org.apache.commons.math.util

Class ResizableDoubleArray

java.lang.Object

org.apache.commons.math.util.ResizableDoubleArray

All Implemented Interfaces:

java.io.Serializable, DoubleArray

public class ResizableDoubleArray
extends java.lang.Object
implements DoubleArray, java.io.Serializable

A variable length 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 initialCapacity property, which can be set by the constructor. The default initial capacity is 16. Adding elements using 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 expansionMode and expansionFactor properties. The expansionMode determines whether the size of the array is multiplied by the expansionFactor (MULTIPLICATIVE_MODE) or if the expansion is additive (ADDITIVE_MODE -- expansionFactor storage locations added). The default expansionMode is MULTIPLICATIVE_MODE and the default expansionFactor is 2.0.

The 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 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 numElements property) and if the difference is too large, the internal array is contracted to size numElements + 1. The determination of when the internal storage array is "too large" depends on the expansionMode and contractionFactor properties. If the expansionMode is MULTIPLICATIVE_MODE, contraction is triggered when the ratio between storage array length and numElements exceeds contractionFactor. If the expansionMode is ADDITIVE_MODE, the number of excess storage locations is compared to contractionFactor.

To avoid cycles of expansions and contractions, the expansionFactor must not exceed the contractionFactor. Constructors and mutators for both of these properties enforce this requirement, throwing IllegalArgumentException if it is violated.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static int	ADDITIVE_MODE additive expansion mode
static int	MULTIPLICATIVE_MODE multiplicative expansion mode

Constructor Summary

Constructors

Constructor and Description
ResizableDoubleArray() Create a ResizableArray with default properties.
ResizableDoubleArray(double[] initialArray) Create a ResizableArray from an existing double[] with the initial capacity and numElements corresponding to the size of the supplied double[] array.
ResizableDoubleArray(int initialCapacity) Create a ResizableArray with the specified initial capacity.
ResizableDoubleArray(int initialCapacity, float expansionFactor) Create a ResizableArray with the specified initial capacity and expansion factor.
ResizableDoubleArray(int initialCapacity, float expansionFactor, float contractionCriteria) Create a ResizableArray with the specified initialCapacity, expansionFactor, and contractionCriteria.
ResizableDoubleArray(int initialCapacity, float expansionFactor, float contractionCriteria, int expansionMode) Create a ResizableArray with the specified properties.
ResizableDoubleArray(ResizableDoubleArray original) Copy constructor.

Method Summary

Modifier and Type	Method and Description
void	addElement(double value) Adds an element to the end of this expandable array.
double	addElementRolling(double value) Adds an element to the end of the array and removes the first element in the array.
void	addElements(double[] values) Adds several element to the end of this expandable array.
void	clear() Clear the array, reset the size to the initialCapacity and the number of elements to zero.
void	contract() Contracts the storage array to the (size of the element set) + 1 - to avoid a zero length array.
ResizableDoubleArray	copy() Returns a copy of the ResizableDoubleArray.
static void	copy(ResizableDoubleArray source, ResizableDoubleArray dest) Copies source to dest, copying the underlying data, so dest is a new, independent copy of source.
void	discardFrontElements(int i) Discards the i initial elements of the array.
void	discardMostRecentElements(int i) Discards the i last elements of the array.
boolean	equals(java.lang.Object object) Returns true iff object is a ResizableDoubleArray with the same properties as this and an identical internal storage array.
float	getContractionCriteria() The contraction criteria defines when the internal array will contract to store only the number of elements in the element array.
double	getElement(int index) Returns the element at the specified index
double[]	getElements() Returns a double array containing the elements of this ResizableArray.
float	getExpansionFactor() The expansion factor controls the size of a new array when an array needs to be expanded.
int	getExpansionMode() The expansionMode determines whether the internal storage array grows additively (ADDITIVE_MODE) or multiplicatively (MULTIPLICATIVE_MODE) when it is expanded.
double[]	getInternalValues() Returns the internal storage array.
int	getNumElements() Returns the number of elements currently in the array.
double[]	getValues() Deprecated. replaced by getInternalValues() as of 2.0
int	hashCode() Returns a hash code consistent with equals.
void	setContractionCriteria(float contractionCriteria) Sets the contraction criteria for this ExpandContractDoubleArray.
void	setElement(int index, double value) Sets the element at the specified index.
void	setExpansionFactor(float expansionFactor) Sets the expansionFactor.
void	setExpansionMode(int expansionMode) Sets the expansionMode.
void	setNumElements(int i) 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.
int	start() Returns the starting index of the internal array.
double	substituteMostRecentElement(double value) Substitutes value for the most recently added value.

