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java.lang.Objectcern.colt.map.PrimeFinder
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 | |
static int |
largestPrime
The largest prime this class can generate; currently equal to Integer.MAX_VALUE. |
Constructor Summary | |
protected |
PrimeFinder()
Makes this class non instantiable, but still let's others inherit from it. |
Method Summary | |
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 |
public static final int largestPrime
Constructor Detail |
protected PrimeFinder()
Method Detail |
protected static void main(String[] args)
public static int nextPrime(int desiredCapacity)
>= desiredCapacity
and very close to desiredCapacity
(within 11% if desiredCapacity >= 1000
).
desiredCapacity
- the capacity desired by the user.
protected static void statistics(int from, int to)
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