1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2026 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 import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
27
28 /**
29 * <div>
30 * Checks that each top-level class, interface, enum
31 * or annotation resides in a source file of its own.
32 * Official description of a 'top-level' term:
33 * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-7.html#jls-7.6">
34 * 7.6. Top Level Type Declarations</a>. If file doesn't contain
35 * public class, interface, enum or annotation, top-level type is the first type in file.
36 * </div>
37 *
38 * @since 5.8
39 */
40 @StatelessCheck
41 public class OneTopLevelClassCheck extends AbstractCheck {
42
43 /**
44 * A key is pointing to the warning message text in "messages.properties"
45 * file.
46 */
47 public static final String MSG_KEY = "one.top.level.class";
48
49 /**
50 * Creates a new {@code OneTopLevelClassCheck} instance.
51 */
52 public OneTopLevelClassCheck() {
53 // no code by default
54 }
55
56 @Override
57 public int[] getDefaultTokens() {
58 return getRequiredTokens();
59 }
60
61 @Override
62 public int[] getAcceptableTokens() {
63 return getRequiredTokens();
64 }
65
66 @Override
67 public int[] getRequiredTokens() {
68 return new int[] {
69 TokenTypes.COMPILATION_UNIT,
70 };
71 }
72
73 @Override
74 public void visitToken(DetailAST compilationUnit) {
75 DetailAST currentNode = compilationUnit.getFirstChild();
76
77 boolean publicTypeFound = false;
78 DetailAST firstType = null;
79
80 while (currentNode != null) {
81 if (isTypeDef(currentNode)) {
82 if (isPublic(currentNode)) {
83 // log the first type later
84 publicTypeFound = true;
85 }
86 if (firstType == null) {
87 // first type is set aside
88 firstType = currentNode;
89 }
90 else if (!isPublic(currentNode)) {
91 // extra non-public type, log immediately
92 final String typeName = currentNode
93 .findFirstToken(TokenTypes.IDENT).getText();
94 log(currentNode, MSG_KEY, typeName);
95 }
96 }
97 currentNode = currentNode.getNextSibling();
98 }
99
100 // if there was a public type and first type is non-public, log it
101 if (publicTypeFound && !isPublic(firstType)) {
102 final String typeName = firstType
103 .findFirstToken(TokenTypes.IDENT).getText();
104 log(firstType, MSG_KEY, typeName);
105 }
106 }
107
108 /**
109 * Checks if an AST node is a type definition.
110 *
111 * @param node AST node to check.
112 * @return true if the node is a type (class, enum, interface, annotation) definition.
113 */
114 private static boolean isTypeDef(DetailAST node) {
115 return TokenUtil.isTypeDeclaration(node.getType());
116 }
117
118 /**
119 * Checks if a type is public.
120 *
121 * @param typeDef type definition node.
122 * @return true if a type has a public access level modifier.
123 */
124 private static boolean isPublic(DetailAST typeDef) {
125 final DetailAST modifiers =
126 typeDef.findFirstToken(TokenTypes.MODIFIERS);
127 return modifiers.findFirstToken(TokenTypes.LITERAL_PUBLIC) != null;
128 }
129
130 }