Copying from Collections to Lang
git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1154830 13f79535-47bb-0310-9956-ffa450edef68
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Henri Yandell
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.commons.collections.comparators;
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import java.io.Serializable;
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import java.util.Comparator;
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import org.apache.commons.collections.ComparatorUtils;
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/**
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* A Comparator that will compare nulls to be either lower or higher than
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* other objects.
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*
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* @since Commons Collections 2.0
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* @version $Revision$ $Date$
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*
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* @author Michael A. Smith
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*/
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public class NullComparator<E> implements Comparator<E>, Serializable {
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/** Serialization version. */
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private static final long serialVersionUID = -5820772575483504339L;
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/**
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* The comparator to use when comparing two non-<code>null</code> objects.
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**/
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private final Comparator<E> nonNullComparator;
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/**
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* Specifies whether a <code>null</code> are compared as higher than
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* non-<code>null</code> objects.
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**/
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private final boolean nullsAreHigh;
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//-----------------------------------------------------------------------
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/**
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* Construct an instance that sorts <code>null</code> higher than any
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* non-<code>null</code> object it is compared with. When comparing two
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* non-<code>null</code> objects, the {@link ComparableComparator} is
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* used.
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**/
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@SuppressWarnings("unchecked")
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public NullComparator() {
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this(ComparatorUtils.NATURAL_COMPARATOR, true);
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}
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/**
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* Construct an instance that sorts <code>null</code> higher than any
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* non-<code>null</code> object it is compared with. When comparing two
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* non-<code>null</code> objects, the specified {@link Comparator} is
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* used.
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*
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* @param nonNullComparator the comparator to use when comparing two
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* non-<code>null</code> objects. This argument cannot be
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* <code>null</code>
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*
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* @exception NullPointerException if <code>nonNullComparator</code> is
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* <code>null</code>
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**/
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public NullComparator(Comparator<E> nonNullComparator) {
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this(nonNullComparator, true);
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}
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/**
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* Construct an instance that sorts <code>null</code> higher or lower than
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* any non-<code>null</code> object it is compared with. When comparing
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* two non-<code>null</code> objects, the {@link ComparableComparator} is
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* used.
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*
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* @param nullsAreHigh a <code>true</code> value indicates that
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* <code>null</code> should be compared as higher than a
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* non-<code>null</code> object. A <code>false</code> value indicates
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* that <code>null</code> should be compared as lower than a
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* non-<code>null</code> object.
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**/
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@SuppressWarnings("unchecked")
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public NullComparator(boolean nullsAreHigh) {
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this(ComparatorUtils.NATURAL_COMPARATOR, nullsAreHigh);
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}
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/**
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* Construct an instance that sorts <code>null</code> higher or lower than
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* any non-<code>null</code> object it is compared with. When comparing
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* two non-<code>null</code> objects, the specified {@link Comparator} is
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* used.
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*
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* @param nonNullComparator the comparator to use when comparing two
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* non-<code>null</code> objects. This argument cannot be
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* <code>null</code>
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*
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* @param nullsAreHigh a <code>true</code> value indicates that
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* <code>null</code> should be compared as higher than a
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* non-<code>null</code> object. A <code>false</code> value indicates
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* that <code>null</code> should be compared as lower than a
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* non-<code>null</code> object.
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*
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* @exception NullPointerException if <code>nonNullComparator</code> is
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* <code>null</code>
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**/
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public NullComparator(Comparator<E> nonNullComparator, boolean nullsAreHigh) {
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this.nonNullComparator = nonNullComparator;
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this.nullsAreHigh = nullsAreHigh;
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if (nonNullComparator == null) {
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throw new NullPointerException("null nonNullComparator");
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}
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}
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//-----------------------------------------------------------------------
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/**
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* Perform a comparison between two objects. If both objects are
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* <code>null</code>, a <code>0</code> value is returned. If one object
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* is <code>null</code> and the other is not, the result is determined on
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* whether the Comparator was constructed to have nulls as higher or lower
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* than other objects. If neither object is <code>null</code>, an
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* underlying comparator specified in the constructor (or the default) is
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* used to compare the non-<code>null</code> objects.
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*
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* @param o1 the first object to compare
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* @param o2 the object to compare it to.
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* @return <code>-1</code> if <code>o1</code> is "lower" than (less than,
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* before, etc.) <code>o2</code>; <code>1</code> if <code>o1</code> is
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* "higher" than (greater than, after, etc.) <code>o2</code>; or
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* <code>0</code> if <code>o1</code> and <code>o2</code> are equal.
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**/
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public int compare(E o1, E o2) {
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if(o1 == o2) { return 0; }
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if(o1 == null) { return (this.nullsAreHigh ? 1 : -1); }
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if(o2 == null) { return (this.nullsAreHigh ? -1 : 1); }
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return this.nonNullComparator.compare(o1, o2);
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}
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//-----------------------------------------------------------------------
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/**
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* Implement a hash code for this comparator that is consistent with
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* {@link #equals(Object)}.
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*
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* @return a hash code for this comparator.
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**/
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@Override
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public int hashCode() {
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return (nullsAreHigh ? -1 : 1) * nonNullComparator.hashCode();
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}
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/**
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* Determines whether the specified object represents a comparator that is
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* equal to this comparator.
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*
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* @param obj the object to compare this comparator with.
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*
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* @return <code>true</code> if the specified object is a NullComparator
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* with equivalent <code>null</code> comparison behavior
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* (i.e. <code>null</code> high or low) and with equivalent underlying
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* non-<code>null</code> object comparators.
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**/
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@Override
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public boolean equals(Object obj) {
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if(obj == null) { return false; }
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if(obj == this) { return true; }
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if(!obj.getClass().equals(this.getClass())) { return false; }
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NullComparator<?> other = (NullComparator<?>) obj;
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return ((this.nullsAreHigh == other.nullsAreHigh) &&
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(this.nonNullComparator.equals(other.nonNullComparator)));
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}
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}
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