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Java > Open Source Codes > com > puppycrawl > tools > checkstyle > checks > design > HideUtilityClassConstructorCheck


1 ////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code for adherence to a set of rules.
3 // Copyright (C) 2001-2005 Oliver Burn
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ////////////////////////////////////////////////////////////////////////////////
19 package com.puppycrawl.tools.checkstyle.checks.design;
20
21 import com.puppycrawl.tools.checkstyle.api.Check;
22 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
23 import com.puppycrawl.tools.checkstyle.api.DetailAST;
24
25 /**
26  * Make sure that utility classes (classes that contain only static methods)
27  * do not have a public constructor.
28  * <p>
29  * Rationale: Instantiating utility classes does not make sense.
30  * A common mistake is forgetting to hide the default constructor.
31  * </p>
32  *
33  * @author lkuehne
34  * @version $Revision: 1.10 $
35  */
36 public class HideUtilityClassConstructorCheck extends Check
37 {
38     /** {@inheritDoc} */
39     public int[] getDefaultTokens()
40     {
41         return new int[] {TokenTypes.CLASS_DEF};
42     }
43
44     /** {@inheritDoc} */
45     public void visitToken(DetailAST aAST)
46     {
47         final DetailAST objBlock = aAST.findFirstToken(TokenTypes.OBJBLOCK);
48         DetailAST child = (DetailAST) objBlock.getFirstChild();
49         boolean hasMethod = false;
50         boolean hasNonStaticMethod = false;
51         boolean hasDefaultCtor = true;
52         boolean hasPublicCtor = false;
53
54         while (child != null) {
55             if (child.getType() == TokenTypes.METHOD_DEF) {
56                 hasMethod = true;
57                 final DetailAST modifiers =
58                     child.findFirstToken(TokenTypes.MODIFIERS);
59                 if (!modifiers.branchContains(TokenTypes.LITERAL_STATIC)) {
60                     hasNonStaticMethod = true;
61                 }
62             }
63             if (child.getType() == TokenTypes.CTOR_DEF) {
64                 hasDefaultCtor = false;
65                 final DetailAST modifiers =
66                     child.findFirstToken(TokenTypes.MODIFIERS);
67                 if (!modifiers.branchContains(TokenTypes.LITERAL_PRIVATE)
68                     && !modifiers.branchContains(TokenTypes.LITERAL_PROTECTED))
69                 {
70                     // treat package visible as public
71 // for the purpose of this Check
72 hasPublicCtor = true;
73                 }
74
75             }
76             child = (DetailAST) child.getNextSibling();
77         }
78
79         final boolean hasAccessibleCtor = (hasDefaultCtor || hasPublicCtor);
80
81         // figure out if class extends java.lang.object directly
82 // keep it simple for now and get a 99% solution
83 // TODO: check for "extends java.lang.Object" and "extends Object"
84 // consider "import org.omg.CORBA.*"
85 final boolean extendsJLO = // J.Lo even made it into in our sources :-)
86 aAST.findFirstToken(TokenTypes.EXTENDS_CLAUSE) == null;
87
88         if (extendsJLO
89                 && hasMethod && !hasNonStaticMethod && hasAccessibleCtor)
90         {
91             log(aAST.getLineNo(), aAST.getColumnNo(), "hide.utility.class");
92         }
93     }
94 }
95
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