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