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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 }