1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2024 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.HashMap;
23 import java.util.Map;
24
25 import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
26 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
27 import com.puppycrawl.tools.checkstyle.api.DetailAST;
28 import com.puppycrawl.tools.checkstyle.api.FullIdent;
29 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
30 import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
31
32 /**
33 * <div>
34 * Checks that classes that either override {@code equals()} or {@code hashCode()} also
35 * overrides the other.
36 * This check only verifies that the method declarations match {@code Object.equals(Object)} and
37 * {@code Object.hashCode()} exactly to be considered an override. This check does not verify
38 * invalid method names, parameters other than {@code Object}, or anything else.
39 * </div>
40 *
41 * <p>
42 * Rationale: The contract of {@code equals()} and {@code hashCode()} requires that
43 * equal objects have the same hashCode. Therefore, whenever you override
44 * {@code equals()} you must override {@code hashCode()} to ensure that your class can
45 * be used in hash-based collections.
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 equals.noEquals}
58 * </li>
59 * <li>
60 * {@code equals.noHashCode}
61 * </li>
62 * </ul>
63 *
64 * @since 3.0
65 */
66 @FileStatefulCheck
67 public class EqualsHashCodeCheck
68 extends AbstractCheck {
69
70 // implementation note: we have to use the following members to
71 // keep track of definitions in different inner classes
72
73 /**
74 * A key is pointing to the warning message text in "messages.properties"
75 * file.
76 */
77 public static final String MSG_KEY_HASHCODE = "equals.noHashCode";
78
79 /**
80 * A key is pointing to the warning message text in "messages.properties"
81 * file.
82 */
83 public static final String MSG_KEY_EQUALS = "equals.noEquals";
84
85 /** Maps OBJ_BLOCK to the method definition of equals(). */
86 private final Map<DetailAST, DetailAST> objBlockWithEquals = new HashMap<>();
87
88 /** Maps OBJ_BLOCKs to the method definition of hashCode(). */
89 private final Map<DetailAST, DetailAST> objBlockWithHashCode = new HashMap<>();
90
91 @Override
92 public int[] getDefaultTokens() {
93 return getRequiredTokens();
94 }
95
96 @Override
97 public int[] getAcceptableTokens() {
98 return getRequiredTokens();
99 }
100
101 @Override
102 public int[] getRequiredTokens() {
103 return new int[] {TokenTypes.METHOD_DEF};
104 }
105
106 @Override
107 public void beginTree(DetailAST rootAST) {
108 objBlockWithEquals.clear();
109 objBlockWithHashCode.clear();
110 }
111
112 @Override
113 public void visitToken(DetailAST ast) {
114 if (isEqualsMethod(ast)) {
115 objBlockWithEquals.put(ast.getParent(), ast);
116 }
117 else if (isHashCodeMethod(ast)) {
118 objBlockWithHashCode.put(ast.getParent(), ast);
119 }
120 }
121
122 /**
123 * Determines if an AST is a valid Equals method implementation.
124 *
125 * @param ast the AST to check
126 * @return true if the {code ast} is an Equals method.
127 */
128 private static boolean isEqualsMethod(DetailAST ast) {
129 final DetailAST modifiers = ast.getFirstChild();
130 final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
131
132 return CheckUtil.isEqualsMethod(ast)
133 && isObjectParam(parameters.getFirstChild())
134 && (ast.findFirstToken(TokenTypes.SLIST) != null
135 || modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
136 }
137
138 /**
139 * Determines if an AST is a valid HashCode method implementation.
140 *
141 * @param ast the AST to check
142 * @return true if the {code ast} is a HashCode method.
143 */
144 private static boolean isHashCodeMethod(DetailAST ast) {
145 final DetailAST modifiers = ast.getFirstChild();
146 final DetailAST methodName = ast.findFirstToken(TokenTypes.IDENT);
147 final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
148
149 return "hashCode".equals(methodName.getText())
150 && parameters.getFirstChild() == null
151 && (ast.findFirstToken(TokenTypes.SLIST) != null
152 || modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
153 }
154
155 /**
156 * Determines if an AST is a formal param of type Object.
157 *
158 * @param paramNode the AST to check
159 * @return true if firstChild is a parameter of an Object type.
160 */
161 private static boolean isObjectParam(DetailAST paramNode) {
162 final DetailAST typeNode = paramNode.findFirstToken(TokenTypes.TYPE);
163 final FullIdent fullIdent = FullIdent.createFullIdentBelow(typeNode);
164 final String name = fullIdent.getText();
165 return "Object".equals(name) || "java.lang.Object".equals(name);
166 }
167
168 @Override
169 public void finishTree(DetailAST rootAST) {
170 objBlockWithEquals
171 .entrySet().stream().filter(detailASTDetailASTEntry -> {
172 return objBlockWithHashCode.remove(detailASTDetailASTEntry.getKey()) == null;
173 }).forEach(detailASTDetailASTEntry -> {
174 final DetailAST equalsAST = detailASTDetailASTEntry.getValue();
175 log(equalsAST, MSG_KEY_HASHCODE);
176 });
177 objBlockWithHashCode.forEach((key, equalsAST) -> log(equalsAST, MSG_KEY_EQUALS));
178 }
179
180 }