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