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@XmlElement(value="expression") public interface Expression
Interface for all the OGC Filter elements that compute values.
The most common use is with potentially using feature and metadata. The ability to access "attributes" based on the provided content is defined based on XPath queries currently.
Field Summary | |
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static Expression |
NIL
Constant expression that always evaulates to null . |
Method Summary | ||
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Object |
accept(ExpressionVisitor visitor,
Object extraData)
Accepts a visitor. |
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Object |
evaluate(Object object)
Evaluates the given expression based on the content of the given object. |
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evaluate(Object object,
Class<T> context)
Evaluates the given expressoin based on the content of the given object and the context type. |
Field Detail |
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static final Expression NIL
null
.
This constant is a "NullObject" that can represent the absense of expression in a data structures. As example it can be used to represent the default stroke color in a LineSymbolizer Stroke structure.
Method Detail |
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@Extension Object evaluate(Object object)
@Extension <T> T evaluate(Object object, Class<T> context)
The context
parameter is used to control the type of the
result of the expression. A particular expression may not be able to evaluate
to an instance of context
. Therefore to be safe calling code
should do a null check on the return value of this method, and call evaluate(Object)
if neccessary. Example:
Object input = ...; String result = expression.evaluate( input, String.class ); if ( result == null ) { result = expression.evalute( input ).toString(); } ...
Implementations that can not return a result as an instance of context
should return null
.
T
- The type of the returned object.object
- The object to evaluate the expression against.context
- The type of the resulting value of the expression.
context
.@Extension Object accept(ExpressionVisitor visitor, Object extraData)
return visitor.visit(this, extraData);
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