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Complex event processing and event series analysis component

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/**************************************************************************************
 * Copyright (C) 2006-2015 EsperTech Inc. All rights reserved.                        *
 * http://www.espertech.com/esper                                                          *
 * http://www.espertech.com                                                           *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the GPL license       *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package com.espertech.esper.epl.spec;

import com.espertech.esper.epl.expression.core.ExprNode;
import com.espertech.esper.util.MetaDefItem;

import java.io.Serializable;
import java.util.Collection;

/**
 * Specification object to an element in the order-by expression.
 */
public class OrderByItem implements MetaDefItem, Serializable
{
    public static final OrderByItem[] EMPTY_ORDERBY_ARRAY = new OrderByItem[0];

    private ExprNode exprNode;
    private boolean isDescending;
    private static final long serialVersionUID = 4147598689501964350L;

    /**
     * Ctor.
     * @param exprNode is the order-by expression node
     * @param ascending is true for ascending, or false for descending sort
     */
    public OrderByItem(ExprNode exprNode, boolean ascending)
    {
        this.exprNode = exprNode;
        isDescending = ascending;
    }

    /**
     * Returns the order-by expression node.
     * @return expression node.
     */
    public ExprNode getExprNode()
    {
        return exprNode;
    }

    /**
     * Returns true for ascending, false for descending.
     * @return indicator if ascending or descending
     */
    public boolean isDescending()
    {
        return isDescending;
    }

    public OrderByItem copy() {
        return new OrderByItem(exprNode, isDescending());
    }

    public static OrderByItem[] toArray(Collection expressions) {
        if (expressions.isEmpty()) {
            return EMPTY_ORDERBY_ARRAY;
        }
        return expressions.toArray(new OrderByItem[expressions.size()]);
    }
}