cern.colt.map

Class PrimeFinder

java.lang.Object

cern.colt.map.PrimeFinder

public class PrimeFinder
extends Object

Not of interest for users; only for implementors of hashtables. Used to keep hash table capacities prime numbers.

Choosing prime numbers as hash table capacities is a good idea to keep them working fast, particularly under hash table expansions.

However, JDK 1.2, JGL 3.1 and many other toolkits do nothing to keep capacities prime. This class provides efficient means to choose prime capacities.

Choosing a prime is O(log 300) (binary search in a list of 300 int's). Memory requirements: 1 KB static memory.

Version:

1.0, 09/24/99

Author:

wolfgang.hoschek@cern.ch

Field Summary

Fields

Modifier and Type	Field and Description
static int	largestPrime The largest prime this class can generate; currently equal to Integer.MAX_VALUE.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	PrimeFinder() Makes this class non instantiable, but still let's others inherit from it.

Method Summary

Methods

Modifier and Type	Method and Description
protected static void	main(String[] args) Tests correctness.
static int	nextPrime(int desiredCapacity) Returns a prime number which is >= desiredCapacity and very close to desiredCapacity (within 11% if desiredCapacity >= 1000).
protected static void	statistics(int from, int to) Tests correctness.

Methods inherited from class java.lang.Object

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

Field Detail

largestPrime

public static final int largestPrime

The largest prime this class can generate; currently equal to Integer.MAX_VALUE.

See Also:

Constant Field Values

Constructor Detail

PrimeFinder

protected PrimeFinder()

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

Method Detail

main

protected static void main(String[] args)

Tests correctness. Try from=1000, to=10000 from=200, to=1000 from=16, to=1000 from=1000, to=Integer.MAX_VALUE

nextPrime

public static 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.

statistics

protected static void statistics(int from,
              int to)

Tests correctness.