- /*
- * 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: 1.13 $ $Date: 2004/05/15 13:24:11 $
- *
- * @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)));
- }
-
- }