws IllegalArgumentException
* if the specified mode value is not valid
*/
public void setExpansionMode(int expansionMode) {
if (expansionMode != MULTIPLICATIVE_MODE && expansionMode != ADDITIVE_MODE) {
throw new IllegalArgumentException("Illegal expansionMode setting.");
}
this.expansionMode = expansionMode;
}
/**
* Sets the initial capacity. Should only be invoked by constructors.
*
* @param initialCapacity
* of the array
* @throws IllegalArgumentException
* if <code>initialCapacity</code> is not positive.
*/
protected void setInitialCapacity(int initialCapacity) {
if (initialCapacity > 0) {
synchronized (this) {
this.initialCapacity = initialCapacity;
}
} else {
String msg = "The initial capacity supplied: " + initialCapacity
+ "must be a positive integer";
throw new IllegalArgumentException(msg);
}
}
/**
* This function allows you to control the number of elements contained in
* this array, and can be used to "throw out" the last n values in an array.
* This function will also expand the internal array as needed.
*
* @param i
* a new number of elements
* @throws IllegalArgumentException
* if <code>i</code> is negative.
*/
public synchronized void setNumElements(int i) {
// If index is negative thrown an error
if (i < 0) {
String msg = "Number of elements must be zero or a positive " + "integer";
throw new IllegalArgumentException(msg);
}
// Test the new num elements, check to see if the array needs to be
// expanded to accomodate this new number of elements
if ((startIndex + i) > internalArray.length) {
expandTo(startIndex + i);
}
// Set the new number of elements to new value
numElements = i;
}
/**
* Returns true if the internal storage array has too many unused storage
* positions.
*
* @return true if array satisfies the contraction criteria
*/
private synchronized boolean shouldContract() {
if (expansionMode == MULTIPLICATIVE_MODE) {
return (internalArray.length / ((float) numElements)) > contractionCriteria;
} else {
return (internalArray.length - numElements) > contractionCriteria;
}
}
/**
* Returns the starting index of the internal array. The starting index is the
* position of the first addressable element in the internal storage array.
* The addressable elements in the array are <code>
* internalArray[startIndex],...,internalArray[startIndex + numElements -1]
* </code>
*
* @return starting index
*/
public synchronized int start() {
return startIndex;
}
}
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