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 import java.util.stream.Collectors;
26
27 import com.puppycrawl.tools.checkstyle.StatelessCheck;
28 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
29 import com.puppycrawl.tools.checkstyle.api.DetailAST;
30 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
31
32 /**
33 * <div>
34 * Checks that all constructors are grouped together.
35 * If there is any non-constructor code separating constructors,
36 * this check identifies and logs a violation for those ungrouped constructors.
37 * The violation message will specify the line number of the last grouped constructor.
38 * Comments between constructors are allowed.
39 * </div>
40 *
41 * <p>
42 * Rationale: Grouping constructors together in a class improves code readability
43 * and maintainability. It allows developers to easily understand
44 * the different ways an object can be instantiated
45 * and the tasks performed by each constructor.
46 * </p>
47 *
48 * <p>
49 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
50 * </p>
51 *
52 * <p>
53 * Violation Message Keys:
54 * </p>
55 * <ul>
56 * <li>
57 * {@code constructors.declaration.grouping}
58 * </li>
59 * </ul>
60 *
61 * @since 10.17.0
62 */
63
64 @StatelessCheck
65 public class ConstructorsDeclarationGroupingCheck extends AbstractCheck {
66
67 /**
68 * A key is pointing to the warning message text in "messages.properties"
69 * file.
70 */
71 public static final String MSG_KEY = "constructors.declaration.grouping";
72
73 @Override
74 public int[] getDefaultTokens() {
75 return getRequiredTokens();
76 }
77
78 @Override
79 public int[] getAcceptableTokens() {
80 return getRequiredTokens();
81 }
82
83 @Override
84 public int[] getRequiredTokens() {
85 return new int[] {
86 TokenTypes.CLASS_DEF,
87 TokenTypes.ENUM_DEF,
88 TokenTypes.RECORD_DEF,
89 };
90 }
91
92 @Override
93 public void visitToken(DetailAST ast) {
94 // list of all child ASTs
95 final List<DetailAST> children = getChildList(ast);
96
97 // find first constructor
98 final DetailAST firstConstructor = children.stream()
99 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
100 .findFirst()
101 .orElse(null);
102
103 if (firstConstructor != null) {
104
105 // get all children AST after the first constructor
106 final List<DetailAST> childrenAfterFirstConstructor =
107 children.subList(children.indexOf(firstConstructor), children.size());
108
109 // find the first index of non-constructor AST after the first constructor, if present
110 final Optional<Integer> indexOfFirstNonConstructor = childrenAfterFirstConstructor
111 .stream()
112 .filter(currAst -> !isConstructor(currAst))
113 .findFirst()
114 .map(children::indexOf);
115
116 // list of all children after first non-constructor AST
117 final List<DetailAST> childrenAfterFirstNonConstructor = indexOfFirstNonConstructor
118 .map(index -> children.subList(index, children.size()))
119 .orElseGet(ArrayList::new);
120
121 // create a list of all constructors that are not grouped to log
122 final List<DetailAST> constructorsToLog = childrenAfterFirstNonConstructor.stream()
123 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
124 .collect(Collectors.toUnmodifiableList());
125
126 // find the last grouped constructor
127 final DetailAST lastGroupedConstructor = childrenAfterFirstConstructor.stream()
128 .takeWhile(ConstructorsDeclarationGroupingCheck::isConstructor)
129 .reduce((first, second) -> second)
130 .orElse(firstConstructor);
131
132 // log all constructors that are not grouped
133 constructorsToLog
134 .forEach(ctor -> log(ctor, MSG_KEY, lastGroupedConstructor.getLineNo()));
135 }
136 }
137
138 /**
139 * Get a list of all children of the given AST.
140 *
141 * @param ast the AST to get children of
142 * @return a list of all children of the given AST
143 */
144 private static List<DetailAST> getChildList(DetailAST ast) {
145 final List<DetailAST> children = new ArrayList<>();
146 DetailAST child = ast.findFirstToken(TokenTypes.OBJBLOCK).getFirstChild();
147 while (child != null) {
148 children.add(child);
149 child = child.getNextSibling();
150 }
151 return children;
152 }
153
154 /**
155 * Check if the given AST is a constructor.
156 *
157 * @param ast the AST to check
158 * @return true if the given AST is a constructor, false otherwise
159 */
160 private static boolean isConstructor(DetailAST ast) {
161 return ast.getType() == TokenTypes.CTOR_DEF
162 || ast.getType() == TokenTypes.COMPACT_CTOR_DEF;
163 }
164 }