code: /*
   * 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>
   * 
   * @author Stephen Colebourne
   * @since 2.1
   * @version $Id: CharUtils.java 437554 2006-08-28 06:21:41Z bayard $
   */
  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('&copy;') = 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('&copy;') = 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('&copy;') = 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('&copy;') = 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('&copy;') = 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('&copy;') = 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('&copy;') = 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('&copy;') = 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');
      }
      
  }
  