Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.lang3; /** * <p>Operations on char primitives and Character objects.</p> * * <p>This class tries to handle {@code null} input gracefully. * An exception will not be thrown for a {@code null} input. * Each method documents its behaviour in more detail.</p> * * <p>#ThreadSafe#</p> * @since 2.1 * @version $Id$ */ public class CharUtils { private static final String[] CHAR_STRING_ARRAY = new String[128]; private static final char[] HEX_DIGITS = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' }; /** * {@code \u000a} linefeed LF ('\n'). * * @see <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.10.6">JLF: Escape Sequences * for Character and String Literals</a> * @since 2.2 */ public static final char LF = '\n'; /** * {@code \u000d} carriage return CR ('\r'). * * @see <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.10.6">JLF: Escape Sequences * for Character and String Literals</a> * @since 2.2 */ public static final char CR = '\r'; static { for (char c = 0; c < CHAR_STRING_ARRAY.length; c++) { CHAR_STRING_ARRAY[c] = String.valueOf(c); } } /** * <p>{@code CharUtils} instances should NOT be constructed in standard programming. * Instead, the class should be used as {@code CharUtils.toString('c');}.</p> * * <p>This constructor is public to permit tools that require a JavaBean instance * to operate.</p> */ public CharUtils() { super(); } //----------------------------------------------------------------------- /** * <p>Converts the character to a Character.</p> * * <p>For ASCII 7 bit characters, this uses a cache that will return the * same Character object each time.</p> * * <pre> * CharUtils.toCharacterObject(' ') = ' ' * CharUtils.toCharacterObject('A') = 'A' * </pre> * * @deprecated Java 5 introduced {@link Character#valueOf(char)} which caches chars 0 through 127. * @param ch the character to convert * @return a Character of the specified character */ @Deprecated public static Character toCharacterObject(final char ch) { return Character.valueOf(ch); } /** * <p>Converts the String to a Character using the first character, returning * null for empty Strings.</p> * * <p>For ASCII 7 bit characters, this uses a cache that will return the * same Character object each time.</p> * * <pre> * CharUtils.toCharacterObject(null) = null * CharUtils.toCharacterObject("") = null * CharUtils.toCharacterObject("A") = 'A' * CharUtils.toCharacterObject("BA") = 'B' * </pre> * * @param str the character to convert * @return the Character value of the first letter of the String */ public static Character toCharacterObject(final String str) { if (StringUtils.isEmpty(str)) { return null; } return Character.valueOf(str.charAt(0)); } //----------------------------------------------------------------------- /** * <p>Converts the Character to a char throwing an exception for {@code null}.</p> * * <pre> * CharUtils.toChar(' ') = ' ' * CharUtils.toChar('A') = 'A' * CharUtils.toChar(null) throws IllegalArgumentException * </pre> * * @param ch the character to convert * @return the char value of the Character * @throws IllegalArgumentException if the Character is null */ public static char toChar(final Character ch) { if (ch == null) { throw new IllegalArgumentException("The Character must not be null"); } return ch.charValue(); } /** * <p>Converts the Character to a char handling {@code null}.</p> * * <pre> * CharUtils.toChar(null, 'X') = 'X' * CharUtils.toChar(' ', 'X') = ' ' * CharUtils.toChar('A', 'X') = 'A' * </pre> * * @param ch the character to convert * @param defaultValue the value to use if the Character is null * @return the char value of the Character or the default if null */ public static char toChar(final Character ch, final char defaultValue) { if (ch == null) { return defaultValue; } return ch.charValue(); } //----------------------------------------------------------------------- /** * <p>Converts the String to a char using the first character, throwing * an exception on empty Strings.</p> * * <pre> * CharUtils.toChar("A") = 'A' * CharUtils.toChar("BA") = 'B' * CharUtils.toChar(null) throws IllegalArgumentException * CharUtils.toChar("") throws IllegalArgumentException * </pre> * * @param str the character to convert * @return the char value of the first letter of the String * @throws IllegalArgumentException if the String is empty */ public static char toChar(final String str) { if (StringUtils.isEmpty(str)) { throw new IllegalArgumentException("The String must not be empty"); } return str.charAt(0); } /** * <p>Converts the String to a char using the first character, defaulting * the value on empty Strings.