Class ConstantExpression

  • All Implemented Interfaces:
    Cloneable, Expression, Literal
    Direct Known Subclasses:

    public class ConstantExpression
    extends Object
    implements Literal, Cloneable
    The Expression class is not immutable!

    However we do have a need for immutable literal expressions when defining our API for SLD, and any other standards based on Expression.

    Jody Garnett, Refractions Research
    • Constructor Detail

      • ConstantExpression

        protected ConstantExpression​(Object value)
      • ConstantExpression

        protected ConstantExpression​(short type,
                                     Object value)
    • Method Detail

      • evaluate

        public Object evaluate​(Object object)
        Description copied from interface: Expression
        Evaluates the given expression based on the content of the given object.
        Specified by:
        evaluate in interface Expression
        computed value
      • evaluate

        public <T> T evaluate​(Object object,
                              Class<T> context)
        Description copied from interface: Expression
        Evaluates the given expressoin based on the content of the given object and the context type.

        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 Expression.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.

        Specified by:
        evaluate in interface Expression
        Type Parameters:
        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.
        Evaluates the given expression based on the content of the given object an an instance of context.
      • getValue

        public Object getValue()
        Description copied from interface: Literal
        Returns the constant value held by this object.
        Specified by:
        getValue in interface Literal
      • setValue

        public void setValue​(Object constant)
      • accept

        public Object accept​(ExpressionVisitor visitor,
                             Object extraData)
        Description copied from interface: Expression
        Accepts a visitor. Subclasses must implement with a method whose content is the following:
        return visitor.visit(this, extraData);
        Specified by:
        accept in interface Expression
      • hashCode

        public int hashCode()
        hashCode in class Object