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.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 * @since 10.17.0
48 */
49
50 @StatelessCheck
51 public class ConstructorsDeclarationGroupingCheck 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 = "constructors.declaration.grouping";
58
59 /**
60 * A key is pointing to the warning message text in "messages.properties"
61 * file.
62 */
63 public static final String MSG_ORDER = "constructors.declaration.order";
64
65 /**
66 * Control whether to order constructors by increasing parameter count or not.
67 */
68 private boolean orderByIncreasingParameterCount;
69
70 /**
71 * Creates a new {@code ConstructorsDeclarationGroupingCheck} instance.
72 */
73 public ConstructorsDeclarationGroupingCheck() {
74 // no code by default
75 }
76
77 /**
78 * Setter to control whether to enforce order by increasing parameter count (arity) or not.
79 *
80 * @param orderByIncreasingParameterCount true if order by increasing parameter
81 * count is required.
82 * @since 13.6.0
83 */
84 public void setOrderByIncreasingParameterCount(boolean orderByIncreasingParameterCount) {
85 this.orderByIncreasingParameterCount = orderByIncreasingParameterCount;
86 }
87
88 @Override
89 public int[] getDefaultTokens() {
90 return getRequiredTokens();
91 }
92
93 @Override
94 public int[] getAcceptableTokens() {
95 return getRequiredTokens();
96 }
97
98 @Override
99 public int[] getRequiredTokens() {
100 return new int[] {
101 TokenTypes.CLASS_DEF,
102 TokenTypes.ENUM_DEF,
103 TokenTypes.RECORD_DEF,
104 };
105 }
106
107 @Override
108 public void visitToken(DetailAST ast) {
109 // list of all child ASTs
110 final List<DetailAST> children = getChildList(ast);
111
112 // find first constructor
113 final DetailAST firstConstructor = children.stream()
114 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
115 .findFirst()
116 .orElse(null);
117
118 if (firstConstructor != null) {
119
120 // get all children AST after the first constructor
121 final List<DetailAST> childrenAfterFirstConstructor =
122 children.subList(children.indexOf(firstConstructor), children.size());
123
124 // find the first index of non-constructor AST after the first constructor, if present
125 final Optional<Integer> indexOfFirstNonConstructor = childrenAfterFirstConstructor
126 .stream()
127 .filter(currAst -> !isConstructor(currAst))
128 .findFirst()
129 .map(children::indexOf);
130
131 // list of all children after first non-constructor AST
132 final List<DetailAST> childrenAfterFirstNonConstructor = indexOfFirstNonConstructor
133 .map(index -> children.subList(index, children.size()))
134 .orElseGet(ArrayList::new);
135
136 // create a list of all constructors that are not grouped to log
137 final List<DetailAST> constructorsToLog = childrenAfterFirstNonConstructor.stream()
138 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
139 .toList();
140
141 // find the last grouped constructor
142 final DetailAST lastGroupedConstructor = childrenAfterFirstConstructor.stream()
143 .takeWhile(ConstructorsDeclarationGroupingCheck::isConstructor)
144 .reduce((first, second) -> second)
145 .orElse(firstConstructor);
146
147 // log all constructors that are not grouped
148 constructorsToLog
149 .forEach(ctor -> log(ctor, MSG_KEY, lastGroupedConstructor.getLineNo()));
150
151 if (orderByIncreasingParameterCount) {
152
153 // list of all constructor ASTs
154 final List<DetailAST> allConstructors = children.stream()
155 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
156 .toList();
157
158 int previousParamCount = 0;
159 boolean isOrdered = true;
160 for (DetailAST constructor : allConstructors) {
161 final int currentParamCount = getParameterCount(constructor);
162 isOrdered = isOrdered && currentParamCount >= previousParamCount;
163 previousParamCount = currentParamCount;
164 if (!isOrdered) {
165 log(constructor, MSG_ORDER);
166 }
167 }
168 }
169 }
170 }
171
172 /**
173 * Get a list of all children of the given AST.
174 *
175 * @param ast the AST to get children of
176 * @return a list of all children of the given AST
177 */
178 private static List<DetailAST> getChildList(DetailAST ast) {
179 final List<DetailAST> children = new ArrayList<>();
180 DetailAST child = ast.findFirstToken(TokenTypes.OBJBLOCK).getFirstChild();
181 while (child != null) {
182 children.add(child);
183 child = child.getNextSibling();
184 }
185 return children;
186 }
187
188 /**
189 * Check if the given AST is a constructor.
190 *
191 * @param ast the AST to check
192 * @return true if the given AST is a constructor, false otherwise
193 */
194 private static boolean isConstructor(DetailAST ast) {
195 return ast.getType() == TokenTypes.CTOR_DEF
196 || ast.getType() == TokenTypes.COMPACT_CTOR_DEF;
197 }
198
199 /**
200 * Get the parameter count of a constructor.
201 *
202 * @param constructor the constructor AST
203 * @return the parameter count of the constructor
204 */
205 private static int getParameterCount(DetailAST constructor) {
206 final DetailAST params = constructor.findFirstToken(TokenTypes.PARAMETERS);
207 int parameterCount = 0;
208 if (params != null) {
209 parameterCount = params.getChildCount(TokenTypes.PARAMETER_DEF);
210 }
211 return parameterCount;
212 }
213
214 }