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/*****************************************************************************
* Copyright (c) 2014 Hewlett-Packard Development Company, L.P. and others. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0 which accompanies this distribution,
* and is available at http://www.eclipse.org/legal/epl-v10.html
*****************************************************************************/
package org.opendaylight.aaa;
import java.lang.reflect.Array;
/**
* Collected methods which allow easy implementation of <tt>hashCode</tt>.
*
* 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 <tt>hashCode</tt>, to which is added contributions
* from fields. Using a non-zero value decreases collisions of
* <tt>hashCode</tt> 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) + aChar;
}
/** ints. */
public static int hash(int aSeed, int aInt) {
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));
}
/**
* <tt>aObject</tt> is a possibly-null object field, and possibly an array.
*
* If <tt>aObject</tt> 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);
// if an item in the array references the array itself, prevent
// infinite looping
if (!(item == aObject)) {
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();
}
}
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