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


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  * Represents a null literal expression.
40  */
41 public class NullLiteral extends Expr {
42   /**
43    * Create the literal.
44    */
45   public NullLiteral()
46   {
47   }
48
49   /**
50    * Returns true if the expression is constant.
51    */
52   @Override JavaDoc
53   public boolean isConstant()
54   {
55     return true;
56   }
57   
58   /**
59    * Evaluate the expression as an object.
60    *
61    * @param env the variable environment
62    *
63    * @return null
64    */
65   @Override JavaDoc
66   public Object JavaDoc getValue(ELContext env)
67     throws ELException
68   {
69     return null;
70   }
71
72   /**
73    * Evalutes directly to the output.
74    */
75   @Override JavaDoc
76   public boolean print(WriteStream out, ELContext env, boolean isEscaped)
77     throws IOException JavaDoc, ELException
78   {
79     return false;
80   }
81   
82   /**
83    * Prints the code to create an LongLiteral.
84    */
85   @Override JavaDoc
86   public void printCreate(WriteStream os)
87     throws IOException JavaDoc
88   {
89     os.print("new com.caucho.el.NullLiteral()");
90   }
91
92   /**
93    * Returns true for equal strings.
94    */
95   public boolean equals(Object JavaDoc o)
96   {
97     return (o instanceof NullLiteral);
98   }
99
100   /**
101    * Returns a printable view.
102    */
103   public String JavaDoc toString()
104   {
105     return "null";
106   }
107 }
108
109
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