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;
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> Checks that hexadecimal literals are defined using uppercase letters {@code (A-F)}
29 * rather than lowercase {@code (a-f)}.
30 * This convention follows the
31 * <a href="https://cr.openjdk.org/~alundblad/styleguide/index-v6.html#toc-literals">
32 * OpenJDK Style Guide</a>.
33 * </div>
34 *
35 * @since 12.1.0
36 */
37 @StatelessCheck
38 public class HexLiteralCaseCheck extends AbstractCheck {
39
40 /**
41 * A key is pointing to the warning message text in "messages.properties"
42 * file.
43 */
44 public static final String MSG_KEY = "hex.literal";
45
46 /** ASCII value for lowercase 'a'. */
47 private static final int A_ASCII = 97;
48
49 /** ASCII value for lowercase 'f'. */
50 private static final int F_ASCII = 102;
51
52 @Override
53 public int[] getDefaultTokens() {
54 return getRequiredTokens();
55 }
56
57 @Override
58 public int[] getAcceptableTokens() {
59 return getRequiredTokens();
60 }
61
62 @Override
63 public int[] getRequiredTokens() {
64 return new int[] {TokenTypes.NUM_LONG, TokenTypes.NUM_INT};
65 }
66
67 @Override
68 public void visitToken(DetailAST ast) {
69 final String text = ast.getText();
70 if ((text.startsWith("0x") || text.startsWith("0X"))
71 && containsLowerLetter(text)) {
72 log(ast, MSG_KEY);
73 }
74 }
75
76 /**
77 * Checks if the given text contains any lowercase hexadecimal letter (a–f).
78 *
79 * @param text the literal text to check
80 * @return true if the literal contains lowercase hex digits; false otherwise
81 */
82 private static boolean containsLowerLetter(final String text) {
83 boolean result = false;
84 final char[] characterList = text.toCharArray();
85 for (char character : characterList) {
86 if (character >= A_ASCII && character <= F_ASCII) {
87 result = true;
88 break;
89 }
90 }
91 return result;
92 }
93
94 }