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