001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2024 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 * <pre>
041 * if (x == "something")
042 * </pre>
043 *
044 * <p>
045 * when they mean
046 * </p>
047 * <pre>
048 * if ("something".equals(x))
049 * </pre>
050 *
051 * <p>
052 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
053 * </p>
054 *
055 * <p>
056 * Violation Message Keys:
057 * </p>
058 * <ul>
059 * <li>
060 * {@code string.literal.equality}
061 * </li>
062 * </ul>
063 *
064 * @since 3.2
065 * @noinspection HtmlTagCanBeJavadocTag
066 * @noinspectionreason HtmlTagCanBeJavadocTag - encoded symbols were not decoded
067 *      when replaced with Javadoc tag
068 */
069@StatelessCheck
070public class StringLiteralEqualityCheck extends AbstractCheck {
071
072    /**
073     * A key is pointing to the warning message text in "messages.properties"
074     * file.
075     */
076    public static final String MSG_KEY = "string.literal.equality";
077
078    @Override
079    public int[] getDefaultTokens() {
080        return getRequiredTokens();
081    }
082
083    @Override
084    public int[] getAcceptableTokens() {
085        return getRequiredTokens();
086    }
087
088    @Override
089    public int[] getRequiredTokens() {
090        return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
091    }
092
093    @Override
094    public void visitToken(DetailAST ast) {
095        final boolean hasStringLiteralChild = hasStringLiteralChild(ast);
096
097        if (hasStringLiteralChild) {
098            log(ast, MSG_KEY, ast.getText());
099        }
100    }
101
102    /**
103     * Checks whether string literal or text block literals are concatenated.
104     *
105     * @param ast ast
106     * @return {@code true} if string literal or text block literals are concatenated
107     */
108    private static boolean hasStringLiteralChild(DetailAST ast) {
109        DetailAST currentAst = ast;
110        boolean result = false;
111        while (currentAst != null) {
112            if (currentAst.findFirstToken(TokenTypes.STRING_LITERAL) == null
113                    && currentAst.findFirstToken(TokenTypes.TEXT_BLOCK_LITERAL_BEGIN) == null) {
114                currentAst = currentAst.findFirstToken(TokenTypes.PLUS);
115            }
116            else {
117                result = true;
118                break;
119            }
120        }
121        return result;
122    }
123
124}