org.apache.commons.collections4.sequence.EditCommand Maven / Gradle / Ivy
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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;
/**
* 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);
}