1 /** 2 * 3 * Copyright 2003-2004 The Apache Software Foundation 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 // 19 // This source code implements specifications defined by the Java 20 // Community Process. In order to remain compliant with the specification 21 // DO NOT add / change / or delete method signatures! 22 // 23 24 package javax.servlet.jsp.el; 25 26 27 /** 28 * <p>The abstract class for a prepared expression.</p> 29 * 30 * <p>An instance of an Expression can be obtained via from an 31 * ExpressionEvaluator instance.</p> 32 * 33 * <p>An Expression may or not have done a syntactic parse of the expression. 34 * A client invoking the evaluate() method should be ready for the case 35 * where ELParseException exceptions are raised. </p> 36 * 37 * @since 2.0 38 */ 39 public abstract class Expression { 40 41 /** 42 * Evaluates an expression that was previously prepared. In some 43 * implementations preparing an expression involves full syntactic 44 * validation, but others may not do so. Evaluating the expression may 45 * raise an ELParseException as well as other ELExceptions due to 46 * run-time evaluation. 47 * 48 * @param vResolver A VariableResolver instance that can be used at 49 * runtime to resolve the name of implicit objects into Objects. 50 * @return The result of the expression evaluation. 51 * 52 * @exception ELException Thrown if the expression evaluation failed. 53 */ 54 public abstract Object evaluate( VariableResolver vResolver ) 55 throws ELException; 56 } 57