1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2025 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 * <div>
29 * Checks that sealed classes and interfaces have a permits list.
30 * </div>
31 *
32 * <p>
33 * Rationale: When a permits clause is omitted from a sealed class,
34 * any class within the same compilation unit can extend it. This differs
35 * from other sealed classes where permitted subclasses are explicitly
36 * declared, making them readily visible to the reader. Without a permits
37 * clause, identifying potential subclasses requires searching the entire
38 * compilation unit, which can be challenging, especially in large files
39 * with complex class hierarchies.
40 * </p>
41 *
42 * <p>
43 * See the <a href="https://docs.oracle.com/javase/specs/jls/se22/html/jls-13.html#jls-13.4.2">
44 * Java Language Specification</a> for more information about sealed classes.
45 * </p>
46 *
47 * @since 10.18.0
48 */
49
50 @StatelessCheck
51 public class SealedShouldHavePermitsListCheck extends AbstractCheck {
52
53 /**
54 * A key is pointing to the warning message text in "messages.properties"
55 * file.
56 */
57 public static final String MSG_KEY = "sealed.should.have.permits";
58
59 @Override
60 public int[] getDefaultTokens() {
61 return getRequiredTokens();
62 }
63
64 @Override
65 public int[] getAcceptableTokens() {
66 return getRequiredTokens();
67 }
68
69 @Override
70 public int[] getRequiredTokens() {
71 return new int[] {
72 TokenTypes.CLASS_DEF,
73 TokenTypes.INTERFACE_DEF,
74 };
75 }
76
77 @Override
78 public void visitToken(DetailAST ast) {
79 final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
80 final boolean isSealed = modifiers.findFirstToken(TokenTypes.LITERAL_SEALED) != null;
81 final boolean hasPermitsList = ast.findFirstToken(TokenTypes.PERMITS_CLAUSE) != null;
82
83 if (isSealed && !hasPermitsList) {
84 log(ast, MSG_KEY);
85 }
86 }
87 }