ArithmeticExpression


1   /*
2    * Copyright 2004-2005 Gary Bentley 
3    * 
4    * Licensed under the Apache License, Version 2.0 (the "License"); you may 
5    * not use this file except in compliance with the License. 
6    * You may obtain a copy of the License at 
7    *    http://www.apache.org/licenses/LICENSE-2.0 
8    *
9    * Unless required by applicable law or agreed to in writing, software 
10   * distributed under the License is distributed on an "AS IS" BASIS, 
11   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
12   * See the License for the specific language governing permissions and 
13   * limitations under the License.
14   */
15  package org.josql.expressions;
16  
17  import org.josql.Query;
18  import org.josql.QueryExecutionException;
19  import org.josql.QueryParseException;
20  
21  import org.josql.internal.Utilities;
22  
23  /**
24   * Represents the arithmetic expressions: *, +, /, - and %.
25   * It should be noted that ALL numbers in JoSQL are represented as <b>double</b> values, this
26   * allows for easy arithmetic operations without the fear of losing precision or casting
27   * issues.
28   * <p>
29   *  Last Modified By: $Author: barrygently $<br />
30   *  Last Modified On: $Date: 2004/12/20 16:22:43 $<br />
31   *  Current Revision: $Revision: 1.2 $<br />
32   */
33  public class ArithmeticExpression extends ValueExpression
34  {
35  
36      public static final int MULTIPLY = 0;
37      public static final int ADDITION = 1;
38      public static final int SUBTRACT = 2;
39      public static final int DIVIDE = 3;
40      public static final int MODULUS = 4;
41  
42      private int type = -1;
43  
44      private ValueExpression left = null;
45      private ValueExpression right = null;
46  
47      private boolean fixedResult = false;
48  
49      /**
50       * Return the expected return type.  This just returns the result of calling this
51       * method on the LHS.
52       *
53       * @param q The Query object.
54       * @return The expected return type class.
55       * @throws QueryParseException If something goes wrong in determining the return type.
56       */
57      public Class   getExpectedReturnType (Query  q)
58                                      throws QueryParseException
59      {
60  
61      return this.left.getExpectedReturnType (q);
62  
63      }
64  
65      /**
66       * Determine whether this arithmetic expression evaluates to true.
67       * Whilst this seems a little bizarre this method is needed to allow
68       * artithmetic expressions to be used in the columns part of the SELECT.
69       * <p>
70       * Thus the following could be performed:
71       * <pre>
72       *   SELECT 10 + 20
73       *   FROM   java.lang.Object
74       * </pre>
75       *
76       * The rules are as follows:
77       * <ul>
78       *   <li>If {@link #evaluate(Object,Query)} returns <code>null</code> then <code>false</code>
79       *       is returned.</li>
80       *   <li>If {@link #evaluate(Object,Query)} returns a number and it is greater than <b>0</b> then
81       *       <code>true</code> is returned.  If it is <b>0</b> or less than <b>0</b> 
82       *       then <code>false</code> is returned.
83       *   <li>If it is anything else then <code>true</code> is returned.
84       * </ul>
85       *
86       * @param o The object to perform the expression on.
87       * @param q The Query object.
88       * @return As according to the rules above.
89       * @throws QueryExecutionException If something goes wrong during the evaluation of the 
90       *                                 expression.
91       */
92      public boolean isTrue (Object   o,
93                 Query  q)
94                         throws QueryExecutionException
95      {
96  
97      o = this.evaluate (o,
98                 q);
99  
100     if (o == null)
101     {
102 
103         return false;
104 
105     }
106 
107     if (o instanceof Number  )
108     {
109 
110         return ((Number  ) o).doubleValue () > 0;
111 
112     }
113 
114     return true;
115 
116     }
117 
118     /**
119      * Return whether this expression has a fixed result. 
120      * 
121      * @param q The Query object.
122      * @return {@link Expression#hasFixedResult(Query) LHS.hasFixedResult(Query)} 
123      *         && 
124      *         {@link Expression#hasFixedResult(Query) RHS.hasFixedResult(Query)}
125      */
126     public boolean hasFixedResult (Query q)
127     {
128 
129     return this.fixedResult;
130 
131     }
132 
133     public void init (Query  q)
134                   throws QueryParseException
135     {
136 
137     this.left.init (q);
138     this.right.init (q);
139 
140     this.fixedResult = this.left.hasFixedResult (q) && this.right.hasFixedResult (q);
141 
142     }
143 
144     /**
145      * Get the RHS value expression.
