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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 SequencesComparator.getScript method, the result is provided has a 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 
InsertCommand which correspond to an object of the second sequence being inserted into the first sequence, DeleteCommand which correspond to an object of the first sequence being removed and 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 Also:
SequencesComparator
EditScript
Since:
4.0/**
 * 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. /** Object on which the command should be applied. */
    private final T object;

    
Simple constructor. Creates a new instance of EditCommand
Params:
object –  reference to the object associated with this command, this
  refers to an element of one of the sequences being compared/**
     * 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.
Returns:
the object on which the command is applied/**
     * 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 EditScript, in order to implement the visitor design pattern 
Params:
visitor –  the visitor to be accepted/**
     * 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);

}