package org.hypergraphdb.util;
import java.lang.reflect.Array;
/**
* Collected methods which allow easy implementation of <code>hashCode</code>. Based on the recommendations of
* Effective Java, by Joshua Bloch.
*
* Example use case:
*
* <pre>
* public int hashCode() {
* int result = HashCodeUtil.SEED;
* //collect the contributions of various fields
* result = HashCodeUtil.hash(result, fPrimitive);
* result = HashCodeUtil.hash(result, fObject);
* result = HashCodeUtil.hash(result, fArray);
* return result;
* }
* </pre>
*/
public final class HashCodeUtil {
/**
* An initial value for a <code>hashCode</code>, to which is added contributions from fields. Using a
* non-zero value decreases collisions of <code>hashCode</code> values.
*/
public static final int SEED = 23;
/**
* booleans.
*/
public static int hash(int aSeed, boolean aBoolean) {
return firstTerm(aSeed) + (aBoolean ? 1 : 0);
}
/**
* chars.
*/
public static int hash(int aSeed, char aChar) {
return firstTerm(aSeed) + (int)aChar;
}
/**
* ints.
*/
public static int hash(int aSeed, int aInt) {
/*
* Implementation Note Note that byte and short are handled by this method, through implicit conversion.
*/
return firstTerm(aSeed) + aInt;
}
/**
* longs.
*/
public static int hash(int aSeed, long aLong) {
return firstTerm(aSeed) + (int)(aLong ^ (aLong >>> 32));
}
/**
* floats.
*/
public static int hash(int aSeed, float aFloat) {
return hash(aSeed, Float.floatToIntBits(aFloat));
}
/**
* doubles.
*/
public static int hash(int aSeed, double aDouble) {
return hash(aSeed, Double.doubleToLongBits(aDouble));
}
/**
* <code>aObject</code> is a possibly-null object field, and possibly an array.
*
* If <code>aObject</code> is an array, then each element may be a primitive or a possibly-null object.
*/
public static int hash(int aSeed, Object aObject) {
int result = aSeed;
if (aObject == null) {
result = hash(result, 0);
}
else if (!isArray(aObject)) {
result = hash(result, aObject.hashCode());
}
else {
int length = Array.getLength(aObject);
for (int idx = 0; idx < length; ++idx) {
Object item = Array.get(aObject, idx);
//recursive call!
result = hash(result, item);
}
}
return result;
}
/// PRIVATE ///
private static final int fODD_PRIME_NUMBER = 31;
private static int firstTerm(int aSeed) {
return fODD_PRIME_NUMBER * aSeed;
}
private static boolean isArray(Object aObject) {
return aObject.getClass().isArray();
}
}