@XmlElement(value="expression") public interface Expression
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.
| Modifier and Type | Field and Description |
|---|---|
static Expression |
NIL
Constant expression that always evaulates to
null. |
| Modifier and Type | Method and Description |
|---|---|
Object |
accept(ExpressionVisitor visitor,
Object extraData)
Accepts a visitor.
|
Object |
evaluate(Object object)
Evaluates the given expression based on the content of the given object.
|
<T> T |
evaluate(Object object,
Class<T> context)
Evaluates the given expressoin based on the content of the given object and the context type.
|
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.
@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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