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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.

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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
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 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.commons.collections4.sequence;

/**
 * Abstract base class for all commands used to transform an objects sequence
 * into another one.
 * 

* When two objects sequences are compared through the * {@link SequencesComparator#getScript SequencesComparator.getScript} method, * the result is provided has a {@link EditScript script} containing the commands * that progressively transform the first sequence into the second one. *

* There are only three types of commands, all of which are subclasses of this * abstract class. Each command is associated with one object belonging to at * least one of the sequences. These commands are {@link InsertCommand * InsertCommand} which correspond to an object of the second sequence being * inserted into the first sequence, {@link DeleteCommand DeleteCommand} which * correspond to an object of the first sequence being removed and * {@link KeepCommand KeepCommand} which correspond to an object of the first * sequence which equals an object in the second sequence. It is * guaranteed that comparison is always performed this way (i.e. the * equals method of the object from the first sequence is used and * the object passed as an argument comes from the second sequence) ; this can * be important if subclassing is used for some elements in the first sequence * and the equals method is specialized. * * @see SequencesComparator * @see EditScript * * @since 4.0 */ public abstract class EditCommand { /** Object on which the command should be applied. */ private final T object; /** * Simple constructor. Creates a new instance of EditCommand * * @param object reference to the object associated with this command, this * refers to an element of one of the sequences being compared */ protected EditCommand(final T object) { this.object = object; } /** * Returns the object associated with this command. * * @return the object on which the command is applied */ protected T getObject() { return object; } /** * Accept a visitor. *

* This method is invoked for each commands belonging to * an {@link EditScript EditScript}, in order to implement the visitor design pattern * * @param visitor the visitor to be accepted */ public abstract void accept(CommandVisitor visitor); }





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