package com.malcom.library.android.utils.encoding;
import java.lang.reflect.Array;
/**
* 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>
*
* @author Malcom Ventures, S.L.
* @since 2012
*/
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)
{
// System.out.println("boolean...");
return firstTerm(aSeed) + (aBoolean ? 1 : 0);
}
/**
* chars.
*/
public static int hash(int aSeed, char aChar)
{
// System.out.println("char...");
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.
*/
// System.out.println("int...");
return firstTerm(aSeed) + aInt;
}
/**
* longs.
*/
public static int hash(int aSeed, long aLong)
{
// System.out.println("long...");
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();
}
}