org.nakedobjects.metamodel.commons.lang.HashCodeUtils Maven / Gradle / Ivy
package org.nakedobjects.metamodel.commons.lang;
import java.lang.reflect.Array;
/**
* Collected methods which allow easy implementation of hashCode, based on Josh Bloch's Effective
* Java.
*
*
* Example use case:
*
*
* 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;
* }
*
*
* @see http://www.javapractices.com/Topic28.cjp
*/
public final class HashCodeUtils {
private HashCodeUtils() {}
/**
* An initial value for a hashCode, to which is added contributions from fields. Using a
* non-zero value decreases collisons of hashCode values.
*/
public static final int SEED = 23;
/**
* booleans.
*/
public static int hash(final int aSeed, final boolean aBoolean) {
return firstTerm(aSeed) + (aBoolean ? 1 : 0);
}
/**
* chars.
*/
public static int hash(final int aSeed, final char aChar) {
return firstTerm(aSeed) + aChar;
}
/**
* ints.
*
*
* Note that byte and short are handled by this method, through implicit conversion.
*/
public static int hash(final int aSeed, final int aInt) {
return firstTerm(aSeed) + aInt;
}
/**
* longs.
*/
public static int hash(final int aSeed, final long aLong) {
return firstTerm(aSeed) + (int) (aLong ^ (aLong >>> 32));
}
/**
* floats.
*/
public static int hash(final int aSeed, final float aFloat) {
return hash(aSeed, Float.floatToIntBits(aFloat));
}
/**
* doubles.
*/
public static int hash(final int aSeed, final double aDouble) {
return hash(aSeed, Double.doubleToLongBits(aDouble));
}
/**
* aObject is a possibly-null object field, and possibly an array.
*
* If aObject is an array, then each element may be a primitive or a possibly-null object.
*/
public static int hash(final int aSeed, final Object aObject) {
int result = aSeed;
if (aObject == null) {
result = hash(result, 0);
} else if (!isArray(aObject)) {
result = hash(result, aObject.hashCode());
} else {
final int length = Array.getLength(aObject);
for (int idx = 0; idx < length; ++idx) {
final Object item = Array.get(aObject, idx);
// recursive call!
result = hash(result, item);
}
}
return result;
}
private static final int ODD_PRIME_NUMBER = 37;
private static int firstTerm(final int aSeed) {
return ODD_PRIME_NUMBER * aSeed;
}
private static boolean isArray(final Object aObject) {
return aObject.getClass().isArray();
}
}