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.text.diff; 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 * <p> 033 * The implementation of the user visitor class will depend on the 034 * need. Here are two examples. 035 * </p> 036 * <p> 037 * The first example is a visitor that build the longest common 038 * subsequence: 039 * </p> 040 * <pre> 041 * import org.apache.commons.text.diff.CommandVisitor; 042 * 043 * import java.util.ArrayList; 044 * 045 * public class LongestCommonSubSequence implements CommandVisitor { 046 * 047 * public LongestCommonSubSequence() { 048 * a = new ArrayList(); 049 * } 050 * 051 * public void visitInsertCommand(Object object) { 052 * } 053 * 054 * public void visitKeepCommand(Object object) { 055 * a.add(object); 056 * } 057 * 058 * public void visitDeleteCommand(Object object) { 059 * } 060 * 061 * public Object[] getSubSequence() { 062 * return a.toArray(); 063 * } 064 * 065 * private ArrayList a; 066 * 067 * } 068 * </pre> 069 * <p> 070 * The second example is a visitor that shows the commands and the way 071 * they transform the first sequence into the second one: 072 * </p> 073 * <pre> 074 * import org.apache.commons.text.diff.CommandVisitor; 075 * 076 * import java.util.Arrays; 077 * import java.util.ArrayList; 078 * import java.util.Iterator; 079 * 080 * public class ShowVisitor implements CommandVisitor { 081 * 082 * public ShowVisitor(Object[] sequence1) { 083 * v = new ArrayList(); 084 * v.addAll(Arrays.asList(sequence1)); 085 * index = 0; 086 * } 087 * 088 * public void visitInsertCommand(Object object) { 089 * v.insertElementAt(object, index++); 090 * display("insert", object); 091 * } 092 * 093 * public void visitKeepCommand(Object object) { 094 * ++index; 095 * display("keep ", object); 096 * } 097 * 098 * public void visitDeleteCommand(Object object) { 099 * v.remove(index); 100 * display("delete", object); 101 * } 102 * 103 * private void display(String commandName, Object object) { 104 * System.out.println(commandName + " " + object + ": " + this); 105 * } 106 * 107 * public String toString() { 108 * StringBuffer buffer = new StringBuffer(); 109 * for (Iterator iter = v.iterator(); iter.hasNext();) { 110 * buffer.append(' ').append(iter.next()); 111 * } 112 * return buffer.toString(); 113 * } 114 * 115 * private ArrayList v; 116 * private int index; 117 * 118 * } 119 * </pre> 120 * 121 * @param <T> object type 122 * @since 1.0 123 */ 124public interface CommandVisitor<T> { 125 126 /** 127 * Method called when a delete command is encountered. 128 * 129 * @param object object to delete (this object comes from the first sequence) 130 */ 131 void visitDeleteCommand(T object); 132 133 /** 134 * Method called when an insert command is encountered. 135 * 136 * @param object object to insert (this object comes from the second sequence) 137 */ 138 void visitInsertCommand(T object); 139 140 /** 141 * Method called when a keep command is encountered. 142 * 143 * @param object object to keep (this object comes from the first sequence) 144 */ 145 void visitKeepCommand(T object); 146 147}