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

ADDITIVE_MODE

public static final int ADDITIVE_MODE

additive expansion mode

See Also:

Constant Field Values

MULTIPLICATIVE_MODE

public static final int MULTIPLICATIVE_MODE

multiplicative expansion mode

See Also:

Constant Field Values

Constructor Detail

ResizableDoubleArray

public ResizableDoubleArray()

Create a ResizableArray with default properties.

• initialCapacity = 16
• expansionMode = MULTIPLICATIVE_MODE
• expansionFactor = 2.5
• contractionFactor = 2.0

ResizableDoubleArray

public ResizableDoubleArray(int initialCapacity)

Create a ResizableArray with the specified initial capacity. Other properties take default values:

• expansionMode = MULTIPLICATIVE_MODE
• expansionFactor = 2.5
• contractionFactor = 2.0

Parameters:

initialCapacity - The initial size of the internal storage array

Throws:

java.lang.IllegalArgumentException - if initialCapacity is not > 0

ResizableDoubleArray

public ResizableDoubleArray(double[] initialArray)

Create a ResizableArray from an existing double[] with the initial capacity and numElements corresponding to the size of the supplied double[] array. If the supplied array is null, a new empty array with the default initial capacity will be created. The input array is copied, not referenced. Other properties take default values:

• initialCapacity = 16
• expansionMode = MULTIPLICATIVE_MODE
• expansionFactor = 2.5
• contractionFactor = 2.0

Parameters:

initialArray - initial array

Since:

2.2

ResizableDoubleArray

public ResizableDoubleArray(int initialCapacity,
                            float expansionFactor)

Create a ResizableArray with the specified initial capacity and expansion factor. The remaining properties take default values:

• expansionMode = MULTIPLICATIVE_MODE
• contractionFactor = 0.5 + expansionFactor

Throws IllegalArgumentException if the following conditions are not met:

• initialCapacity > 0
• expansionFactor > 1

Parameters:

initialCapacity - The initial size of the internal storage array

expansionFactor - the array will be expanded based on this parameter

Throws:

java.lang.IllegalArgumentException - if parameters are not valid

ResizableDoubleArray

public ResizableDoubleArray(int initialCapacity,
                            float expansionFactor,
                            float contractionCriteria)

Create a ResizableArray with the specified initialCapacity, expansionFactor, and contractionCriteria. The expansionMode will default to MULTIPLICATIVE_MODE.

Throws IllegalArgumentException if the following conditions are not met:

• initialCapacity > 0
• expansionFactor > 1
• contractionFactor >= expansionFactor

Parameters:

initialCapacity - The initial size of the internal storage array

expansionFactor - the array will be expanded based on this parameter

contractionCriteria - The contraction Criteria.

Throws:

java.lang.IllegalArgumentException - if parameters are not valid

ResizableDoubleArray

public ResizableDoubleArray(int initialCapacity,
                            float expansionFactor,
                            float contractionCriteria,
                            int expansionMode)

Create a ResizableArray with the specified properties.

