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
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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