001 /** 002 * 003 * Copyright 2003-2004 The Apache Software Foundation 004 * 005 * Licensed under the Apache License, Version 2.0 (the "License"); 006 * you may not use this file except in compliance with the License. 007 * You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018 // 019 // This source code implements specifications defined by the Java 020 // Community Process. In order to remain compliant with the specification 021 // DO NOT add / change / or delete method signatures! 022 // 023 024 package javax.servlet.jsp.el; 025 026 027 /** 028 * <p>The abstract class for a prepared expression.</p> 029 * 030 * <p>An instance of an Expression can be obtained via from an 031 * ExpressionEvaluator instance.</p> 032 * 033 * <p>An Expression may or not have done a syntactic parse of the expression. 034 * A client invoking the evaluate() method should be ready for the case 035 * where ELParseException exceptions are raised. </p> 036 * 037 * @since 2.0 038 */ 039 public abstract class Expression { 040 041 /** 042 * Evaluates an expression that was previously prepared. In some 043 * implementations preparing an expression involves full syntactic 044 * validation, but others may not do so. Evaluating the expression may 045 * raise an ELParseException as well as other ELExceptions due to 046 * run-time evaluation. 047 * 048 * @param vResolver A VariableResolver instance that can be used at 049 * runtime to resolve the name of implicit objects into Objects. 050 * @return The result of the expression evaluation. 051 * 052 * @exception ELException Thrown if the expression evaluation failed. 053 */ 054 public abstract Object evaluate( VariableResolver vResolver ) 055 throws ELException; 056 } 057