001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2018 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 antlr.collections.AST;
026import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
027import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
028import com.puppycrawl.tools.checkstyle.api.DetailAST;
029import com.puppycrawl.tools.checkstyle.api.FullIdent;
030import com.puppycrawl.tools.checkstyle.api.TokenTypes;
031import com.puppycrawl.tools.checkstyle.utils.CheckUtils;
032
033/**
034 * <p>
035 * Checks that classes that either override {@code equals()} or {@code hashCode()} also
036 * overrides the other.
037 * This checks only verifies that the method declarations match {@link Object#equals(Object)} and
038 * {@link Object#hashCode()} exactly to be considered an override. This check does not verify
039 * invalid method names, parameters other than {@code Object}, or anything else.
040 * </p>
041 * <p>
042 * Rationale: The contract of equals() and hashCode() requires that
043 * equal objects have the same hashCode. Hence, whenever you override
044 * equals() you must override hashCode() to ensure that your class can
045 * be used in collections that are hash based.
046 * </p>
047 * <p>
048 * An example of how to configure the check is:
049 * </p>
050 * <pre>
051 * &lt;module name="EqualsHashCode"/&gt;
052 * </pre>
053 * @author lkuehne
054 */
055@FileStatefulCheck
056public class EqualsHashCodeCheck
057        extends AbstractCheck {
058
059    // implementation note: we have to use the following members to
060    // keep track of definitions in different inner classes
061
062    /**
063     * A key is pointing to the warning message text in "messages.properties"
064     * file.
065     */
066    public static final String MSG_KEY_HASHCODE = "equals.noHashCode";
067
068    /**
069     * A key is pointing to the warning message text in "messages.properties"
070     * file.
071     */
072    public static final String MSG_KEY_EQUALS = "equals.noEquals";
073
074    /** Maps OBJ_BLOCK to the method definition of equals(). */
075    private final Map<DetailAST, DetailAST> objBlockWithEquals = new HashMap<>();
076
077    /** Maps OBJ_BLOCKs to the method definition of hashCode(). */
078    private final Map<DetailAST, DetailAST> objBlockWithHashCode = new HashMap<>();
079
080    @Override
081    public int[] getDefaultTokens() {
082        return getRequiredTokens();
083    }
084
085    @Override
086    public int[] getAcceptableTokens() {
087        return getRequiredTokens();
088    }
089
090    @Override
091    public int[] getRequiredTokens() {
092        return new int[] {TokenTypes.METHOD_DEF};
093    }
094
095    @Override
096    public void beginTree(DetailAST rootAST) {
097        objBlockWithEquals.clear();
098        objBlockWithHashCode.clear();
099    }
100
101    @Override
102    public void visitToken(DetailAST ast) {
103        if (isEqualsMethod(ast)) {
104            objBlockWithEquals.put(ast.getParent(), ast);
105        }
106        else if (isHashCodeMethod(ast)) {
107            objBlockWithHashCode.put(ast.getParent(), ast);
108        }
109    }
110
111    /**
112     * Determines if an AST is a valid Equals method implementation.
113     *
114     * @param ast the AST to check
115     * @return true if the {code ast} is a Equals method.
116     */
117    private static boolean isEqualsMethod(DetailAST ast) {
118        final DetailAST modifiers = ast.getFirstChild();
119        final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
120
121        return CheckUtils.isEqualsMethod(ast)
122                && modifiers.findFirstToken(TokenTypes.LITERAL_PUBLIC) != null
123                && isObjectParam(parameters.getFirstChild())
124                && (ast.findFirstToken(TokenTypes.SLIST) != null
125                        || modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
126    }
127
128    /**
129     * Determines if an AST is a valid HashCode method implementation.
130     *
131     * @param ast the AST to check
132     * @return true if the {code ast} is a HashCode method.
133     */
134    private static boolean isHashCodeMethod(DetailAST ast) {
135        final DetailAST modifiers = ast.getFirstChild();
136        final AST type = ast.findFirstToken(TokenTypes.TYPE);
137        final AST methodName = ast.findFirstToken(TokenTypes.IDENT);
138        final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
139
140        return type.getFirstChild().getType() == TokenTypes.LITERAL_INT
141                && "hashCode".equals(methodName.getText())
142                && modifiers.findFirstToken(TokenTypes.LITERAL_PUBLIC) != null
143                && modifiers.findFirstToken(TokenTypes.LITERAL_STATIC) == null
144                && parameters.getFirstChild() == null
145                && (ast.findFirstToken(TokenTypes.SLIST) != null
146                        || modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
147    }
148
149    /**
150     * Determines if an AST is a formal param of type Object.
151     * @param paramNode the AST to check
152     * @return true if firstChild is a parameter of an Object type.
153     */
154    private static boolean isObjectParam(DetailAST paramNode) {
155        final DetailAST typeNode = paramNode.findFirstToken(TokenTypes.TYPE);
156        final FullIdent fullIdent = FullIdent.createFullIdentBelow(typeNode);
157        final String name = fullIdent.getText();
158        return "Object".equals(name) || "java.lang.Object".equals(name);
159    }
160
161    @Override
162    public void finishTree(DetailAST rootAST) {
163        objBlockWithEquals
164            .entrySet().stream().filter(detailASTDetailASTEntry -> {
165                return objBlockWithHashCode.remove(detailASTDetailASTEntry.getKey()) == null;
166            }).forEach(detailASTDetailASTEntry -> {
167                final DetailAST equalsAST = detailASTDetailASTEntry.getValue();
168                log(equalsAST.getLineNo(), equalsAST.getColumnNo(), MSG_KEY_HASHCODE);
169            });
170        objBlockWithHashCode.forEach((key, equalsAST) -> {
171            log(equalsAST.getLineNo(), equalsAST.getColumnNo(), MSG_KEY_EQUALS);
172        });
173    }
174
175}