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.lang; /** * <p> * Operations on char primitives and Character objects. * </p> * * <p> * This class tries to handle <code>null</code> input gracefully. An exception * will not be thrown for a <code>null</code> input. Each method documents its * behaviour in more detail. * </p> * * <p> * #ThreadSafe# * </p> * * @author Apache Software Foundation * @since 2.1 * @version $Id: CharUtils.java 1056988 2011-01-09 17:58:53Z niallp $ */ public class CharUtils { private static final String CHAR_STRING = "\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007" + "\b\t\n\u000b\f\r\u000e\u000f" + "\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017" + "\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f" + "\u0020\u0021\"\u0023\u0024\u0025\u0026\u0027" + "\u0028\u0029\u002a\u002b\u002c\u002d\u002e\u002f" + "\u0030\u0031\u0032\u0033\u0034\u0035\u0036\u0037" + "\u0038\u0039\u003a\u003b\u003c\u003d\u003e\u003f" + "\u0040\u0041\u0042\u0043\u0044\u0045\u0046\u0047" + "\u0048\u0049\u004a\u004b\u004c\u004d\u004e\u004f" + "\u0050\u0051\u0052\u0053\u0054\u0055\u0056\u0057" + "\u0058\u0059\u005a\u005b\\\u005d\u005e\u005f" + "\u0060\u0061\u0062\u0063\u0064\u0065\u0066\u0067" + "\u0068\u0069\u006a\u006b\u006c\u006d\u006e\u006f" + "\u0070\u0071\u0072\u0073\u0074\u0075\u0076\u0077" + "\u0078\u0079\u007a\u007b\u007c\u007d\u007e\u007f"; private static final String[] CHAR_STRING_ARRAY = new String[128]; private static final Character[] CHAR_ARRAY = new Character[128]; /** * <code>\u000a</code> linefeed LF ('\n'). * * @see <a * href="http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#101089">JLF: * Escape Sequences for Character and String Literals</a> * @since 2.2 */ public static final char LF = '\n'; /** * <code>\u000d</code> carriage return CR ('\r'). * * @see <a * href="http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#101089">JLF: * Escape Sequences for Character and String Literals</a> * @since 2.2 */ public static final char CR = '\r'; static { for (int i = 127; i >= 0; i--) { CHAR_STRING_ARRAY[i] = CHAR_STRING.substring(i, i + 1); CHAR_ARRAY[i] = new Character((char) i); } } /** * <p> * <code>CharUtils</code> instances should NOT be constructed in standard * programming. Instead, the class should be used as * <code>CharUtils.toString('c');</code>. * </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> * * @param ch * the character to convert * @return a Character of the specified character */ public static Character toCharacterObject(char ch) { if (ch < CHAR_ARRAY.length) { return CHAR_ARRAY[ch]; } return new Character(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(String str) { if (StringUtils.isEmpty(str)) { return null; } return toCharacterObject(str.charAt(0)); } // ----------------------------------------------------------------------- /** * <p> * Converts the Character to a char throwing an exception for * <code>null</code>. * </p> * * <pre> * CharUtils.toChar(null) = IllegalArgumentException * CharUtils.toChar(' ') = ' ' * CharUtils.toChar('A') = 'A' * </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(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</code>. * </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(Character ch, 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(null) = IllegalArgumentException * CharUtils.toChar("") = IllegalArgumentException * CharUtils.toChar("A") = 'A' * CharUtils.toChar("BA") = 'B' * </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(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(String str, 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') = 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(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(char ch, 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(null) = IllegalArgumentException * CharUtils.toIntValue('3') = 3 * CharUtils.toIntValue('A') = 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(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(Character ch, 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(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</code> is passed in, <code>null</code> 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(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(char ch) { if (ch < 0x10) { return "\\u000" + Integer.toHexString(ch); } else if (ch < 0x100) { return "\\u00" + Integer.toHexString(ch); } else if (ch < 0x1000) { return "\\u0" + Integer.toHexString(ch); } return "\\u" + Integer.toHexString(ch); } /** * <p> * Converts the string to the unicode format '\u0020'. * </p> * * <p> * This format is the Java source code format. * </p> * * <p> * If <code>null</code> is passed in, <code>null</code> 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(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(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(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(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(char ch) { return (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z'); } /** * <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(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(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(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(char ch) { return (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z') || (ch >= '0' && ch <= '9'); } // ----------------- Following code copied from Apache Harmony (Character // class) /** * Indicates whether {@code ch} is a high- (or leading-) surrogate code unit * that is used for representing supplementary characters in UTF-16 * encoding. * * @param ch * the character to test. * @return {@code true} if {@code ch} is a high-surrogate code unit; * {@code false} otherwise. */ static boolean isHighSurrogate(char ch) { return ('\uD800' <= ch && '\uDBFF' >= ch); } }