/*
* Copyright 2001-2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections.comparators;
import java.io.Serializable;
import java.util.Comparator;
/**
* A Comparator that will compare nulls to be either lower or higher than
* other objects.
*
* @since Commons Collections 2.0
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @author Michael A. Smith
*/
public class NullComparator implements Comparator, Serializable {
/** Serialization version. */
private static final long serialVersionUID = -5820772575483504339L;
/**
* The comparator to use when comparing two non-<code>null</code> objects.
**/
private Comparator nonNullComparator;
/**
* Specifies whether a <code>null</code> are compared as higher than
* non-<code>null</code> objects.
**/
private boolean nullsAreHigh;
//-----------------------------------------------------------------------
/**
* Construct an instance that sorts <code>null</code> higher than any
* non-<code>null</code> object it is compared with. When comparing two
* non-<code>null</code> objects, the {@link ComparableComparator} is
* used.
**/
public NullComparator() {
this(ComparableComparator.getInstance(), true);
}
/**
* Construct an instance that sorts <code>null</code> higher than any
* non-<code>null</code> object it is compared with. When comparing two
* non-<code>null</code> objects, the specified {@link Comparator} is
* used.
*
* @param nonNullComparator the comparator to use when comparing two
* non-<code>null</code> objects. This argument cannot be
* <code>null</code>
*
* @exception NullPointerException if <code>nonNullComparator</code> is
* <code>null</code>
**/
public NullComparator(Comparator nonNullComparator) {
this(nonNullComparator, true);
}
/**
* Construct an instance that sorts <code>null</code> higher or lower than
* any non-<code>null</code> object it is compared with. When comparing
* two non-<code>null</code> objects, the {@link ComparableComparator} is
* used.
*
* @param nullsAreHigh a <code>true</code> value indicates that
* <code>null</code> should be compared as higher than a
* non-<code>null</code> object. A <code>false</code> value indicates
* that <code>null</code> should be compared as lower than a
* non-<code>null</code> object.
**/
public NullComparator(boolean nullsAreHigh) {
this(ComparableComparator.getInstance(), nullsAreHigh);
}
/**
* Construct an instance that sorts <code>null</code> higher or lower than
* any non-<code>null</code> object it is compared with. When comparing
* two non-<code>null</code> objects, the specified {@link Comparator} is
* used.
*
* @param nonNullComparator the comparator to use when comparing two
* non-<code>null</code> objects. This argument cannot be
* <code>null</code>
*
* @param nullsAreHigh a <code>true</code> value indicates that
* <code>null</code> should be compared as higher than a
* non-<code>null</code> object. A <code>false</code> value indicates
* that <code>null</code> should be compared as lower than a
* non-<code>null</code> object.
*
* @exception NullPointerException if <code>nonNullComparator</code> is
* <code>null</code>
**/
public NullComparator(Comparator nonNullComparator, boolean nullsAreHigh) {
this.nonNullComparator = nonNullComparator;
this.nullsAreHigh = nullsAreHigh;
if(nonNullComparator == null) {
throw new NullPointerException("null nonNullComparator");
}
}
//-----------------------------------------------------------------------
/**
* Perform a comparison between two objects. If both objects are
* <code>null</code>, a <code>0</code> value is returned. If one object
* is <code>null</code> and the other is not, the result is determined on
* whether the Comparator was constructed to have nulls as higher or lower
* than other objects. If neither object is <code>null</code>, an
* underlying comparator specified in the constructor (or the default) is
* used to compare the non-<code>null</code> objects.
*
* @param o1 the first object to compare
* @param o2 the object to compare it to.
* @return <code>-1</code> if <code>o1</code> is "lower" than (less than,
* before, etc.) <code>o2</code>; <code>1</code> if <code>o1</code> is
* "higher" than (greater than, after, etc.) <code>o2</code>; or
* <code>0</code> if <code>o1</code> and <code>o2</code> are equal.
**/
public int compare(Object o1, Object o2) {
if(o1 == o2) { return 0; }
if(o1 == null) { return (this.nullsAreHigh ? 1 : -1); }
if(o2 == null) { return (this.nullsAreHigh ? -1 : 1); }
return this.nonNullComparator.compare(o1, o2);
}
//-----------------------------------------------------------------------
/**
* Implement a hash code for this comparator that is consistent with
* {@link #equals(Object)}.
*
* @return a hash code for this comparator.
**/
public int hashCode() {
return (nullsAreHigh ? -1 : 1) * nonNullComparator.hashCode();
}
/**
* Determines whether the specified object represents a comparator that is
* equal to this comparator.
*
* @param obj the object to compare this comparator with.
*
* @return <code>true</code> if the specified object is a NullComparator
* with equivalent <code>null</code> comparison behavior
* (i.e. <code>null</code> high or low) and with equivalent underlying
* non-<code>null</code> object comparators.
**/
public boolean equals(Object obj) {
if(obj == null) { return false; }
if(obj == this) { return true; }
if(!obj.getClass().equals(this.getClass())) { return false; }
NullComparator other = (NullComparator)obj;
return ((this.nullsAreHigh == other.nullsAreHigh) &&
(this.nonNullComparator.equals(other.nonNullComparator)));
}
}