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.coding;
21
22 import java.util.ArrayList;
23 import java.util.List;
24 import java.util.Optional;
25
26 import com.puppycrawl.tools.checkstyle.StatelessCheck;
27 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
28 import com.puppycrawl.tools.checkstyle.api.DetailAST;
29 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
30
31 /**
32 * <div>
33 * Checks that all constructors are grouped together.
34 * If there is any non-constructor code separating constructors,
35 * this check identifies and logs a violation for those ungrouped constructors.
36 * The violation message will specify the line number of the last grouped constructor.
37 * Comments between constructors are allowed.
38 * </div>
39 *
40 * <p>
41 * Rationale: Grouping constructors together in a class improves code readability
42 * and maintainability. It allows developers to easily understand
43 * the different ways an object can be instantiated
44 * and the tasks performed by each constructor.
45 * </p>
46 *
47 * <p>
48 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
49 * </p>
50 *
51 * <p>
52 * Violation Message Keys:
53 * </p>
54 * <ul>
55 * <li>
56 * {@code constructors.declaration.grouping}
57 * </li>
58 * </ul>
59 *
60 * @since 10.17.0
61 */
62
63 @StatelessCheck
64 public class ConstructorsDeclarationGroupingCheck extends AbstractCheck {
65
66 /**
67 * A key is pointing to the warning message text in "messages.properties"
68 * file.
69 */
70 public static final String MSG_KEY = "constructors.declaration.grouping";
71
72 @Override
73 public int[] getDefaultTokens() {
74 return getRequiredTokens();
75 }
76
77 @Override
78 public int[] getAcceptableTokens() {
79 return getRequiredTokens();
80 }
81
82 @Override
83 public int[] getRequiredTokens() {
84 return new int[] {
85 TokenTypes.CLASS_DEF,
86 TokenTypes.ENUM_DEF,
87 TokenTypes.RECORD_DEF,
88 };
89 }
90
91 @Override
92 public void visitToken(DetailAST ast) {
93 // list of all child ASTs
94 final List<DetailAST> children = getChildList(ast);
95
96 // find first constructor
97 final DetailAST firstConstructor = children.stream()
98 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
99 .findFirst()
100 .orElse(null);
101
102 if (firstConstructor != null) {
103
104 // get all children AST after the first constructor
105 final List<DetailAST> childrenAfterFirstConstructor =
106 children.subList(children.indexOf(firstConstructor), children.size());
107
108 // find the first index of non-constructor AST after the first constructor, if present
109 final Optional<Integer> indexOfFirstNonConstructor = childrenAfterFirstConstructor
110 .stream()
111 .filter(currAst -> !isConstructor(currAst))
112 .findFirst()
113 .map(children::indexOf);
114
115 // list of all children after first non-constructor AST
116 final List<DetailAST> childrenAfterFirstNonConstructor = indexOfFirstNonConstructor
117 .map(index -> children.subList(index, children.size()))
118 .orElseGet(ArrayList::new);
119
120 // create a list of all constructors that are not grouped to log
121 final List<DetailAST> constructorsToLog = childrenAfterFirstNonConstructor.stream()
122 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
123 .toList();
124
125 // find the last grouped constructor
126 final DetailAST lastGroupedConstructor = childrenAfterFirstConstructor.stream()
127 .takeWhile(ConstructorsDeclarationGroupingCheck::isConstructor)
128 .reduce((first, second) -> second)
129 .orElse(firstConstructor);
130
131 // log all constructors that are not grouped
132 constructorsToLog
133 .forEach(ctor -> log(ctor, MSG_KEY, lastGroupedConstructor.getLineNo()));
134 }
135 }
136
137 /**
138 * Get a list of all children of the given AST.
139 *
140 * @param ast the AST to get children of
141 * @return a list of all children of the given AST
142 */
143 private static List<DetailAST> getChildList(DetailAST ast) {
144 final List<DetailAST> children = new ArrayList<>();
145 DetailAST child = ast.findFirstToken(TokenTypes.OBJBLOCK).getFirstChild();
146 while (child != null) {
147 children.add(child);
148 child = child.getNextSibling();
149 }
150 return children;
151 }
152
153 /**
154 * Check if the given AST is a constructor.
155 *
156 * @param ast the AST to check
157 * @return true if the given AST is a constructor, false otherwise
158 */
159 private static boolean isConstructor(DetailAST ast) {
160 return ast.getType() == TokenTypes.CTOR_DEF
161 || ast.getType() == TokenTypes.COMPACT_CTOR_DEF;
162 }
163 }