001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2019 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 com.puppycrawl.tools.checkstyle.StatelessCheck;
023import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
024import com.puppycrawl.tools.checkstyle.api.DetailAST;
025import com.puppycrawl.tools.checkstyle.api.TokenTypes;
026
027/**
028 * <p>Checks that string literals are not used with
029 * {@code ==} or <code>&#33;=</code>.
030 * </p>
031 * <p>
032 * Rationale: Novice Java programmers often use code like:
033 * </p>
034 * <pre>
035 * if (x == "something")
036 * </pre>
037 * <p>
038 * when they mean
039 * </p>
040 * <pre>
041 * if ("something".equals(x))
042 * </pre>
043 * <p>
044 * To configure the check:
045 * </p>
046 * <pre>
047 * &lt;module name=&quot;StringLiteralEquality&quot;/&gt;
048 * </pre>
049 *
050 * @since 3.2
051 * @noinspection HtmlTagCanBeJavadocTag
052 */
053@StatelessCheck
054public class StringLiteralEqualityCheck extends AbstractCheck {
055
056    /**
057     * A key is pointing to the warning message text in "messages.properties"
058     * file.
059     */
060    public static final String MSG_KEY = "string.literal.equality";
061
062    @Override
063    public int[] getDefaultTokens() {
064        return getRequiredTokens();
065    }
066
067    @Override
068    public int[] getAcceptableTokens() {
069        return getRequiredTokens();
070    }
071
072    @Override
073    public int[] getRequiredTokens() {
074        return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
075    }
076
077    @Override
078    public void visitToken(DetailAST ast) {
079        // no need to check for nulls here, == and != always have two children
080        final DetailAST firstChild = ast.getFirstChild();
081        final DetailAST secondChild = firstChild.getNextSibling();
082
083        if (firstChild.getType() == TokenTypes.STRING_LITERAL
084                || secondChild.getType() == TokenTypes.STRING_LITERAL) {
085            log(ast, MSG_KEY, ast.getText());
086        }
087    }
088
089}