01: /*
02: * Copyright 2004 The Apache Software Foundation
03: *
04: * Licensed under the Apache License, Version 2.0 (the "License");
05: * you may not use this file except in compliance with the License.
06: * You may obtain a copy of the License at
07: *
08: * http://www.apache.org/licenses/LICENSE-2.0
09: *
10: * Unless required by applicable law or agreed to in writing, software
11: * distributed under the License is distributed on an "AS IS" BASIS,
12: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13: * See the License for the specific language governing permissions and
14: * limitations under the License.
15: */
16:
17: package org.jbpm.jpdl.el;
18:
19: /**
20: * <p>The abstract class for a prepared expression.</p>
21: *
22: * <p>An instance of an Expression can be obtained via from an
23: * ExpressionEvaluator instance.</p>
24: *
25: * <p>An Expression may or not have done a syntactic parse of the expression.
26: * A client invoking the evaluate() method should be ready for the case
27: * where ELParseException exceptions are raised. </p>
28: *
29: * @since 2.0
30: */
31: public abstract class Expression {
32:
33: /**
34: * Evaluates an expression that was previously prepared. In some
35: * implementations preparing an expression involves full syntactic
36: * validation, but others may not do so. Evaluating the expression may
37: * raise an ELParseException as well as other ELExceptions due to
38: * run-time evaluation.
39: *
40: * @param vResolver A VariableResolver instance that can be used at
41: * runtime to resolve the name of implicit objects into Objects.
42: * @return The result of the expression evaluation.
43: *
44: * @exception ELException Thrown if the expression evaluation failed.
45: */
46: public abstract Object evaluate(VariableResolver vResolver)
47: throws ELException;
48: }
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