1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2025 the original author or authors.
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ///////////////////////////////////////////////////////////////////////////////////////////////
19
20 package com.puppycrawl.tools.checkstyle.checks.coding;
21
22 import com.puppycrawl.tools.checkstyle.StatelessCheck;
23 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
24 import com.puppycrawl.tools.checkstyle.api.DetailAST;
25 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
26
27 /**
28 * <div>
29 * Checks that string literals are not used with <code>==</code> or <code>!=</code>.
30 * Since <code>==</code> will compare the object references, not the actual value of the strings,
31 * <code>String.equals()</code> should be used.
32 * More information can be found
33 * <a href="https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java/">
34 * in this article</a>.
35 * </div>
36 *
37 * <p>
38 * Rationale: Novice Java programmers often use code like:
39 * </p>
40 * <div class="wrapper"><pre class="prettyprint"><code class="language-java">
41 * if (x == "something")
42 * </code></pre></div>
43 *
44 * <p>
45 * when they mean
46 * </p>
47 * <div class="wrapper"><pre class="prettyprint"><code class="language-java">
48 * if ("something".equals(x))
49 * </code></pre></div>
50 *
51 * @since 3.2
52 * @noinspection HtmlTagCanBeJavadocTag
53 * @noinspectionreason HtmlTagCanBeJavadocTag - encoded symbols were not decoded
54 * when replaced with Javadoc tag
55 */
56 @StatelessCheck
57 public class StringLiteralEqualityCheck extends AbstractCheck {
58
59 /**
60 * A key is pointing to the warning message text in "messages.properties"
61 * file.
62 */
63 public static final String MSG_KEY = "string.literal.equality";
64
65 @Override
66 public int[] getDefaultTokens() {
67 return getRequiredTokens();
68 }
69
70 @Override
71 public int[] getAcceptableTokens() {
72 return getRequiredTokens();
73 }
74
75 @Override
76 public int[] getRequiredTokens() {
77 return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
78 }
79
80 @Override
81 public void visitToken(DetailAST ast) {
82 final boolean hasStringLiteralChild = hasStringLiteralChild(ast);
83
84 if (hasStringLiteralChild) {
85 log(ast, MSG_KEY, ast.getText());
86 }
87 }
88
89 /**
90 * Checks whether string literal or text block literals are concatenated.
91 *
92 * @param ast ast
93 * @return {@code true} if string literal or text block literals are concatenated
94 */
95 private static boolean hasStringLiteralChild(DetailAST ast) {
96 DetailAST currentAst = ast;
97 boolean result = false;
98 while (currentAst != null) {
99 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 }