</p> * * <pre> * CharUtils.toChar(null, 'X') = 'X' * CharUtils.toChar("", 'X') = 'X' * CharUtils.toChar("A", 'X') = 'A' * CharUtils.toChar("BA", 'X') = 'B' * </pre> * * @param str the character to convert * @param defaultValue the value to use if the Character is null * @return the char value of the first letter of the String or the default if null */ public static char toChar(final String str, final char defaultValue) { if (StringUtils.isEmpty(str)) { return defaultValue; } return str.charAt(0); } //----------------------------------------------------------------------- /** * <p>Converts the character to the Integer it represents, throwing an * exception if the character is not numeric.</p> * * <p>This method coverts the char '1' to the int 1 and so on.</p> * * <pre> * CharUtils.toIntValue('3') = 3 * CharUtils.toIntValue('A') throws IllegalArgumentException * </pre> * * @param ch the character to convert * @return the int value of the character * @throws IllegalArgumentException if the character is not ASCII numeric */ public static int toIntValue(final char ch) { if (isAsciiNumeric(ch) == false) { throw new IllegalArgumentException("The character " + ch + " is not in the range '0' - '9'"); } return ch - 48; } /** * <p>Converts the character to the Integer it represents, throwing an * exception if the character is not numeric.</p> * * <p>This method coverts the char '1' to the int 1 and so on.</p> * * <pre> * CharUtils.toIntValue('3', -1) = 3 * CharUtils.toIntValue('A', -1) = -1 * </pre> * * @param ch the character to convert * @param defaultValue the default value to use if the character is not numeric * @return the int value of the character */ public static int toIntValue(final char ch, final int defaultValue) { if (isAsciiNumeric(ch) == false) { return defaultValue; } return ch - 48; } /** * <p>Converts the character to the Integer it represents, throwing an * exception if the character is not numeric.</p> * * <p>This method coverts the char '1' to the int 1 and so on.</p> * * <pre> * CharUtils.toIntValue('3') = 3 * CharUtils.toIntValue(null) throws IllegalArgumentException * CharUtils.toIntValue('A') throws IllegalArgumentException * </pre> * * @param ch the character to convert, not null * @return the int value of the character * @throws IllegalArgumentException if the Character is not ASCII numeric or is null */ public static int toIntValue(final Character ch) { if (ch == null) { throw new IllegalArgumentException("The character must not be null"); } return toIntValue(ch.charValue()); } /** * <p>Converts the character to the Integer it represents, throwing an * exception if the character is not numeric.</p> * * <p>This method coverts the char '1' to the int 1 and so on.</p> * * <pre> * CharUtils.toIntValue(null, -1) = -1 * CharUtils.toIntValue('3', -1) = 3 * CharUtils.toIntValue('A', -1) = -1 * </pre> * * @param ch the character to convert * @param defaultValue the default value to use if the character is not numeric * @return the int value of the character */ public static int toIntValue(final Character ch, final int defaultValue) { if (ch == null) { return defaultValue; } return toIntValue(ch.charValue(), defaultValue); } //----------------------------------------------------------------------- /** * <p>Converts the character to a String that contains the one character.</p> * * <p>For ASCII 7 bit characters, this uses a cache that will return the * same String object each time.</p> * * <pre> * CharUtils.toString(' ') = " " * CharUtils.toString('A') = "A" * </pre> * * @param ch the character to convert * @return a String containing the one specified character */ public static String toString(final char ch) { if (ch < 128) { return CHAR_STRING_ARRAY[ch]; } return new String(new char[] { ch }); } /** * <p>Converts the character to a String that contains the one character.</p> * * <p>For ASCII 7 bit characters, this uses a cache that will return the * same String object each time.</p> * * <p>If {@code null} is passed in, {@code null} will be returned.</p> * * <pre> * CharUtils.toString(null) = null * CharUtils.toString(' ') = " " * CharUtils.toString('A') = "A" * </pre> * * @param ch the character to convert * @return a String containing the one specified character */ public static String toString(final Character ch) { if (ch == null) { return null; } return toString(ch.charValue()); } //-------------------------------------------------------------------------- /** * <p>Converts the string to the Unicode format '\u0020'.</p> * * <p>This format is the Java source code format.</p> * * <pre> * CharUtils.unicodeEscaped(' ') = "\u0020" * CharUtils.unicodeEscaped('A') = "\u0041" * </pre> * * @param ch the character to convert * @return the escaped Unicode string */ public static String unicodeEscaped(final char ch) { StringBuilder sb = new StringBuilder(6); sb.append("\\u"); sb.append(HEX_DIGITS[(ch >> 12) & 15]); sb.append(HEX_DIGITS[(ch >> 8) & 15]); sb.append(HEX_DIGITS[(ch >> 4) & 15]); sb.append(HEX_DIGITS[(ch) & 15]); return sb.toString(); } /** * <p>Converts the string to the Unicode format '\u0020'.</p> * * <p>This format is the Java source code format.</p> * * <p>If {@code null} is passed in, {@code null} will be returned.