1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2024 the original author or authors.
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
20 package com.puppycrawl.tools.checkstyle.checks.design;
21
22 import com.puppycrawl.tools.checkstyle.StatelessCheck;
23 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
24 import com.puppycrawl.tools.checkstyle.api.DetailAST;
25 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
26
27 /**
28 * <p>
29 * Implements Joshua Bloch, Effective Java, Item 17 -
30 * Use Interfaces only to define types.
31 * </p>
32 * <p>
33 * According to Bloch, an interface should describe a <em>type</em>. It is therefore
34 * inappropriate to define an interface that does not contain any methods
35 * but only constants. The Standard interface
36 * <a href="https://docs.oracle.com/javase/8/docs/api/javax/swing/SwingConstants.html">
37 * javax.swing.SwingConstants</a> is an example of an interface that would be flagged by this check.
38 * </p>
39 * <p>
40 * The check can be configured to also disallow marker interfaces like {@code java.io.Serializable},
41 * that do not contain methods or constants at all.
42 * </p>
43 * <ul>
44 * <li>
45 * Property {@code allowMarkerInterfaces} - Control whether marker interfaces
46 * like Serializable are allowed.
47 * Type is {@code boolean}.
48 * Default value is {@code true}.
49 * </li>
50 * </ul>
51 * <p>
52 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
53 * </p>
54 * <p>
55 * Violation Message Keys:
56 * </p>
57 * <ul>
58 * <li>
59 * {@code interface.type}
60 * </li>
61 * </ul>
62 *
63 * @since 3.1
64 */
65 @StatelessCheck
66 public final class InterfaceIsTypeCheck
67 extends AbstractCheck {
68
69 /**
70 * A key is pointing to the warning message text in "messages.properties"
71 * file.
72 */
73 public static final String MSG_KEY = "interface.type";
74
75 /** Control whether marker interfaces like Serializable are allowed. */
76 private boolean allowMarkerInterfaces = true;
77
78 @Override
79 public int[] getDefaultTokens() {
80 return getRequiredTokens();
81 }
82
83 @Override
84 public int[] getRequiredTokens() {
85 return new int[] {TokenTypes.INTERFACE_DEF};
86 }
87
88 @Override
89 public int[] getAcceptableTokens() {
90 return getRequiredTokens();
91 }
92
93 @Override
94 public void visitToken(DetailAST ast) {
95 final DetailAST objBlock =
96 ast.findFirstToken(TokenTypes.OBJBLOCK);
97 final DetailAST methodDef =
98 objBlock.findFirstToken(TokenTypes.METHOD_DEF);
99 final DetailAST variableDef =
100 objBlock.findFirstToken(TokenTypes.VARIABLE_DEF);
101 final boolean methodRequired =
102 !allowMarkerInterfaces || variableDef != null;
103
104 if (methodDef == null && methodRequired) {
105 log(ast, MSG_KEY);
106 }
107 }
108
109 /**
110 * Setter to control whether marker interfaces like Serializable are allowed.
111 *
112 * @param flag whether to allow marker interfaces or not
113 * @since 3.1
114 */
115 public void setAllowMarkerInterfaces(boolean flag) {
116 allowMarkerInterfaces = flag;
117 }
118
119 }