/**
*
* Funf: Open Sensing Framework
* Copyright (C) 2010-2011 Nadav Aharony, Wei Pan, Alex Pentland.
* Acknowledgments: Alan Gardner
* Contact: nadav@media.mit.edu
*
* This file is part of Funf.
*
* Funf is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 3 of
* the License, or (at your option) any later version.
*
* Funf is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
* See the GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with Funf. If not, see <http://www.gnu.org/licenses/>.
*
*/
package edu.mit.media.funf.util;
import java.lang.reflect.Array;
/**
* From Effective Java by Joshua Bloch
* Collected methods which allow easy implementation of <code>hashCode</code>.
*
* 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 collisons 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 = 37;
private static int firstTerm( int aSeed ){
return fODD_PRIME_NUMBER * aSeed;
}
private static boolean isArray(Object aObject){
return aObject.getClass().isArray();
}
}