001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.checks;
021
022import com.puppycrawl.tools.checkstyle.StatelessCheck;
023import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
024import com.puppycrawl.tools.checkstyle.api.DetailAST;
025import com.puppycrawl.tools.checkstyle.api.TokenTypes;
026
027/**
028 * <div> Checks that hexadecimal literals are defined using uppercase letters {@code (A-F)}
029 * rather than lowercase {@code (a-f)}.
030 * This convention follows the
031 * <a href="https://cr.openjdk.org/~alundblad/styleguide/index-v6.html#toc-literals">
032 * OpenJDK Style Guide</a>.
033 * </div>
034 *
035 * @since 12.1.0
036 */
037@StatelessCheck
038public class HexLiteralCaseCheck extends AbstractCheck {
039
040    /**
041     * A key is pointing to the warning message text in "messages.properties"
042     * file.
043     */
044    public static final String MSG_KEY = "hex.literal";
045
046    /** ASCII value for lowercase 'a'. */
047    private static final int A_LOWER_ASCII = 97;
048
049    /** ASCII value for lowercase 'f'. */
050    private static final int F_LOWER_ASCII = 102;
051
052    /**
053     * Creates a new {@code HexLiteralCaseCheck} instance.
054     */
055    public HexLiteralCaseCheck() {
056        // no code by default
057    }
058
059    @Override
060    public int[] getDefaultTokens() {
061        return getRequiredTokens();
062    }
063
064    @Override
065    public int[] getAcceptableTokens() {
066        return getRequiredTokens();
067    }
068
069    @Override
070    public int[] getRequiredTokens() {
071        return new int[] {TokenTypes.NUM_LONG, TokenTypes.NUM_INT, TokenTypes.NUM_FLOAT,
072            TokenTypes.NUM_DOUBLE,
073        };
074    }
075
076    @Override
077    public void visitToken(DetailAST ast) {
078        final String text = ast.getText();
079        if (text.startsWith("0x") || text.startsWith("0X")) {
080            final int type = ast.getType();
081            if (type == TokenTypes.NUM_FLOAT || type == TokenTypes.NUM_DOUBLE) {
082                if (containsLowerLetterInHexFloatLiteral(text)) {
083                    log(ast, MSG_KEY);
084                }
085            }
086            else {
087                if (containsLowerLetter(text)) {
088                    log(ast, MSG_KEY);
089                }
090            }
091        }
092    }
093
094    /**
095     * Checks if the given text contains any lowercase hexadecimal letter (a–f).
096     *
097     * @param text the literal text to check
098     * @return true if the literal contains lowercase hex digits; false otherwise
099     */
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}