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Java > Open Source Codes > com > caucho > el > AbstractBooleanExpr


1 /*
2  * Copyright (c) 1998-2006 Caucho Technology -- all rights reserved
3  *
4  * This file is part of Resin(R) Open Source
5  *
6  * Each copy or derived work must preserve the copyright notice and this
7  * notice unmodified.
8  *
9  * Resin Open Source is free software; you can redistribute it and/or modify
10  * it under the terms of the GNU General Public License as published by
11  * the Free Software Foundation; either version 2 of the License, or
12  * (at your option) any later version.
13  *
14  * Resin Open Source is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or any warranty
17  * of NON-INFRINGEMENT. See the GNU General Public License for more
18  * details.
19  *
20  * You should have received a copy of the GNU General Public License
21  * along with Resin Open Source; if not, write to the
22  *
23  * Free Software Foundation, Inc.
24  * 59 Temple Place, Suite 330
25  * Boston, MA 02111-1307 USA
26  *
27  * @author Scott Ferguson
28  */
29
30 package com.caucho.el;
31
32 import com.caucho.vfs.WriteStream;
33
34 import javax.el.ELContext;
35 import javax.el.ELException;
36 import java.io.IOException JavaDoc;
37
38 /**
39  * Base implementation for a boolean-valued expression.
40  */
41 abstract public class AbstractBooleanExpr extends Expr {
42   
43   /**
44    * Evaluate the expression as a boolean
45    *
46    * @param env the variable environment
47    *
48    * @return the value as a booleanstring
49    */
50   @Override JavaDoc
51   abstract public boolean evalBoolean(ELContext env)
52     throws ELException;
53   
54   /**
55    * Evaluate the expression as an object.
56    *
57    * @param env the variable environment
58    *
59    * @return the value as an object
60    */
61   @Override JavaDoc
62   public Object JavaDoc getValue(ELContext env)
63     throws ELException
64   {
65     return evalBoolean(env) ? Boolean.TRUE : Boolean.FALSE;
66   }
67   
68   /**
69    * Evaluate the expression as a string
70    *
71    * @param env the variable environment
72    *
73    * @return the value as a string
74    */
75   @Override JavaDoc
76   public String JavaDoc evalString(ELContext env)
77     throws ELException
78   {
79     return evalBoolean(env) ? "true" : "false";
80   }
81   
82   /**
83    * Evaluate the expression as a long
84    *
85    * @param env the variable environment
86    *
87    * @return the value as a long
88    */
89   @Override JavaDoc
90   public long evalLong(ELContext env)
91     throws ELException
92   {
93     ELException e = new ELException(L.l("'{0}': boolean expressions can not be converted to long values.", this));
94     
95     error(e, env);
96
97     return 0;
98   }
99   
100   /**
101    * Evaluate the expression as a double
102    */
103   @Override JavaDoc
104   public double evalDouble(ELContext env)
105     throws ELException
106   {
107     ELException e = new ELException(L.l("`{0}': boolean expressions can not be converted to double values.", this));
108     
109     error(e, env);
110
111     return 0;
112   }
113
114   /**
115    * Evalutes directly to the output.
116    *
117    * @param out the output stream
118    * @param env the variable environment
119    */
120   @Override JavaDoc
121   public boolean print(WriteStream out, ELContext env, boolean isEscaped)
122     throws IOException JavaDoc, ELException
123   {
124     if (evalBoolean(env))
125       out.print("true");
126     else
127       out.print("false");
128
129     return false;
130   }
131 }
132
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