001 /*
002 * GeoAPI - Java interfaces for OGC/ISO standards
003 * http://www.geoapi.org
004 *
005 * Copyright (C) 2006-2012 Open Geospatial Consortium, Inc.
006 * All Rights Reserved. http://www.opengeospatial.org/ogc/legal
007 *
008 * Permission to use, copy, and modify this software and its documentation, with
009 * or without modification, for any purpose and without fee or royalty is hereby
010 * granted, provided that you include the following on ALL copies of the software
011 * and documentation or portions thereof, including modifications, that you make:
012 *
013 * 1. The full text of this NOTICE in a location viewable to users of the
014 * redistributed or derivative work.
015 * 2. Notice of any changes or modifications to the OGC files, including the
016 * date changes were made.
017 *
018 * THIS SOFTWARE AND DOCUMENTATION IS PROVIDED "AS IS," AND COPYRIGHT HOLDERS MAKE
019 * NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
020 * TO, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT
021 * THE USE OF THE SOFTWARE OR DOCUMENTATION WILL NOT INFRINGE ANY THIRD PARTY
022 * PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS.
023 *
024 * COPYRIGHT HOLDERS WILL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL OR
025 * CONSEQUENTIAL DAMAGES ARISING OUT OF ANY USE OF THE SOFTWARE OR DOCUMENTATION.
026 *
027 * The name and trademarks of copyright holders may NOT be used in advertising or
028 * publicity pertaining to the software without specific, written prior permission.
029 * Title to copyright in this software and any associated documentation will at all
030 * times remain with copyright holders.
031 */
032 package org.opengis.filter.expression;
033
034 import org.opengis.annotation.Extension;
035 import org.opengis.annotation.XmlElement;
036 import org.opengis.feature.Feature;
037
038
039 /**
040 * Interface for all the OGC Filter elements that compute values.
041 * <p>
042 * The most common use is with potentially using {@linkplain Feature feature} and
043 * metadata. The ability to access "attributes" based on the provided content is
044 * defined based on XPath queries currently.
045 *
046 * @version <A HREF="http://www.opengis.org/docs/02-059.pdf">Implementation specification 1.0</A>
047 * @author Chris Dillard (SYS Technologies)
048 * @author Justin Deoliveira (The Open Planning Project)
049 * @since GeoAPI 2.0
050 */
051 @XmlElement("expression")
052 public interface Expression {
053 /**
054 * Constant expression that always evaulates to {@code null}.
055 * <p>
056 * This constant is a "NullObject" that can represent the absense of
057 * expression in a data structures. As example it can be used to represent
058 * the default stroke color in a LineSymbolizer Stroke structure.
059 */
060 Expression NIL = new NilExpression();
061
062 /**
063 * Evaluates the given expression based on the content of the given object.
064 */
065 @Extension
066 Object evaluate(Object object);
067
068 /**
069 * Evaluates the given expressoin based on the content of the given object
070 * and the context type.
071 * <p>
072 * The {@code context} parameter is used to control the type of the
073 * result of the expression. A particular expression may not be able to evaluate
074 * to an instance of {@code context}. Therefore to be safe calling code
075 * should do a null check on the return value of this method, and call {@link #evaluate(Object)}
076 * if neccessary. Example:
077 * <pre>
078 * Object input = ...;
079 * String result = expression.evaluate( input, String.class );
080 * if ( result == null ) {
081 * result = expression.evalute( input ).toString();
082 * }
083 * ...
084 * </pre>
085 * </p>
086 * <p>
087 * Implementations that can not return a result as an instance of {@code context}
088 * should return {@code null}.
089 * </p>
090 * @param <T> The type of the returned object.
091 * @param object The object to evaluate the expression against.
092 * @param context The type of the resulting value of the expression.
093 *
094 * @return Evaluates the given expression based on the content of the given object an
095 * an instance of {@code context}.
096 */
097 @Extension
098 <T> T evaluate( Object object, Class<T> context );
099
100 /**
101 * Accepts a visitor. Subclasses must implement with a method whose content is the following:
102 * <pre>return visitor.{@linkplain ExpressionVisitor#visit visit}(this, extraData);</pre>
103 */
104 @Extension
105 Object accept(ExpressionVisitor visitor, Object extraData);
106 }