/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
Author: Michael A. Smith Since: Commons Collections 2.0 Version: $Revision: 647116 $ $Date: 2008-04-11 13:23:08 +0200 (Fri, 11 Apr 2008) $
/**
* A Comparator that will compare nulls to be either lower or higher than
* other objects.
*
* @since Commons Collections 2.0
* @version $Revision: 647116 $ $Date: 2008-04-11 13:23:08 +0200 (Fri, 11 Apr 2008) $
*
* @author Michael A. Smith
*/
public class NullComparator implements Comparator, Serializable {
Serialization version. /** Serialization version. */
private static final long serialVersionUID = -5820772575483504339L;
The comparator to use when comparing two non-null objects.
/**
* The comparator to use when comparing two non-<code>null</code> objects.
**/
private Comparator nonNullComparator;
Specifies whether a null are compared as higher than
non-null objects.
/**
* Specifies whether a <code>null</code> are compared as higher than
* non-<code>null</code> objects.
**/
private boolean nullsAreHigh;
//-----------------------------------------------------------------------
Construct an instance that sorts null higher than any
non-null object it is compared with. When comparing two
non-null objects, the ComparableComparator is used. /**
* 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 null higher than any
non-null object it is compared with. When comparing two
non-null objects, the specified Comparator is used. @param nonNullComparator the comparator to use when comparing two non-null objects. This argument cannot be
null
@exception NullPointerException if nonNullComparator is
null
/**
* 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 null higher or lower than
any non-null object it is compared with. When comparing
two non-null objects, the ComparableComparator is used. @param nullsAreHigh a true value indicates that
null should be compared as higher than a
non-null object. A false value indicates
that null should be compared as lower than a
non-null object.
/**
* 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 null higher or lower than
any non-null object it is compared with. When comparing
two non-null objects, the specified Comparator is used. @param nonNullComparator the comparator to use when comparing two non-null objects. This argument cannot be
null
@param nullsAreHigh a true value indicates that
null should be compared as higher than a
non-null object. A false value indicates
that null should be compared as lower than a
non-null object.
@exception NullPointerException if nonNullComparator is
null
/**
* 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
null, a 0 value is returned. If one object
is null 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 null, an
underlying comparator specified in the constructor (or the default) is
used to compare the non-null objects.
@param o1 the first object to compare
@param o2 the object to compare it to.
@return -1 if o1 is "lower" than (less than,
before, etc.) o2; 1 if o1 is
"higher" than (greater than, after, etc.) o2; or
0 if o1 and o2 are equal.
/**
* 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 equals(Object). @return a hash code for this comparator. /**
* 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 true if the specified object is a NullComparator
with equivalent null comparison behavior
(i.e. null high or low) and with equivalent underlying
non-null object comparators.
/**
* 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)));
}
}