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 * <p>
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 * </p>
40 * <p>
41 * Rationale: The contract of {@code equals()} and {@code hashCode()} requires that
42 * equal objects have the same hashCode. Therefore, whenever you override
43 * {@code equals()} you must override {@code hashCode()} to ensure that your class can
44 * be used in hash-based collections.
45 * </p>
46 * <p>
47 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
48 * </p>
49 * <p>
50 * Violation Message Keys:
51 * </p>
52 * <ul>
53 * <li>
54 * {@code equals.noEquals}
55 * </li>
56 * <li>
57 * {@code equals.noHashCode}
58 * </li>
59 * </ul>
60 *
61 * @since 3.0
62 */
63 @FileStatefulCheck
64 public class EqualsHashCodeCheck
65 extends AbstractCheck {
66
67 // implementation note: we have to use the following members to
68 // keep track of definitions in different inner classes
69
70 /**
71 * A key is pointing to the warning message text in "messages.properties"
72 * file.
73 */
74 public static final String MSG_KEY_HASHCODE = "equals.noHashCode";
75
76 /**
77 * A key is pointing to the warning message text in "messages.properties"
78 * file.
79 */
80 public static final String MSG_KEY_EQUALS = "equals.noEquals";
81
82 /** Maps OBJ_BLOCK to the method definition of equals(). */
83 private final Map<DetailAST, DetailAST> objBlockWithEquals = new HashMap<>();
84
85 /** Maps OBJ_BLOCKs to the method definition of hashCode(). */
86 private final Map<DetailAST, DetailAST> objBlockWithHashCode = new HashMap<>();
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[] {TokenTypes.METHOD_DEF};
101 }
102
103 @Override
104 public void beginTree(DetailAST rootAST) {
105 objBlockWithEquals.clear();
106 objBlockWithHashCode.clear();
107 }
108
109 @Override
110 public void visitToken(DetailAST ast) {
111 if (isEqualsMethod(ast)) {
112 objBlockWithEquals.put(ast.getParent(), ast);
113 }
114 else if (isHashCodeMethod(ast)) {
115 objBlockWithHashCode.put(ast.getParent(), ast);
116 }
117 }
118
119 /**
120 * Determines if an AST is a valid Equals method implementation.
121 *
122 * @param ast the AST to check
123 * @return true if the {code ast} is an Equals method.
124 */
125 private static boolean isEqualsMethod(DetailAST ast) {
126 final DetailAST modifiers = ast.getFirstChild();
127 final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
128
129 return CheckUtil.isEqualsMethod(ast)
130 && isObjectParam(parameters.getFirstChild())
131 && (ast.findFirstToken(TokenTypes.SLIST) != null
132 || modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
133 }
134
135 /**
136 * Determines if an AST is a valid HashCode method implementation.
137 *
138 * @param ast the AST to check
139 * @return true if the {code ast} is a HashCode method.
140 */
141 private static boolean isHashCodeMethod(DetailAST ast) {
142 final DetailAST modifiers = ast.getFirstChild();
143 final DetailAST methodName = ast.findFirstToken(TokenTypes.IDENT);
144 final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
145
146 return "hashCode".equals(methodName.getText())
147 && parameters.getFirstChild() == null
148 && (ast.findFirstToken(TokenTypes.SLIST) != null
149 || modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
150 }
151
152 /**
153 * Determines if an AST is a formal param of type Object.
154 *
155 * @param paramNode the AST to check
156 * @return true if firstChild is a parameter of an Object type.
157 */
158 private static boolean isObjectParam(DetailAST paramNode) {
159 final DetailAST typeNode = paramNode.findFirstToken(TokenTypes.TYPE);
160 final FullIdent fullIdent = FullIdent.createFullIdentBelow(typeNode);
161 final String name = fullIdent.getText();
162 return "Object".equals(name) || "java.lang.Object".equals(name);
163 }
164
165 @Override
166 public void finishTree(DetailAST rootAST) {
167 objBlockWithEquals
168 .entrySet().stream().filter(detailASTDetailASTEntry -> {
169 return objBlockWithHashCode.remove(detailASTDetailASTEntry.getKey()) == null;
170 }).forEach(detailASTDetailASTEntry -> {
171 final DetailAST equalsAST = detailASTDetailASTEntry.getValue();
172 log(equalsAST, MSG_KEY_HASHCODE);
173 });
174 objBlockWithHashCode.forEach((key, equalsAST) -> log(equalsAST, MSG_KEY_EQUALS));
175 }
176
177 }