EqualsHashCodeCheck.java
///////////////////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
// Copyright (C) 2001-2022 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
///////////////////////////////////////////////////////////////////////////////////////////////
package com.puppycrawl.tools.checkstyle.checks.coding;
import java.util.HashMap;
import java.util.Map;
import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.FullIdent;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
/**
* <p>
* Checks that classes that either override {@code equals()} or {@code hashCode()} also
* overrides the other.
* This check only verifies that the method declarations match {@code Object.equals(Object)} and
* {@code Object.hashCode()} exactly to be considered an override. This check does not verify
* invalid method names, parameters other than {@code Object}, or anything else.
* </p>
* <p>
* Rationale: The contract of {@code equals()} and {@code hashCode()} requires that
* equal objects have the same hashCode. Therefore, whenever you override
* {@code equals()} you must override {@code hashCode()} to ensure that your class can
* be used in hash-based collections.
* </p>
* <p>
* To configure the check:
* </p>
* <pre>
* <module name="EqualsHashCode"/>
* </pre>
* <p>Example:</p>
* <pre>
* public static class Example1 {
* public int hashCode() {
* // code
* }
* public boolean equals(String o) { // violation, overloaded implementation of 'equals'
* // code
* }
* }
* public static class Example2 {
* public boolean equals(Object o) { // violation, no 'hashCode'
* // code
* }
* public boolean equals(String o) {
* // code
* }
* }
* public static class Example3 {
* public int hashCode() {
* // code
* }
* public boolean equals(Object o) { // OK
* // code
* }
* public boolean equals(String o) {
* // code
* }
* }
* public static class Example4 {
* public int hashCode() {
* // code
* }
* public boolean equals(java.lang.Object o) { // OK
* // code
* }
* }
* public static class Example5 {
* public static int hashCode(int i) {
* // code
* }
* public boolean equals(Object o) { // violation, overloaded implementation of 'hashCode'
* // code
* }
* }
* public static class Example6 {
* public int hashCode() { // violation, overloaded implementation of 'equals'
* // code
* }
* public static boolean equals(Object o, Object o2) {
* // code
* }
* }
* </pre>
* <p>
* Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
* </p>
* <p>
* Violation Message Keys:
* </p>
* <ul>
* <li>
* {@code equals.noEquals}
* </li>
* <li>
* {@code equals.noHashCode}
* </li>
* </ul>
*
* @since 3.0
*/
@FileStatefulCheck
public class EqualsHashCodeCheck
extends AbstractCheck {
// implementation note: we have to use the following members to
// keep track of definitions in different inner classes
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_KEY_HASHCODE = "equals.noHashCode";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_KEY_EQUALS = "equals.noEquals";
/** Maps OBJ_BLOCK to the method definition of equals(). */
private final Map<DetailAST, DetailAST> objBlockWithEquals = new HashMap<>();
/** Maps OBJ_BLOCKs to the method definition of hashCode(). */
private final Map<DetailAST, DetailAST> objBlockWithHashCode = new HashMap<>();
@Override
public int[] getDefaultTokens() {
return getRequiredTokens();
}
@Override
public int[] getAcceptableTokens() {
return getRequiredTokens();
}
@Override
public int[] getRequiredTokens() {
return new int[] {TokenTypes.METHOD_DEF};
}
@Override
public void beginTree(DetailAST rootAST) {
objBlockWithEquals.clear();
objBlockWithHashCode.clear();
}
@Override
public void visitToken(DetailAST ast) {
if (isEqualsMethod(ast)) {
objBlockWithEquals.put(ast.getParent(), ast);
}
else if (isHashCodeMethod(ast)) {
objBlockWithHashCode.put(ast.getParent(), ast);
}
}
/**
* Determines if an AST is a valid Equals method implementation.
*
* @param ast the AST to check
* @return true if the {code ast} is an Equals method.
*/
private static boolean isEqualsMethod(DetailAST ast) {
final DetailAST modifiers = ast.getFirstChild();
final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
return CheckUtil.isEqualsMethod(ast)
&& isObjectParam(parameters.getFirstChild())
&& (ast.findFirstToken(TokenTypes.SLIST) != null
|| modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
}
/**
* Determines if an AST is a valid HashCode method implementation.
*
* @param ast the AST to check
* @return true if the {code ast} is a HashCode method.
*/
private static boolean isHashCodeMethod(DetailAST ast) {
final DetailAST modifiers = ast.getFirstChild();
final DetailAST methodName = ast.findFirstToken(TokenTypes.IDENT);
final DetailAST parameters = ast.findFirstToken(TokenTypes.PARAMETERS);
return "hashCode".equals(methodName.getText())
&& parameters.getFirstChild() == null
&& (ast.findFirstToken(TokenTypes.SLIST) != null
|| modifiers.findFirstToken(TokenTypes.LITERAL_NATIVE) != null);
}
/**
* Determines if an AST is a formal param of type Object.
*
* @param paramNode the AST to check
* @return true if firstChild is a parameter of an Object type.
*/
private static boolean isObjectParam(DetailAST paramNode) {
final DetailAST typeNode = paramNode.findFirstToken(TokenTypes.TYPE);
final FullIdent fullIdent = FullIdent.createFullIdentBelow(typeNode);
final String name = fullIdent.getText();
return "Object".equals(name) || "java.lang.Object".equals(name);
}
@Override
public void finishTree(DetailAST rootAST) {
objBlockWithEquals
.entrySet().stream().filter(detailASTDetailASTEntry -> {
return objBlockWithHashCode.remove(detailASTDetailASTEntry.getKey()) == null;
}).forEach(detailASTDetailASTEntry -> {
final DetailAST equalsAST = detailASTDetailASTEntry.getValue();
log(equalsAST, MSG_KEY_HASHCODE);
});
objBlockWithHashCode.forEach((key, equalsAST) -> log(equalsAST, MSG_KEY_EQUALS));
}
}