001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 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_ASCII = 97;
048
049    /** ASCII value for lowercase 'f'. */
050    private static final int F_ASCII = 102;
051
052    @Override
053    public int[] getDefaultTokens() {
054        return getRequiredTokens();
055    }
056
057    @Override
058    public int[] getAcceptableTokens() {
059        return getRequiredTokens();
060    }
061
062    @Override
063    public int[] getRequiredTokens() {
064        return new int[] {TokenTypes.NUM_LONG, TokenTypes.NUM_INT};
065    }
066
067    @Override
068    public void visitToken(DetailAST ast) {
069        final String text = ast.getText();
070        if ((text.startsWith("0x") || text.startsWith("0X"))
071                && containsLowerLetter(text)) {
072            log(ast, MSG_KEY);
073        }
074    }
075
076    /**
077     * Checks if the given text contains any lowercase hexadecimal letter (a–f).
078     *
079     * @param text the literal text to check
080     * @return true if the literal contains lowercase hex digits; false otherwise
081     */
082    private static boolean containsLowerLetter(final String text) {
083        boolean result = false;
084        final char[] characterList = text.toCharArray();
085        for (char character : characterList) {
086            if (character >= A_ASCII && character <= F_ASCII) {
087                result = true;
088                break;
089            }
090        }
091        return result;
092    }
093
094}