Throws IllegalArgumentException if the following conditions are not met:

• initialCapacity > 0
• expansionFactor > 1
• contractionFactor >= expansionFactor
• expansionMode in {MULTIPLICATIVE_MODE, ADDITIVE_MODE}

Parameters:

initialCapacity - the initial size of the internal storage array

expansionFactor - the array will be expanded based on this parameter

contractionCriteria - the contraction Criteria

expansionMode - the expansion mode

Throws:

java.lang.IllegalArgumentException - if parameters are not valid

ResizableDoubleArray

public ResizableDoubleArray(ResizableDoubleArray original)

Copy constructor. Creates a new ResizableDoubleArray that is a deep, fresh copy of the original. Needs to acquire synchronization lock on original. Original may not be null; otherwise a NullPointerException is thrown.

Parameters:

original - array to copy

Since:

2.0

Method Detail

addElement

public void addElement(double value)

Adds an element to the end of this expandable array.

Specified by:

addElement in interface DoubleArray

Parameters:

value - to be added to end of array

addElements

public void addElements(double[] values)

Adds several element to the end of this expandable array.

Parameters:

values - to be added to end of array

Since:

2.2

addElementRolling

public double addElementRolling(double value)

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.

Specified by:

addElementRolling in interface DoubleArray

Parameters:

value - the value to be added to the array

Returns:

the value which has been discarded or "pushed" out of the array by this rolling insert

substituteMostRecentElement

public double substituteMostRecentElement(double value)

Substitutes value for the most recently added value. Returns the value that has been replaced. If the array is empty (i.e. if numElements is zero), a MathRuntimeException is thrown.

Parameters:

value - new value to substitute for the most recently added value

Returns:

value that has been replaced in the array

Since:

2.0

clear

public void clear()

Clear the array, reset the size to the initialCapacity and the number of elements to zero.

Specified by:

clear in interface DoubleArray

contract

public void contract()

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.

discardFrontElements

public void discardFrontElements(int i)

Discards the i initial elements of the array. For example, if the array contains the elements 1,2,3,4, invoking discardFrontElements(2) will cause the first two elements to be discarded, leaving 3,4 in the array. Throws illegalArgumentException if i exceeds numElements.

Parameters:

i - the number of elements to discard from the front of the array

Throws:

java.lang.IllegalArgumentException - if i is greater than numElements.

Since:

2.0

discardMostRecentElements

public void discardMostRecentElements(int i)

Discards the i last elements of the array. For example, if the array contains the elements 1,2,3,4, invoking discardMostRecentElements(2) will cause the last two elements to be discarded, leaving 1,2 in the array. Throws illegalArgumentException if i exceeds numElements.

Parameters:

i - the number of elements to discard from the end of the array

Throws:

java.lang.IllegalArgumentException - if i is greater than numElements.

Since:

2.0

getContractionCriteria

public float getContractionCriteria()

The contraction criteria defines when the internal array will contract to store only the number of elements in the element array. If the expansionMode is MULTIPLICATIVE_MODE, contraction is triggered when the ratio between storage array length and numElements exceeds contractionFactor. If the expansionMode is ADDITIVE_MODE, the number of excess storage locations is compared to contractionFactor.

Returns:

the contraction criteria used to reclaim memory.

getElement

public double getElement(int index)

Returns the element at the specified index

Specified by:

getElement in interface DoubleArray

Parameters:

index - index to fetch a value from

Returns:

value stored at the specified index

Throws:

java.lang.ArrayIndexOutOfBoundsException - if index is less than zero or is greater than getNumElements() - 1.

getElements

public double[] getElements()

Returns a double array containing the elements of this ResizableArray. 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 ResizableArray.

Specified by:

getElements in interface DoubleArray

Returns:

the double array.

getExpansionFactor

public float getExpansionFactor()

The expansion factor controls the size of a new array when an array needs to be expanded. The expansionMode determines whether the size of the array is multiplied by the expansionFactor (MULTIPLICATIVE_MODE) or if the expansion is additive (ADDITIVE_MODE -- expansionFactor storage locations added). The default expansionMode is MULTIPLICATIVE_MODE and the default expansionFactor is 2.0.

