/*

 * 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.

 * <p>

 * 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.

 * </p>

 * <p>

 * 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 <code>equals</code> an object in the second sequence. It is

 * guaranteed that comparison is always performed this way (i.e. the

 * <code>equals</code> 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 <code>equals</code> method is specialized.

 * </p>

 *

 * @see SequencesComparator

 * @see EditScript

 *

 * @since 4.0

 */

public abstract class EditCommand<T> {

    /** 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.

     * <p>

     * 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<T> visitor);

}