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Copy pathHashcoder.java
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126 lines (115 loc) · 3.24 KB
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/*
* BioJava development code
*
* This code may be freely distributed and modified under the
* terms of the GNU Lesser General Public Licence. This should
* be distributed with the code. If you do not have a copy,
* see:
*
* http://www.gnu.org/copyleft/lesser.html
*
* Copyright for this code is held jointly by the individual
* authors. These should be listed in @author doc comments.
*
* For more information on the BioJava project and its aims,
* or to join the biojava-l mailing list, visit the home page
* at:
*
* http://www.biojava.org/
*
*/
package org.biojava.nbio.core.util;
import java.lang.reflect.Array;
/**
* 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
*
* <pre>
* public int hashCode() {
* int result = Hashcoder.SEED;
* result = Hashcoder.hash(result, this.getName());
* result = Hashcoder.hash(result, this.getAge());
* return result;
* }
* </pre>
*
* @author ayates
*/
public class Hashcoder {
/**
* An initial value for a <code>hashCode</code>, to which we add
* contributions from fields. Using a non-zero value decreases collisions of
* <code>hashCode</code> values.
*/
public static final int SEED = 9;
/**
* 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
*/
public static final int PRIME = 79;
public static int hash(int seed, boolean b) {
return (PRIME * seed) + (b ? 1 : 0);
}
public static int hash(int seed, char c) {
return (PRIME * seed) + c;
}
/**
* Used for ints, bytes and shorts
*/
public static int hash(int seed, int i) {
return (PRIME * seed) + i;
}
/**
* long support done by shifting by 32 (using unsigned shift)
*/
public static int hash(int seed, long l) {
return (PRIME * seed) + (int) (l ^ (l >>> 32));
}
/**
* float support done via {@link Float#floatToIntBits(float)} which allows
* the encoding of a float as an int. We can then hash as normal.
*/
public static int hash(int seed, float f) {
return hash(seed, Float.floatToIntBits(f));
}
/**
* double support which is done using the same techinque as float hashing
* except we convert to a long not to an int.
*/
public static int hash(int seed, double d) {
return hash(seed, Double.doubleToLongBits(d));
}
/**
* <code>o</code> is a possibly-null object field, and possibly an
* array.
*
* If <code>o</code> is an array, then each element may be a primitive
* or a possibly-null object.
*/
public static int hash(int seed, Object o) {
int result = seed;
//If it was null then this is the result 0
if (o == null) {
result = hash(result, 0);
}
//If it wasn't an array then calculate the hashcode
else if (!o.getClass().isArray()) {
result = hash(result, o.hashCode());
}
//Otherwise loop &
else {
int length = Array.getLength(o);
for (int i = 0; i < length; i++) {
Object item = Array.get(o, i);
result = hash(result, item);// recursive call!
}
}
return result;
}
}