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/*
* 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.collections4.sequence;
import java.util.ArrayList;
import java.util.List;
/**
* This class handles sequences of replacements resulting from a comparison.
*
* The comparison of two objects sequences leads to the identification of common
* parts and parts which only belong to the first or to the second sequence. The
* common parts appear in the edit script in the form of keep commands,
* they can be considered as synchronization objects between the two sequences.
* These synchronization objects split the two sequences in synchronized
* sub-sequences. The first sequence can be transformed into the second one by
* replacing each synchronized sub-sequence of the first sequence by the
* corresponding sub-sequence of the second sequence. This is a synthetic way to
* see an {@link EditScript edit script}, replacing individual
* {@link DeleteCommand delete}, {@link KeepCommand keep} and
* {@link InsertCommand insert} commands by fewer replacements acting on
* complete sub-sequences.
*
* This class is devoted to perform this interpretation. It visits an
* {@link EditScript edit script} (because it implements the
* {@link CommandVisitor CommandVisitor} interface) and calls a user-supplied
* handler implementing the {@link ReplacementsHandler ReplacementsHandler}
* interface to process the sub-sequences.
*
* @see ReplacementsHandler
* @see EditScript
* @see SequencesComparator
*
* @since 4.0
*/
public class ReplacementsFinder implements CommandVisitor {
private final List pendingInsertions;
private final List pendingDeletions;
private int skipped;
/** Handler to call when synchronized sequences are found. */
private final ReplacementsHandler handler;
/**
* Simple constructor. Creates a new instance of {@link ReplacementsFinder}.
*
* @param handler handler to call when synchronized sequences are found
*/
public ReplacementsFinder(final ReplacementsHandler handler) {
pendingInsertions = new ArrayList<>();
pendingDeletions = new ArrayList<>();
skipped = 0;
this.handler = handler;
}
/**
* Add an object to the pending insertions set.
*
* @param object object to insert
*/
@Override
public void visitInsertCommand(final T object) {
pendingInsertions.add(object);
}
/**
* Handle a synchronization object.
*
* When a synchronization object is identified, the pending insertions and
* pending deletions sets are provided to the user handler as subsequences.
*
* @param object synchronization object detected
*/
@Override
public void visitKeepCommand(final T object) {
if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
++skipped;
} else {
handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
pendingDeletions.clear();
pendingInsertions.clear();
skipped = 1;
}
}
/**
* Add an object to the pending deletions set.
*
* @param object object to delete
*/
@Override
public void visitDeleteCommand(final T object) {
pendingDeletions.add(object);
}
}