cern.colt.map

Class PrimeFinder

java.lang.Object

cern.colt.map.PrimeFinder

public class PrimeFinder
extends java.lang.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.

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.

Method Summary

Modifier and Type	Method and Description
static int	nextPrime(int desiredCapacity) Returns a prime number which is >= desiredCapacity and very close to desiredCapacity (within 11% if desiredCapacity >= 1000).

Methods inherited from class java.lang.Object

equals, 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

Method Detail

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.