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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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* http://www.apache.org/licenses/LICENSE-2.0
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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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package org.apache.commons.io.comparator;
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import java.io.Serializable;
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import java.util.Comparator;
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* Reverses the result of comparing two objects using
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* the delegate {@link Comparator}.
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* @version $Revision: 609243 $ $Date: 2008-01-06 00:30:42 +0000 (Sun, 06 Jan 2008) $
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* @since Commons IO 1.4
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class ReverseComparator implements Comparator, Serializable {
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private final Comparator delegate;
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* Construct an instance with the sepecified delegate {@link Comparator}.
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* @param delegate The comparator to delegate to
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public ReverseComparator(Comparator delegate) {
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if (delegate == null) {
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throw new IllegalArgumentException("Delegate comparator is missing");
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this.delegate = delegate;
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* Compare using the delegate Comparator, but reversing the result.
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* @param obj1 The first object to compare
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* @param obj2 The second object to compare
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* @return the result from the delegate {@link Comparator#compare(Object, Object)}
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* reversing the value (i.e. positive becomes negative and vice versa)
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public int compare(Object obj1, Object obj2) {
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return delegate.compare(obj2, obj1); // parameters switched round