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Types that extend and augment the Java Collections Framework.
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2001-2004 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowledgement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgement may appear in the software itself,
* if and wherever such third-party acknowledgements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact [email protected].
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* null objects.
**/
private Comparator nonNullComparator;
/**
* Specifies whether a null are compared as higher than
* non-null 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 {@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 {@link 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
**/
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 {@link 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.
**/
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 {@link 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
**/
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.
**/
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 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.
**/
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)));
}
private static final long serialVersionUID = -5820772575483504339L;
}