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 * @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 @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.ENUM_DEF,
74 TokenTypes.RECORD_DEF,
75 };
76 }
77
78 @Override
79 public void visitToken(DetailAST ast) {
80 // list of all child ASTs
81 final List<DetailAST> children = getChildList(ast);
82
83 // find first constructor
84 final DetailAST firstConstructor = children.stream()
85 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
86 .findFirst()
87 .orElse(null);
88
89 if (firstConstructor != null) {
90
91 // get all children AST after the first constructor
92 final List<DetailAST> childrenAfterFirstConstructor =
93 children.subList(children.indexOf(firstConstructor), children.size());
94
95 // find the first index of non-constructor AST after the first constructor, if present
96 final Optional<Integer> indexOfFirstNonConstructor = childrenAfterFirstConstructor
97 .stream()
98 .filter(currAst -> !isConstructor(currAst))
99 .findFirst()
100 .map(children::indexOf);
101
102 // list of all children after first non-constructor AST
103 final List<DetailAST> childrenAfterFirstNonConstructor = indexOfFirstNonConstructor
104 .map(index -> children.subList(index, children.size()))
105 .orElseGet(ArrayList::new);
106
107 // create a list of all constructors that are not grouped to log
108 final List<DetailAST> constructorsToLog = childrenAfterFirstNonConstructor.stream()
109 .filter(ConstructorsDeclarationGroupingCheck::isConstructor)
110 .toList();
111
112 // find the last grouped constructor
113 final DetailAST lastGroupedConstructor = childrenAfterFirstConstructor.stream()
114 .takeWhile(ConstructorsDeclarationGroupingCheck::isConstructor)
115 .reduce((first, second) -> second)
116 .orElse(firstConstructor);
117
118 // log all constructors that are not grouped
119 constructorsToLog
120 .forEach(ctor -> log(ctor, MSG_KEY, lastGroupedConstructor.getLineNo()));
121 }
122 }
123
124 /**
125 * Get a list of all children of the given AST.
126 *
127 * @param ast the AST to get children of
128 * @return a list of all children of the given AST
129 */
130 private static List<DetailAST> getChildList(DetailAST ast) {
131 final List<DetailAST> children = new ArrayList<>();
132 DetailAST child = ast.findFirstToken(TokenTypes.OBJBLOCK).getFirstChild();
133 while (child != null) {
134 children.add(child);
135 child = child.getNextSibling();
136 }
137 return children;
138 }
139
140 /**
141 * Check if the given AST is a constructor.
142 *
143 * @param ast the AST to check
144 * @return true if the given AST is a constructor, false otherwise
145 */
146 private static boolean isConstructor(DetailAST ast) {
147 return ast.getType() == TokenTypes.CTOR_DEF
148 || ast.getType() == TokenTypes.COMPACT_CTOR_DEF;
149 }
150 }