146      *
147      * @return The RHS.
148      */
149     public ValueExpression getRight ()
150     {
151 
152     return this.right;
153 
154     }
155 
156     /**
157      * Get the LHS value expression.
158      *
159      * @return The LHS.
160      */
161     public ValueExpression getLeft ()
162     {
163 
164     return this.left;
165 
166     }
167 
168     public void setLeft (ValueExpression exp)
169     {
170 
171     this.left = exp;
172 
173     }
174 
175     public void setRight (ValueExpression exp)
176     {
177 
178     this.right = exp;
179 
180     }
181 
182     public int getType ()
183     {
184 
185     return this.type;
186 
187     }
188 
189     public void setType (int t)
190     {
191 
192     this.type = t;
193 
194     }
195 
196     /**
197      * Evaulate this expression.  Apart from the special cases the LHS and RHS must evaluate
198      * to an instance of <code>java.lang.Number</code> otherwise a QueryExecutionException is
199      * thrown.
200      * <p>
201      * Special cases:
202      * <ul>
203      *   <li>If the type of the expression is + and either LHS or RHS are NOT numbers 
204      *       then the String concatentation of them both are returned.  
205      *       This works the same as in Java.</li>
206      *   <li>If the type of the expression is / and the RHS is 0 then 0 is returned.</li>
207      * </ul>
208      *
209      * @param o The object to perform the expression on.
210      * @param q The Query object.
211      * @return The result of the expression, see the "special cases" for the exceptions to what would
212      *         be the intuitive result.
213      * @throws QueryExecutionException If an error occurs during processing.
214      */
215     public Object   evaluate (Object   o,
216                 Query  q)
217                         throws QueryExecutionException
218     {
219 
220     Object   l = this.left.getValue (o,
221                        q);
222 
223     Object   r = this.right.getValue (o,
224                     q);
225 
226     // Special case for addition.
227     if ((this.type == ArithmeticExpression.ADDITION)
228         &&
229         (!(l instanceof Number  )
230          ||
231          !(r instanceof Number  )
232         )
233        )
234     {
235 
236         StringBuffer   b = new StringBuffer   ();
237 
238         if (l == null)
239         {
240 
241         b.append ("null");
242 
243         } else {
244 
245         b.append (l);
246 
247         }
248 
249         if (r == null)
250         {
251 
252         b.append ("null");
253 
254         } else {
255 
256         b.append (r);
257 
258         }
259 
260         return b.toString ();
261 
262     }
263 
264     if (l == null)
265     {
266 
267         l = new Double   (0);
268 
269     }
270 
271     if (r == null)
272     {
273 
274         r = new Double   (0);
275 
276     }
277 
278     double ld = Utilities.getDouble (l);
279     double rd = Utilities.getDouble (r);
280 
281     if (this.type == ArithmeticExpression.ADDITION)
282     {
283 
284         return new Double   (ld + rd);
285 
286     }
287 
288     if (this.type == ArithmeticExpression.SUBTRACT)
289     {
290 
291         return new Double   (ld - rd);
292 
293     }
294 
295     if (this.type == ArithmeticExpression.MULTIPLY)
296     {
297 
298         return new Double   (ld * rd);
299 
300     }
301 
302     if (this.type == ArithmeticExpression.MODULUS)
303     {
304 
305         return new Double   (ld % rd);
306 
307     }
308 
309     if (this.type == ArithmeticExpression.DIVIDE)
310     {
311 
312         if (rd == 0)
313         {
314 
315         return new Double   (0);
316 
317         }
318 
319         return new Double   (ld / rd);
320 
321     }
322 
323     return null;
324 
325     }
326 
327     public String   toString ()
328     {
329 
330     String   pred = "+";
331     
332     if (this.type == ArithmeticExpression.MULTIPLY)
333     {
334 
335         pred = "*";
336 
337     }
338 
339     if (this.type == ArithmeticExpression.SUBTRACT)
340     {
341 
342         pred = "-";
343 
344     }
345 
346     if (this.type == ArithmeticExpression.MODULUS)
347     {
348 
349         pred = "%";
350 
351     }
352 
353     if (this.type == ArithmeticExpression.DIVIDE)
354     {
355 
356         pred = "/";
357 
358     }
359 
360     String   exp = this.left.toString () + " " + pred + " " + this.right.toString ();
361 
362     if (this.isBracketed ())
363     {
364 
365         exp = "(" + exp + ")";
366 
367     }
368 
369     return exp;
370 
371     }
372 
373 }
374
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