001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2024 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.checks.coding;
021
022import java.util.HashMap;
023import java.util.Map;
024
025import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
026import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
027import com.puppycrawl.tools.checkstyle.api.DetailAST;
028import com.puppycrawl.tools.checkstyle.api.FullIdent;
029import com.puppycrawl.tools.checkstyle.api.TokenTypes;
030import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
031
032/**
033 * <p>
034 * Checks that classes that either override {@code equals()} or {@code hashCode()} also
035 * overrides the other.
036 * This check only verifies that the method declarations match {@code Object.equals(Object)} and
037 * {@code Object.hashCode()} exactly to be considered an override. This check does not verify
038 * invalid method names, parameters other than {@code Object}, or anything else.
039 * </p>
040 * <p>
041 * Rationale: The contract of {@code equals()} and {@code hashCode()} requires that
042 * equal objects have the same hashCode. Therefore, whenever you override
043 * {@code equals()} you must override {@code hashCode()} to ensure that your class can
044 * be used in hash-based collections.
045 * </p>
046 * <p>
047 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
048 * </p>
049 * <p>
050 * Violation Message Keys:
051 * </p>
052 * <ul>
053 * <li>
054 * {@code equals.noEquals}
055 * </li>
056 * <li>
057 * {@code equals.noHashCode}
058 * </li>
059 * </ul>
060 *
061 * @since 3.0
062 */
063@FileStatefulCheck
064public class EqualsHashCodeCheck
065        extends AbstractCheck {
066
067    // implementation note: we have to use the following members to
068    // keep track of definitions in different inner classes
069
070    /**
071     * A key is pointing to the warning message text in "messages.properties"
072     * file.
073     */
074    public static final String MSG_KEY_HASHCODE = "equals.noHashCode";
075
076    /**
077     * A key is pointing to the warning message text in "messages.properties"
078     * file.
079     */
080    public static final String MSG_KEY_EQUALS = "equals.noEquals";
081
082    /** Maps OBJ_BLOCK to the method definition of equals(). */
083    private final Map<DetailAST, DetailAST> objBlockWithEquals = new HashMap<>();
084
085    /** Maps OBJ_BLOCKs to the method definition of hashCode(). */
086    private final Map<DetailAST, DetailAST> objBlockWithHashCode = new HashMap<>();
087
088    @Override
089    public int[] getDefaultTokens() {
090        return getRequiredTokens();
091    }
092
093    @Override
094    public int[] getAcceptableTokens() {
095        return getRequiredTokens();
096    }
097
098    @Override
099    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}