1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2024 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 * <pre>
41 * if (x == "something")
42 * </pre>
43 *
44 * <p>
45 * when they mean
46 * </p>
47 * <pre>
48 * if ("something".equals(x))
49 * </pre>
50 *
51 * <p>
52 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
53 * </p>
54 *
55 * <p>
56 * Violation Message Keys:
57 * </p>
58 * <ul>
59 * <li>
60 * {@code string.literal.equality}
61 * </li>
62 * </ul>
63 *
64 * @since 3.2
65 * @noinspection HtmlTagCanBeJavadocTag
66 * @noinspectionreason HtmlTagCanBeJavadocTag - encoded symbols were not decoded
67 * when replaced with Javadoc tag
68 */
69 @StatelessCheck
70 public class StringLiteralEqualityCheck extends AbstractCheck {
71
72 /**
73 * A key is pointing to the warning message text in "messages.properties"
74 * file.
75 */
76 public static final String MSG_KEY = "string.literal.equality";
77
78 @Override
79 public int[] getDefaultTokens() {
80 return getRequiredTokens();
81 }
82
83 @Override
84 public int[] getAcceptableTokens() {
85 return getRequiredTokens();
86 }
87
88 @Override
89 public int[] getRequiredTokens() {
90 return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
91 }
92
93 @Override
94 public void visitToken(DetailAST ast) {
95 final boolean hasStringLiteralChild = hasStringLiteralChild(ast);
96
97 if (hasStringLiteralChild) {
98 log(ast, MSG_KEY, ast.getText());
99 }
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 }