org.geotools.filter.expression
Class ExpressionAbstract

java.lang.Object
  org.geotools.filter.expression.ExpressionAbstract

All Implemented Interfaces:

org.opengis.filter.expression.Expression

Direct Known Subclasses:

DefaultExpression

public abstract class ExpressionAbstract

extends java.lang.Object

implements org.opengis.filter.expression.Expression

Abstract superclass of these Expression implementations.

Contains additional support for "Expression chaining". This allows Expressions to be constructed as a chain of Java commands similar to the use of the java collections api.

Note: Expression chaining is a simple developer convience, it has no effect on the data model exposed by the GeoAPI interfaces.

Idea: We may also be able to teach this implementation to make use of JXPath to extract "attribute values" from Java Beans, DOM, JDOM in addition to the geotools & geoapi FeatureType models. It is a cunning plan - any implementation will make use of this abstract base class.

Author:

Jody Garnett

Constructor Summary

ExpressionAbstract()

Method Summary

java.lang.Object	accept(org.opengis.filter.expression.ExpressionVisitor visitor, java.lang.Object extraData) Subclass should override, default implementation just returns extraData
protected java.lang.Object	eval(Expression expression, Feature feature) Helper method for subclasses to reduce null checks
java.lang.Object	evaluate(Feature feature) Subclass should overide, default implementation returns null
java.lang.Object	evaluate(java.lang.Object object) Subclass should overide, default implementation returns null

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExpressionAbstract

public ExpressionAbstract()

Method Detail

evaluate

public java.lang.Object evaluate(Feature feature)

Subclass should overide, default implementation returns null

evaluate

public java.lang.Object evaluate(java.lang.Object object)

Subclass should overide, default implementation returns null

Specified by:

evaluate in interface org.opengis.filter.expression.Expression

accept

public java.lang.Object accept(org.opengis.filter.expression.ExpressionVisitor visitor,
                               java.lang.Object extraData)

Subclass should override, default implementation just returns extraData

Specified by:

accept in interface org.opengis.filter.expression.Expression

eval

protected java.lang.Object eval(Expression expression,
                                Feature feature)

Helper method for subclasses to reduce null checks

Parameters:

expression -

feature -

Returns:

value or null