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Java > Open Source Codes > org > apache > commons > jxpath > ri > compiler > CoreOperation


1 /*
2  * Copyright 1999-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
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 package org.apache.commons.jxpath.ri.compiler;
17
18 import org.apache.commons.jxpath.ri.EvalContext;
19
20 /**
21  * The common subclass for tree elements representing core operations like "+",
22  * "- ", "*" etc.
23  *
24  * @author Dmitri Plotnikov
25  * @version $Revision: 1.14 $ $Date: 2004/02/29 14:17:39 $
26  */
27 public abstract class CoreOperation extends Operation {
28         
29     public CoreOperation(Expression args[]) {
30         super(args);
31     }
32
33     public Object JavaDoc compute(EvalContext context) {
34         return computeValue(context);
35     }
36
37     public abstract Object JavaDoc computeValue(EvalContext context);
38     
39     /**
40      * Returns the XPath symbol for this operation, e.g. "+", "div", etc.
41      */
42     public abstract String JavaDoc getSymbol();
43     
44     /**
45      * Returns true if the operation is not sensitive to the order of arguments,
46      * e.g. "=", "and" etc, and false if it is, e.g. "<=", "div".
47      */
48     protected abstract boolean isSymmetric();
49     
50     /**
51      * Computes the precedence of the operation.
52      */
53     protected abstract int getPrecedence();
54     
55     public String JavaDoc toString() {
56         if (args.length == 1) {
57             return getSymbol() + parenthesize(args[0], false);
58         }
59         else {
60             StringBuffer JavaDoc buffer = new StringBuffer JavaDoc();
61             for (int i = 0; i < args.length; i++) {
62                 if (i > 0) {
63                     buffer.append(' ');
64                     buffer.append(getSymbol());
65                     buffer.append(' ');
66                 }
67                 buffer.append(parenthesize(args[i], i == 0));
68             }
69             return buffer.toString();
70         }
71     }
72     
73     private String JavaDoc parenthesize(Expression expression, boolean left) {
74         if (!(expression instanceof CoreOperation)) {
75             return expression.toString();
76         }
77         CoreOperation op = (CoreOperation) expression;
78         int myPrecedence = getPrecedence();
79         int thePrecedence = op.getPrecedence();
80
81         boolean needParens = true;
82         if (myPrecedence < thePrecedence) {
83             needParens = false;
84         }
85         else if (myPrecedence == thePrecedence) {
86             if (isSymmetric()) {
87                 needParens = false;
88             }
89             else {
90                 needParens = !left;
91             }
92         }
93
94         if (needParens) {
95             return "(" + expression.toString() + ")";
96         }
97         else {
98             return expression.toString();
99         }
100     }
101 }
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