001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.sequence;
018
019/**
020 * This interface should be implemented by user object to walk
021 * through {@link EditScript EditScript} objects.
022 * <p>
023 * Users should implement this interface in order to walk through
024 * the {@link EditScript EditScript} object created by the comparison
025 * of two sequences. This is a direct application of the visitor
026 * design pattern. The {@link EditScript#visit EditScript.visit}
027 * method takes an object implementing this interface as an argument,
028 * it will perform the loop over all commands in the script and the
029 * proper methods of the user class will be called as the commands are
030 * encountered.
031 * <p>
032 * The implementation of the user visitor class will depend on the
033 * need. Here are two examples.
034 * <p>
035 * The first example is a visitor that build the longest common
036 * subsequence:
037 * <pre>
038 * import org.apache.commons.collections4.comparators.sequence.CommandVisitor;
039 *
040 * import java.util.ArrayList;
041 *
042 * public class LongestCommonSubSequence implements CommandVisitor {
043 *
044 *   public LongestCommonSubSequence() {
045 *     a = new ArrayList();
046 *   }
047 *
048 *   public void visitInsertCommand(Object object) {
049 *   }
050 *
051 *   public void visitKeepCommand(Object object) {
052 *     a.add(object);
053 *   }
054 *
055 *   public void visitDeleteCommand(Object object) {
056 *   }
057 *
058 *   public Object[] getSubSequence() {
059 *     return a.toArray();
060 *   }
061 *
062 *   private ArrayList a;
063 *
064 * }
065 * </pre>
066 * <p>
067 * The second example is a visitor that shows the commands and the way
068 * they transform the first sequence into the second one:
069 * <pre>
070 * import org.apache.commons.collections4.comparators.sequence.CommandVisitor;
071 *
072 * import java.util.Arrays;
073 * import java.util.ArrayList;
074 * import java.util.Iterator;
075 *
076 * public class ShowVisitor implements CommandVisitor {
077 *
078 *   public ShowVisitor(Object[] sequence1) {
079 *     v = new ArrayList();
080 *     v.addAll(Arrays.asList(sequence1));
081 *     index = 0;
082 *   }
083 *
084 *   public void visitInsertCommand(Object object) {
085 *     v.insertElementAt(object, index++);
086 *     display("insert", object);
087 *   }
088 *
089 *   public void visitKeepCommand(Object object) {
090 *     ++index;
091 *     display("keep  ", object);
092 *   }
093 *
094 *   public void visitDeleteCommand(Object object) {
095 *     v.remove(index);
096 *     display("delete", object);
097 *   }
098 *
099 *   private void display(String commandName, Object object) {
100 *     System.out.println(commandName + " " + object + " -&gt;" + this);
101 *   }
102 *
103 *   public String toString() {
104 *     StringBuffer buffer = new StringBuffer();
105 *     for (Iterator iter = v.iterator(); iter.hasNext();) {
106 *       buffer.append(' ').append(iter.next());
107 *     }
108 *     return buffer.toString();
109 *   }
110 *
111 *   private ArrayList v;
112 *   private int index;
113 *
114 * }
115 * </pre>
116 *
117 * @since 4.0
118 */
119public interface CommandVisitor<T> {
120
121    /**
122     * Method called when an insert command is encountered.
123     *
124     * @param object object to insert (this object comes from the second sequence)
125     */
126    void visitInsertCommand(T object);
127
128    /**
129     * Method called when a keep command is encountered.
130     *
131     * @param object object to keep (this object comes from the first sequence)
132     */
133    void visitKeepCommand(T object);
134
135    /**
136     * Method called when a delete command is encountered.
137     *
138     * @param object object to delete (this object comes from the first sequence)
139     */
140    void visitDeleteCommand(T object);
141
142}