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 * Abstract base class for all commands used to transform an objects sequence
021 * into another one.
022 * <p>
023 * When two objects sequences are compared through the
024 * {@link StringsComparator#getScript StringsComparator.getScript} method,
025 * the result is provided has a {@link EditScript script} containing the commands
026 * that progressively transform the first sequence into the second one.
027 * </p>
028 * <p>
029 * There are only three types of commands, all of which are subclasses of this
030 * abstract class. Each command is associated with one object belonging to at
031 * least one of the sequences. These commands are {@link InsertCommand
032 * InsertCommand} which correspond to an object of the second sequence being
033 * inserted into the first sequence, {@link DeleteCommand DeleteCommand} which
034 * correspond to an object of the first sequence being removed and
035 * {@link KeepCommand KeepCommand} which correspond to an object of the first
036 * sequence which {@code equals} an object in the second sequence. It is
037 * guaranteed that comparison is always performed this way (i.e. the
038 * {@code equals} method of the object from the first sequence is used and
039 * the object passed as an argument comes from the second sequence) ; this can
040 * be important if subclassing is used for some elements in the first sequence
041 * and the {@code equals} method is specialized.
042 * </p>
043 *
044 * <p>
045 * This code has been adapted from Apache Commons Collections 4.0.
046 * </p>
047 *
048 * @see StringsComparator
049 * @see EditScript
050 * @param <T> object type
051 * @since 1.0
052 */
053public abstract class EditCommand<T> {
054
055    /** Object on which the command should be applied. */
056    private final T object;
057
058    /**
059     * Constructs a new instance of EditCommand.
060     *
061     * @param object  reference to the object associated with this command, this
062     *   refers to an element of one of the sequences being compared
063     */
064    protected EditCommand(final T object) {
065        this.object = object;
066    }
067
068    /**
069     * Accepts a visitor.
070     * <p>
071     * This method is invoked for each commands belonging to
072     * an {@link EditScript EditScript}, in order to implement the visitor design pattern
073     * </p>
074     *
075     * @param visitor  the visitor to be accepted
076     */
077    public abstract void accept(CommandVisitor<T> visitor);
078
079    /**
080     * Gets the object associated with this command.
081     *
082     * @return The object on which the command is applied
083     */
084    protected T getObject() {
085        return object;
086    }
087
088}