001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2022 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 * To configure the check:
050 * </p>
051 * <pre>
052 * &lt;module name=&quot;StringLiteralEquality&quot;/&gt;
053 * </pre>
054 * <p>
055 * Examples of violations:
056 * </p>
057 * <pre>
058 * String status = "pending";
059 *
060 * if (status == "done") {} // violation
061 *
062 * while (status != "done") {} // violation
063 *
064 * boolean flag = (status == "done"); // violation
065 *
066 * boolean flag = (status.equals("done")); // OK
067 *
068 * String name = "X";
069 *
070 * if (name == getName()) {}
071 * // OK, limitation that check cannot tell runtime type returned from method call
072 * </pre>
073 * <p>
074 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
075 * </p>
076 * <p>
077 * Violation Message Keys:
078 * </p>
079 * <ul>
080 * <li>
081 * {@code string.literal.equality}
082 * </li>
083 * </ul>
084 *
085 * @since 3.2
086 * @noinspection HtmlTagCanBeJavadocTag
087 * @noinspectionreason HtmlTagCanBeJavadocTag - encoded symbols were not decoded
088 *      when replaced with Javadoc tag
089 */
090@StatelessCheck
091public class StringLiteralEqualityCheck extends AbstractCheck {
092
093    /**
094     * A key is pointing to the warning message text in "messages.properties"
095     * file.
096     */
097    public static final String MSG_KEY = "string.literal.equality";
098
099    @Override
100    public int[] getDefaultTokens() {
101        return getRequiredTokens();
102    }
103
104    @Override
105    public int[] getAcceptableTokens() {
106        return getRequiredTokens();
107    }
108
109    @Override
110    public int[] getRequiredTokens() {
111        return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
112    }
113
114    @Override
115    public void visitToken(DetailAST ast) {
116        final boolean hasStringLiteralChild =
117                ast.findFirstToken(TokenTypes.STRING_LITERAL) != null
118                    || ast.findFirstToken(TokenTypes.TEXT_BLOCK_LITERAL_BEGIN) != null
119                    || areStringsConcatenated(ast);
120
121        if (hasStringLiteralChild) {
122            log(ast, MSG_KEY, ast.getText());
123        }
124    }
125
126    /**
127     * Checks whether string literal or text block literals are concatenated.
128     *
129     * @param ast ast
130     * @return {@code true} if string literal or text block literals are concatenated
131     */
132    private static boolean areStringsConcatenated(DetailAST ast) {
133        DetailAST plusAst = ast.findFirstToken(TokenTypes.PLUS);
134        boolean result = false;
135        while (plusAst != null) {
136            if (plusAst.findFirstToken(TokenTypes.STRING_LITERAL) == null
137                    && plusAst.findFirstToken(TokenTypes.TEXT_BLOCK_LITERAL_BEGIN) == null) {
138                plusAst = plusAst.findFirstToken(TokenTypes.PLUS);
139            }
140            else {
141                result = true;
142                break;
143            }
144        }
145        return result;
146    }
147
148}