1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2026 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_LOWER_ASCII = 97;
48
49 /** ASCII value for lowercase 'f'. */
50 private static final int F_LOWER_ASCII = 102;
51
52 /**
53 * Creates a new {@code HexLiteralCaseCheck} instance.
54 */
55 public HexLiteralCaseCheck() {
56 // no code by default
57 }
58
59 @Override
60 public int[] getDefaultTokens() {
61 return getRequiredTokens();
62 }
63
64 @Override
65 public int[] getAcceptableTokens() {
66 return getRequiredTokens();
67 }
68
69 @Override
70 public int[] getRequiredTokens() {
71 return new int[] {TokenTypes.NUM_LONG, TokenTypes.NUM_INT, TokenTypes.NUM_FLOAT,
72 TokenTypes.NUM_DOUBLE,
73 };
74 }
75
76 @Override
77 public void visitToken(DetailAST ast) {
78 final String text = ast.getText();
79 if (text.startsWith("0x") || text.startsWith("0X")) {
80 final int type = ast.getType();
81 if (type == TokenTypes.NUM_FLOAT || type == TokenTypes.NUM_DOUBLE) {
82 if (containsLowerLetterInHexFloatLiteral(text)) {
83 log(ast, MSG_KEY);
84 }
85 }
86 else {
87 if (containsLowerLetter(text)) {
88 log(ast, MSG_KEY);
89 }
90 }
91 }
92 }
93
94 /**
95 * Checks if the given text contains any lowercase hexadecimal letter (a–f).
96 *
97 * @param text the literal text to check
98 * @return true if the literal contains lowercase hex digits; false otherwise
99 */
100 private static boolean containsLowerLetter(final String text) {
101 boolean result = false;
102 final char[] characterList = text.toCharArray();
103 for (char character : characterList) {
104 if (character >= A_LOWER_ASCII && character <= F_LOWER_ASCII) {
105 result = true;
106 break;
107 }
108 }
109 return result;
110 }
111
112 /**
113 * Checks if the given text contains any lowercase hexadecimal letter in
114 * Hex Float Literal (a–f).
115 *
116 * @param text the literal text to check
117 * @return true if the literal contains lowercase hex digits; false otherwise
118 */
119 public static boolean containsLowerLetterInHexFloatLiteral(final String text) {
120 boolean result = false;
121
122 final int index = text.length() - 1;
123 for (char character : text.substring(0, index).toCharArray()) {
124 if (character >= A_LOWER_ASCII && character <= F_LOWER_ASCII) {
125 result = true;
126 break;
127 }
128 }
129
130 return result;
131 }
132
133 }