</p> * * <pre> * CharUtils.unicodeEscaped(null) = null * CharUtils.unicodeEscaped(' ') = "\u0020" * CharUtils.unicodeEscaped('A') = "\u0041" * </pre> * * @param ch the character to convert, may be null * @return the escaped Unicode string, null if null input */ public static String unicodeEscaped(final Character ch) { if (ch == null) { return null; } return unicodeEscaped(ch.charValue()); } //-------------------------------------------------------------------------- /** * <p>Checks whether the character is ASCII 7 bit.</p> * * <pre> * CharUtils.isAscii('a') = true * CharUtils.isAscii('A') = true * CharUtils.isAscii('3') = true * CharUtils.isAscii('-') = true * CharUtils.isAscii('\n') = true * CharUtils.isAscii('©') = false * </pre> * * @param ch the character to check * @return true if less than 128 */ public static boolean isAscii(final char ch) { return ch < 128; } /** * <p>Checks whether the character is ASCII 7 bit printable.</p> * * <pre> * CharUtils.isAsciiPrintable('a') = true * CharUtils.isAsciiPrintable('A') = true * CharUtils.isAsciiPrintable('3') = true * CharUtils.isAsciiPrintable('-') = true * CharUtils.isAsciiPrintable('\n') = false * CharUtils.isAsciiPrintable('©') = false * </pre> * * @param ch the character to check * @return true if between 32 and 126 inclusive */ public static boolean isAsciiPrintable(final char ch) { return ch >= 32 && ch < 127; } /** * <p>Checks whether the character is ASCII 7 bit control.</p> * * <pre> * CharUtils.isAsciiControl('a') = false * CharUtils.isAsciiControl('A') = false * CharUtils.isAsciiControl('3') = false * CharUtils.isAsciiControl('-') = false * CharUtils.isAsciiControl('\n') = true * CharUtils.isAsciiControl('©') = false * </pre> * * @param ch the character to check * @return true if less than 32 or equals 127 */ public static boolean isAsciiControl(final char ch) { return ch < 32 || ch == 127; } /** * <p>Checks whether the character is ASCII 7 bit alphabetic.</p> * * <pre> * CharUtils.isAsciiAlpha('a') = true * CharUtils.isAsciiAlpha('A') = true * CharUtils.isAsciiAlpha('3') = false * CharUtils.isAsciiAlpha('-') = false * CharUtils.isAsciiAlpha('\n') = false * CharUtils.isAsciiAlpha('©') = false * </pre> * * @param ch the character to check * @return true if between 65 and 90 or 97 and 122 inclusive */ public static boolean isAsciiAlpha(final char ch) { return isAsciiAlphaUpper(ch) || isAsciiAlphaLower(ch); } /** * <p>Checks whether the character is ASCII 7 bit alphabetic upper case.</p> * * <pre> * CharUtils.isAsciiAlphaUpper('a') = false * CharUtils.isAsciiAlphaUpper('A') = true * CharUtils.isAsciiAlphaUpper('3') = false * CharUtils.isAsciiAlphaUpper('-') = false * CharUtils.isAsciiAlphaUpper('\n') = false * CharUtils.isAsciiAlphaUpper('©') = false * </pre> * * @param ch the character to check * @return true if between 65 and 90 inclusive */ public static boolean isAsciiAlphaUpper(final char ch) { return ch >= 'A' && ch <= 'Z'; } /** * <p>Checks whether the character is ASCII 7 bit alphabetic lower case.</p> * * <pre> * CharUtils.isAsciiAlphaLower('a') = true * CharUtils.isAsciiAlphaLower('A') = false * CharUtils.isAsciiAlphaLower('3') = false * CharUtils.isAsciiAlphaLower('-') = false * CharUtils.isAsciiAlphaLower('\n') = false * CharUtils.isAsciiAlphaLower('©') = false * </pre> * * @param ch the character to check * @return true if between 97 and 122 inclusive */ public static boolean isAsciiAlphaLower(final char ch) { return ch >= 'a' && ch <= 'z'; } /** * <p>Checks whether the character is ASCII 7 bit numeric.</p> * * <pre> * CharUtils.isAsciiNumeric('a') = false * CharUtils.isAsciiNumeric('A') = false * CharUtils.isAsciiNumeric('3') = true * CharUtils.isAsciiNumeric('-') = false * CharUtils.isAsciiNumeric('\n') = false * CharUtils.isAsciiNumeric('©') = false * </pre> * * @param ch the character to check * @return true if between 48 and 57 inclusive */ public static boolean isAsciiNumeric(final char ch) { return ch >= '0' && ch <= '9'; } /** * <p>Checks whether the character is ASCII 7 bit numeric.</p> * * <pre> * CharUtils.isAsciiAlphanumeric('a') = true * CharUtils.isAsciiAlphanumeric('A') = true * CharUtils.isAsciiAlphanumeric('3') = true * CharUtils.isAsciiAlphanumeric('-') = false * CharUtils.isAsciiAlphanumeric('\n') = false * CharUtils.isAsciiAlphanumeric('©') = false * </pre> * * @param ch the character to check * @return true if between 48 and 57 or 65 and 90 or 97 and 122 inclusive */ public static boolean isAsciiAlphanumeric(final char ch) { return isAsciiAlpha(ch) || isAsciiNumeric(ch); } /** * <p>Compares two {@code char} values numerically. This is the same functionality as provided in Java 7.</p> * * @param x the first {@code char} to compare * @param y the second {@code char} to compare * @return the value {@code 0} if {@code x == y}; * a value less than {@code 0} if {@code x < y}; and * a value greater than {@code 0} if {@code x > y} * @since 3.4 */ public static int compare(char x, char y) { return x - y; } }