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package javax.servlet.jsp.el;


/**
 * The abstract class for a prepared expression.
 *
 * An instance of an Expression can be obtained via from an 
 * ExpressionEvaluator instance.
 *
 * An Expression may or not have done a syntactic parse of the expression.
 * A client invoking the evaluate() method should be ready for the case 
 * where ELParseException exceptions are raised. 
 *
 * @deprecated As of JSP 2.1, replaced by {@link javax.el.ValueExpression}
 * @since JSP 2.0
 */
public abstract class Expression {

    /** 
     * Evaluates an expression that was previously prepared.  In some 
     * implementations preparing an expression involves full syntactic 
     * validation, but others may not do so.  Evaluating the expression may 
     * raise an ELParseException as well as other ELExceptions due to 
     * run-time evaluation.
     *
     * @param vResolver A VariableResolver instance that can be used at 
     *   runtime to resolve the name of implicit objects into Objects.
     * @return The result of the expression evaluation.
     *
     * @exception ELException Thrown if the expression evaluation failed.
     */ 
    public abstract Object evaluate( VariableResolver vResolver )
        throws ELException;
}