Returns:

the expansion factor of this expandable double array

getExpansionMode

public int getExpansionMode()

The expansionMode determines whether the internal storage array grows additively (ADDITIVE_MODE) or multiplicatively (MULTIPLICATIVE_MODE) when it is expanded.

Returns:

Returns the expansionMode.

getNumElements

public int getNumElements()

Returns the number of elements currently in the array. Please note that this is different from the length of the internal storage array.

Specified by:

getNumElements in interface DoubleArray

Returns:

number of elements

getValues

@Deprecated
public double[] getValues()

Deprecated. replaced by getInternalValues() as of 2.0

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 startIndex is required (available via the start() method). This method should only be used in cases where copying the internal array is not practical. The getElements() method should be used in all other cases.

Returns:

the internal storage array used by this object

getInternalValues

public double[] getInternalValues()

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 startIndex is required (available via the start() method). This method should only be used in cases where copying the internal array is not practical. The getElements() method should be used in all other cases.

Returns:

the internal storage array used by this object

Since:

2.0

setContractionCriteria

public void setContractionCriteria(float contractionCriteria)

Sets the contraction criteria for this ExpandContractDoubleArray.

Parameters:

contractionCriteria - contraction criteria

setElement

public void setElement(int index,
                       double value)

Sets the element at the specified index. If the specified index is greater than getNumElements() - 1, the numElements property is increased to index +1 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).

Specified by:

setElement in interface DoubleArray

Parameters:

index - index to store a value in

value - value to store at the specified index

Throws:

java.lang.ArrayIndexOutOfBoundsException - if index is less than zero.

setExpansionFactor

public void setExpansionFactor(float expansionFactor)

Sets the expansionFactor. Throws IllegalArgumentException if the the following conditions are not met:

• expansionFactor > 1
• contractionFactor >= expansionFactor

Parameters:

expansionFactor - the new expansion factor value.

Throws:

java.lang.IllegalArgumentException - if expansionFactor is <= 1 or greater than contractionFactor

setExpansionMode

public void setExpansionMode(int expansionMode)

Sets the expansionMode. The specified value must be one of ADDITIVE_MODE, MULTIPLICATIVE_MODE.

Parameters:

expansionMode - The expansionMode to set.

Throws:

java.lang.IllegalArgumentException - if the specified mode value is not valid

setNumElements

public void setNumElements(int i)

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.

Parameters:

i - a new number of elements

Throws:

java.lang.IllegalArgumentException - if i is negative.

start

public int start()

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 internalArray[startIndex],...,internalArray[startIndex + numElements -1]

Returns:

starting index

copy

public static void copy(ResizableDoubleArray source,
                        ResizableDoubleArray dest)

Copies source to dest, copying the underlying data, so dest is a new, independent copy of source. Does not contract before the copy.

Obtains synchronization locks on both source and dest (in that order) before performing the copy.

Neither source nor dest may be null; otherwise a NullPointerException is thrown

Parameters:

source - ResizableDoubleArray to copy

dest - ResizableArray to replace with a copy of the source array

Since:

2.0

copy

public ResizableDoubleArray copy()

Returns a copy of the ResizableDoubleArray. Does not contract before the copy, so the returned object is an exact copy of this.

Returns:

a new ResizableDoubleArray with the same data and configuration properties as this

Since:

2.0

equals

public boolean equals(java.lang.Object object)

Returns true iff object is a ResizableDoubleArray with the same properties as this and an identical internal storage array.

Overrides:

equals in class java.lang.Object

Parameters:

object - object to be compared for equality with this

Returns:

true iff object is a ResizableDoubleArray with the same data and properties as this

Since:

2.0

hashCode

public int hashCode()

Returns a hash code consistent with equals.

Overrides:

hashCode in class java.lang.Object

Returns:

hash code representing this ResizableDoubleArray

Since:

2.0