001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 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 * <div>
029 * Checks that string literals are not used with <code>==</code> or <code>&#33;=</code>.
030 * Since <code>==</code> will compare the object references, not the actual value of the strings,
031 * <code>String.equals()</code> should be used.
032 * More information can be found
033 * <a href="https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java/">
034 * in this article</a>.
035 * </div>
036 *
037 * <p>
038 * Rationale: Novice Java programmers often use code like:
039 * </p>
040 * <div class="wrapper"><pre class="prettyprint"><code class="language-java">
041 * if (x == "something")
042 * </code></pre></div>
043 *
044 * <p>
045 * when they mean
046 * </p>
047 * <div class="wrapper"><pre class="prettyprint"><code class="language-java">
048 * if ("something".equals(x))
049 * </code></pre></div>
050 *
051 * @since 3.2
052 * @noinspection HtmlTagCanBeJavadocTag
053 * @noinspectionreason HtmlTagCanBeJavadocTag - encoded symbols were not decoded
054 *      when replaced with Javadoc tag
055 */
056@StatelessCheck
057public class StringLiteralEqualityCheck extends AbstractCheck {
058
059    /**
060     * A key is pointing to the warning message text in "messages.properties"
061     * file.
062     */
063    public static final String MSG_KEY = "string.literal.equality";
064
065    @Override
066    public int[] getDefaultTokens() {
067        return getRequiredTokens();
068    }
069
070    @Override
071    public int[] getAcceptableTokens() {
072        return getRequiredTokens();
073    }
074
075    @Override
076    public int[] getRequiredTokens() {
077        return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
078    }
079
080    @Override
081    public void visitToken(DetailAST ast) {
082        final boolean hasStringLiteralChild = hasStringLiteralChild(ast);
083
084        if (hasStringLiteralChild) {
085            log(ast, MSG_KEY, ast.getText());
086        }
087    }
088
089    /**
090     * Checks whether string literal or text block literals are concatenated.
091     *
092     * @param ast ast
093     * @return {@code true} if string literal or text block literals are concatenated
094     */
095    private static boolean hasStringLiteralChild(DetailAST ast) {
096        DetailAST currentAst = ast;
097        boolean result = false;
098        while (currentAst != null) {
099            if (currentAst.findFirstToken(TokenTypes.STRING_LITERAL) == null
100                    && currentAst.findFirstToken(TokenTypes.TEXT_BLOCK_LITERAL_BEGIN) == null) {
101                currentAst = currentAst.findFirstToken(TokenTypes.PLUS);
102            }
103            else {
104                result = true;
105                break;
106            }
107        }
108        return result;
109    }
110
111}