prefuse.util.collections
Class AbstractHashMap

java.lang.Object
  prefuse.util.collections.AbstractHashMap

Direct Known Subclasses:

IntObjectHashMap

public abstract class AbstractHashMap
extends java.lang.Object

Abstract base class for hash maps holding objects or primitive data types such as int, float, etc. as keys and/or values. First see the package summary and javadoc tree view to get the broad picture.

Note that implementations are not synchronized.

Version:

1.0, 09/24/99

Author:

wolfgang.hoschek@cern.ch

See Also:

HashMap

Field Summary

protected static int	defaultCapacity
protected static double	defaultMaxLoadFactor
protected static double	defaultMinLoadFactor
protected int	distinct The number of distinct associations in the map; its "size()".
protected int	highWaterMark
protected int	lowWaterMark The table capacity c=table.length always satisfies the invariant c * minLoadFactor <= s <= c * maxLoadFactor, where s=size() is the number of associations currently contained.
protected double	maxLoadFactor The maximum load factor for the hashtable.
protected double	minLoadFactor The minimum load factor for the hashtable.

Constructor Summary

protected

AbstractHashMap() Makes this class non instantiable, but still let's others inherit from it.

Method Summary

protected int	chooseGrowCapacity(int size, double minLoad, double maxLoad) Chooses a new prime table capacity optimized for growing that (approximately) satisfies the invariant c * minLoadFactor <= size <= c * maxLoadFactor and has at least one FREE slot for the given size.
protected int	chooseHighWaterMark(int capacity, double maxLoad) Returns new high water mark threshold based on current capacity and maxLoadFactor.
protected int	chooseLowWaterMark(int capacity, double minLoad) Returns new low water mark threshold based on current capacity and minLoadFactor.
protected int	chooseMeanCapacity(int size, double minLoad, double maxLoad) Chooses a new prime table capacity neither favoring shrinking nor growing, that (approximately) satisfies the invariant c * minLoadFactor <= size <= c * maxLoadFactor and has at least one FREE slot for the given size.
protected int	chooseShrinkCapacity(int size, double minLoad, double maxLoad) Chooses a new prime table capacity optimized for shrinking that (approximately) satisfies the invariant c * minLoadFactor <= size <= c * maxLoadFactor and has at least one FREE slot for the given size.
abstract void	clear() Removes all (key,value) associations from the receiver.
void	ensureCapacity(int minCapacity) Ensures that the receiver can hold at least the specified number of elements without needing to allocate new internal memory.
boolean	isEmpty() Returns true if the receiver contains no (key,value) associations.
protected int	nextPrime(int desiredCapacity) Returns a prime number which is >= desiredCapacity and very close to desiredCapacity (within 11% if desiredCapacity >= 1000).
protected void	setUp(int initialCapacity, double minLoadFactor, double maxLoadFactor) Initializes the receiver.
int	size() Returns the number of (key,value) associations currently contained.
void	trimToSize() Trims the capacity of the receiver to be the receiver's current size.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

distinct

protected int distinct

The number of distinct associations in the map; its "size()".

lowWaterMark

protected int lowWaterMark

The table capacity c=table.length always satisfies the invariant c * minLoadFactor <= s <= c * maxLoadFactor, where s=size() is the number of associations currently contained. The term "c * minLoadFactor" is called the "lowWaterMark", "c * maxLoadFactor" is called the "highWaterMark". In other words, the table capacity (and proportionally the memory used by this class) oscillates within these constraints. The terms are precomputed and cached to avoid recalculating them each time put(..) or removeKey(...) is called.

highWaterMark

protected int highWaterMark

minLoadFactor

protected double minLoadFactor

The minimum load factor for the hashtable.

maxLoadFactor

protected double maxLoadFactor

The maximum load factor for the hashtable.

defaultCapacity

protected static final int defaultCapacity

See Also:

Constant Field Values

defaultMinLoadFactor

protected static final double defaultMinLoadFactor

See Also:

Constant Field Values

defaultMaxLoadFactor

protected static final double defaultMaxLoadFactor

See Also:

Constant Field Values

Constructor Detail

AbstractHashMap

protected AbstractHashMap()

Makes this class non instantiable, but still let's others inherit from it.

Method Detail

chooseGrowCapacity

protected int chooseGrowCapacity(int size,
                                 double minLoad,
                                 double maxLoad)

Chooses a new prime table capacity optimized for growing that (approximately) satisfies the invariant c * minLoadFactor <= size <= c * maxLoadFactor and has at least one FREE slot for the given size.

chooseHighWaterMark

protected int chooseHighWaterMark(int capacity,
                                  double maxLoad)

Returns new high water mark threshold based on current capacity and maxLoadFactor.

Returns:

int the new threshold.

chooseLowWaterMark

protected int chooseLowWaterMark(int capacity,
                                 double minLoad)

Returns new low water mark threshold based on current capacity and minLoadFactor.

Returns:

int the new threshold.

chooseMeanCapacity

protected int chooseMeanCapacity(int size,
                                 double minLoad,
                                 double maxLoad)

Chooses a new prime table capacity neither favoring shrinking nor growing, that (approximately) satisfies the invariant c * minLoadFactor <= size <= c * maxLoadFactor and has at least one FREE slot for the given size.

chooseShrinkCapacity

protected int chooseShrinkCapacity(int size,
                                   double minLoad,
                                   double maxLoad)

Chooses a new prime table capacity optimized for shrinking that (approximately) satisfies the invariant c * minLoadFactor <= size <= c * maxLoadFactor and has at least one FREE slot for the given size.

clear

public abstract void clear()

Removes all (key,value) associations from the receiver.

ensureCapacity

public void ensureCapacity(int minCapacity)

Ensures that the receiver can hold at least the specified number of elements without needing to allocate new internal memory. If necessary, allocates new internal memory and increases the capacity of the receiver.

This method never need be called; it is for performance tuning only. Calling this method before put()ing a large number of associations boosts performance, because the receiver will grow only once instead of potentially many times.

This default implementation does nothing. Override this method if necessary.

Parameters:

minCapacity - the desired minimum capacity.

isEmpty

public boolean isEmpty()

Returns true if the receiver contains no (key,value) associations.

Returns:

true if the receiver contains no (key,value) associations.

nextPrime

protected int nextPrime(int desiredCapacity)

Returns a prime number which is >= desiredCapacity and very close to desiredCapacity (within 11% if desiredCapacity >= 1000).

Parameters:

desiredCapacity - the capacity desired by the user.

Returns:

the capacity which should be used for a hashtable.

setUp

protected void setUp(int initialCapacity,
                     double minLoadFactor,
                     double maxLoadFactor)

Initializes the receiver. You will almost certainly need to override this method in subclasses to initialize the hash table.

Parameters:

initialCapacity - the initial capacity of the receiver.

minLoadFactor - the minLoadFactor of the receiver.

maxLoadFactor - the maxLoadFactor of the receiver.

Throws:

java.lang.IllegalArgumentException - if initialCapacity < 0 || (minLoadFactor < 0.0 || minLoadFactor >= 1.0) || (maxLoadFactor <= 0.0 || maxLoadFactor >= 1.0) || (minLoadFactor >= maxLoadFactor).

size

public int size()

Returns the number of (key,value) associations currently contained.

Returns:

the number of (key,value) associations currently contained.

trimToSize

public void trimToSize()

Trims the capacity of the receiver to be the receiver's current size. Releases any superfluous internal memory. An application can use this operation to minimize the storage of the receiver.

This default implementation does nothing. Override this method if necessary.