org.apache.commons.collections4.sequence.package-info Maven / Gradle / Ivy
Show all versions of commons-collections4 Show documentation
/*
* 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.
*/
/**
* This package provides classes to compare two sequences of objects.
*
* The two sequences can hold any object type, as only the
* equals method is used to compare the elements of the
* sequences. It is guaranteed that the comparisons will always be done
* as o1.equals(o2) where o1 belongs to the
* first sequence and o2 belongs to the second
* sequence. This can be important if subclassing is used for some
* elements in the first sequence and the equals method is
* specialized.
*
* Comparison can be seen from two points of view: either as giving the
* smallest modification allowing to transform the first sequence into
* the second one, or as giving the longest sequence which is a
* subsequence of both initial sequences. The equals method
* is used to compare objects, so any object can be put into
* sequences. Modifications include deleting, inserting or keeping one
* object, starting from the beginning of the first sequence. Like most
* algorithms of the same type, objects transpositions are not
* supported. This means that if a sequence (A, B) is
* compared to (B, A), the result will be either the
* sequence of three commands delete A, keep B,
* insert A or the sequence insert B,
* keep A, delete B.
*
* The package uses a very efficient comparison algorithm designed by
* Eugene W. Myers and described in his paper: An O(ND)
* Difference Algorithm and Its Variations. This algorithm produces
* the shortest possible
* {@link org.apache.commons.collections4.sequence.EditScript edit script} containing
* all the {@link org.apache.commons.collections4.sequence.EditCommand commands}
* needed to transform the first sequence into the second one.
* The entry point for the user to this algorithm is the
* {@link org.apache.commons.collections4.sequence.SequencesComparator} class.
*
* As explained in Gene Myers paper, the edit script is equivalent to all
* other representations and contains all the needed information either
* to perform the transformation, of course, or to retrieve the longest
* common subsequence for example.
*
* If the user needs a very fine grained access to the comparison result,
* he needs to go through this script by providing a visitor implementing
* the {@link org.apache.commons.collections4.sequence.CommandVisitor} interface.
*
* Sometimes however, a more synthetic approach is needed. If the user
* prefers to see the differences between the two sequences as global
* replacement operations acting on complete subsequences of
* the original sequences, he will provide an object implementing the
* simple {@link org.apache.commons.collections4.sequence.ReplacementsHandler} interface,
* using an instance of the {@link org.apache.commons.collections4.sequence.ReplacementsFinder}
* class as a command converting layer between his object and the edit script. The number of
* objects which are common to both initial arrays and hence are skipped between each call to the user
* {@link org.apache.commons.collections4.sequence.ReplacementsHandler#handleReplacement handleReplacement}
* method is also provided. This allows the user to keep track of the current index in
* both arrays if he needs so.
*
* @version $Id: package-info.java 1479338 2013-05-05 15:21:44Z tn $
*/
package org.apache.commons.collections4.sequence;