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Java > Open Source Codes > org > apache > derby > impl > sql > compile > SubstituteExpressionVisitor


1 /*
2
3    Derby - Class org.apache.derby.impl.sql.compile.SubstituteExpressionVisitor
4
5    Licensed to the Apache Software Foundation (ASF) under one or more
6    contributor license agreements. See the NOTICE file distributed with
7    this work for additional information regarding copyright ownership.
8    The ASF licenses this file to you under the Apache License, Version 2.0
9    (the "License"); you may not use this file except in compliance with
10    the License. You may obtain a copy of the License at
11
12       http://www.apache.org/licenses/LICENSE-2.0
13
14    Unless required by applicable law or agreed to in writing, software
15    distributed under the License is distributed on an "AS IS" BASIS,
16    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17    See the License for the specific language governing permissions and
18    limitations under the License.
19
20  */
21 package org.apache.derby.impl.sql.compile;
22
23 import org.apache.derby.iapi.error.StandardException;
24 import org.apache.derby.iapi.sql.compile.Visitable;
25 import org.apache.derby.iapi.sql.compile.Visitor;
26
27 /**
28  * Replaces a <em>source</em> expression with a <em>target</em>
29  * expression.
30  *
31  * @author manish
32  */
33 class SubstituteExpressionVisitor implements Visitor
34 {
35     private ValueNode source;
36     private ValueNode target;
37     private Class JavaDoc skipOverClass;
38     
39     SubstituteExpressionVisitor(
40             ValueNode s, ValueNode t, Class JavaDoc skipThisClass)
41     {
42         source = s;
43         target = t;
44         skipOverClass = skipThisClass;
45     }
46
47     public Visitable visit(Visitable node) throws StandardException
48     {
49         if (!(node instanceof ValueNode))
50         {
51             return node;
52         }
53         
54         ValueNode nd = (ValueNode)node;
55         if (nd.isEquivalent(source))
56         {
57             return target;
58         }
59         else
60         {
61             return node;
62         }
63     }
64
65     public boolean stopTraversal()
66     {
67         return false;
68     }
69
70     public boolean skipChildren(Visitable node)
71     {
72         return (skipOverClass == null) ?
73                 false:
74                 skipOverClass.isInstance(node);
75     }
76 }
77
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