org.biojava.nbio.core.util

Class Hashcoder

java.lang.Object

org.biojava.nbio.core.util.Hashcoder

public class Hashcoder
extends Object

Contains helper methods for generating a HashCode without having to resort to the commons lang hashcode builders. Example where the property name is a String and the property age is an int

 public int hashCode() {
   int result = Hashcoder.SEED;
   result = Hashcoder.hash(result, this.getName());
   result = Hashcoder.hash(result, this.getAge());
   return result;
 }
 

Author:

ayates

Field Summary

Fields

Modifier and Type	Field and Description
static int	PRIME The prime number used to multiply any calculated hashcode seed by i.e. result = PRIME*result + c Where result is the result of the previous calculation (at first this will be seed) and c is the calculated int to add to result
static int	SEED An initial value for a hashCode, to which we add contributions from fields.

Constructor Summary

Constructors

Constructor and Description
Hashcoder()

Method Summary

Modifier and Type	Method and Description
static int	hash(int seed, boolean b)
static int	hash(int seed, char c)
static int	hash(int seed, double d) double support which is done using the same techinque as float hashing except we convert to a long not to an int.
static int	hash(int seed, float f) float support done via Float.floatToIntBits(float) which allows the encoding of a float as an int.
static int	hash(int seed, int i) Used for ints, bytes and shorts
static int	hash(int seed, long l) long support done by shifting by 32 (using unsigned shift)
static int	hash(int seed, Object o) o is a possibly-null object field, and possibly an array.

Methods inherited from class java.lang.Object

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

Field Detail

SEED

public static final int SEED

An initial value for a hashCode, to which we add contributions from fields. Using a non-zero value decreases collisions of hashCode values.

See Also:

Constant Field Values

PRIME

public static final int PRIME

The prime number used to multiply any calculated hashcode seed by i.e. result = PRIME*result + c Where result is the result of the previous calculation (at first this will be seed) and c is the calculated int to add to result

See Also:

Constant Field Values

Constructor Detail

Hashcoder

public Hashcoder()

Method Detail

hash

public static int hash(int seed,
                       boolean b)

hash

public static int hash(int seed,
                       char c)

hash

public static int hash(int seed,
                       int i)

Used for ints, bytes and shorts

hash

public static int hash(int seed,
                       long l)

long support done by shifting by 32 (using unsigned shift)

hash

public static int hash(int seed,
                       float f)

float support done via Float.floatToIntBits(float) which allows the encoding of a float as an int. We can then hash as normal.

hash

public static int hash(int seed,
                       double d)

double support which is done using the same techinque as float hashing except we convert to a long not to an int.

hash

public static int hash(int seed,
                       Object o)

o is a possibly-null object field, and possibly an array. If o is an array, then each element may be a primitive or a possibly-null object.