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/*
 * Copyright (C) 2010 The Guava Authors
 *
 * Licensed 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 com.google.common.base;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;

/**
 * Static methods pertaining to ASCII characters (those in the range of values {@code 0x00} through
 * {@code 0x7F}), and to strings containing such characters.
 *
 * 

ASCII utilities also exist in other classes of this package: * *

    * *
  • {@link Charsets#US_ASCII} specifies the {@code Charset} of ASCII characters. *
  • {@link CharMatcher#ascii} matches ASCII characters and provides text processing methods * which operate only on the ASCII characters of a string. *
* * @author Catherine Berry * @author Gregory Kick * @since 7.0 */ @GwtCompatible public final class Ascii { private Ascii() {} /* The ASCII control characters, per RFC 20. */ /** * Null ('\0'): The all-zeros character which may serve to accomplish time fill and media fill. * Normally used as a C string terminator. * *

Although RFC 20 names this as "Null", note that it is distinct from the C/C++ "NULL" * pointer. * * @since 8.0 */ public static final byte NUL = 0; /** * Start of Heading: A communication control character used at the beginning of a sequence of * characters which constitute a machine-sensible address or routing information. Such a sequence * is referred to as the "heading." An STX character has the effect of terminating a heading. * * @since 8.0 */ public static final byte SOH = 1; /** * Start of Text: A communication control character which precedes a sequence of characters that * is to be treated as an entity and entirely transmitted through to the ultimate destination. * Such a sequence is referred to as "text." STX may be used to terminate a sequence of characters * started by SOH. * * @since 8.0 */ public static final byte STX = 2; /** * End of Text: A communication control character used to terminate a sequence of characters * started with STX and transmitted as an entity. * * @since 8.0 */ public static final byte ETX = 3; /** * End of Transmission: A communication control character used to indicate the conclusion of a * transmission, which may have contained one or more texts and any associated headings. * * @since 8.0 */ public static final byte EOT = 4; /** * Enquiry: A communication control character used in data communication systems as a request for * a response from a remote station. It may be used as a "Who Are You" (WRU) to obtain * identification, or may be used to obtain station status, or both. * * @since 8.0 */ public static final byte ENQ = 5; /** * Acknowledge: A communication control character transmitted by a receiver as an affirmative * response to a sender. * * @since 8.0 */ public static final byte ACK = 6; /** * Bell ('\a'): A character for use when there is a need to call for human attention. It may * control alarm or attention devices. * * @since 8.0 */ public static final byte BEL = 7; /** * Backspace ('\b'): A format effector which controls the movement of the printing position one * printing space backward on the same printing line. (Applicable also to display devices.) * * @since 8.0 */ public static final byte BS = 8; /** * Horizontal Tabulation ('\t'): A format effector which controls the movement of the printing * position to the next in a series of predetermined positions along the printing line. * (Applicable also to display devices and the skip function on punched cards.) * * @since 8.0 */ public static final byte HT = 9; /** * Line Feed ('\n'): A format effector which controls the movement of the printing position to the * next printing line. (Applicable also to display devices.) Where appropriate, this character may * have the meaning "New Line" (NL), a format effector which controls the movement of the printing * point to the first printing position on the next printing line. Use of this convention requires * agreement between sender and recipient of data. * * @since 8.0 */ public static final byte LF = 10; /** * Alternate name for {@link #LF}. ({@code LF} is preferred.) * * @since 8.0 */ public static final byte NL = 10; /** * Vertical Tabulation ('\v'): A format effector which controls the movement of the printing * position to the next in a series of predetermined printing lines. (Applicable also to display * devices.) * * @since 8.0 */ public static final byte VT = 11; /** * Form Feed ('\f'): A format effector which controls the movement of the printing position to the * first pre-determined printing line on the next form or page. (Applicable also to display * devices.) * * @since 8.0 */ public static final byte FF = 12; /** * Carriage Return ('\r'): A format effector which controls the movement of the printing position * to the first printing position on the same printing line. (Applicable also to display devices.) * * @since 8.0 */ public static final byte CR = 13; /** * Shift Out: A control character indicating that the code combinations which follow shall be * interpreted as outside of the character set of the standard code table until a Shift In * character is reached. * * @since 8.0 */ public static final byte SO = 14; /** * Shift In: A control character indicating that the code combinations which follow shall be * interpreted according to the standard code table. * * @since 8.0 */ public static final byte SI = 15; /** * Data Link Escape: A communication control character which will change the meaning of a limited * number of contiguously following characters. It is used exclusively to provide supplementary * controls in data communication networks. * * @since 8.0 */ public static final byte DLE = 16; /** * Device Control 1. Characters for the control of ancillary devices associated with data * processing or telecommunication systems, more especially switching devices "on" or "off." (If a * single "stop" control is required to interrupt or turn off ancillary devices, DC4 is the * preferred assignment.) * * @since 8.0 */ public static final byte DC1 = 17; // aka XON /** * Transmission On: Although originally defined as DC1, this ASCII control character is now better * known as the XON code used for software flow control in serial communications. The main use is * restarting the transmission after the communication has been stopped by the XOFF control code. * * @since 8.0 */ public static final byte XON = 17; // aka DC1 /** * Device Control 2. Characters for the control of ancillary devices associated with data * processing or telecommunication systems, more especially switching devices "on" or "off." (If a * single "stop" control is required to interrupt or turn off ancillary devices, DC4 is the * preferred assignment.) * * @since 8.0 */ public static final byte DC2 = 18; /** * Device Control 3. Characters for the control of ancillary devices associated with data * processing or telecommunication systems, more especially switching devices "on" or "off." (If a * single "stop" control is required to interrupt or turn off ancillary devices, DC4 is the * preferred assignment.) * * @since 8.0 */ public static final byte DC3 = 19; // aka XOFF /** * Transmission off. See {@link #XON} for explanation. * * @since 8.0 */ public static final byte XOFF = 19; // aka DC3 /** * Device Control 4. Characters for the control of ancillary devices associated with data * processing or telecommunication systems, more especially switching devices "on" or "off." (If a * single "stop" control is required to interrupt or turn off ancillary devices, DC4 is the * preferred assignment.) * * @since 8.0 */ public static final byte DC4 = 20; /** * Negative Acknowledge: A communication control character transmitted by a receiver as a negative * response to the sender. * * @since 8.0 */ public static final byte NAK = 21; /** * Synchronous Idle: A communication control character used by a synchronous transmission system * in the absence of any other character to provide a signal from which synchronism may be * achieved or retained. * * @since 8.0 */ public static final byte SYN = 22; /** * End of Transmission Block: A communication control character used to indicate the end of a * block of data for communication purposes. ETB is used for blocking data where the block * structure is not necessarily related to the processing format. * * @since 8.0 */ public static final byte ETB = 23; /** * Cancel: A control character used to indicate that the data with which it is sent is in error or * is to be disregarded. * * @since 8.0 */ public static final byte CAN = 24; /** * End of Medium: A control character associated with the sent data which may be used to identify * the physical end of the medium, or the end of the used, or wanted, portion of information * recorded on a medium. (The position of this character does not necessarily correspond to the * physical end of the medium.) * * @since 8.0 */ public static final byte EM = 25; /** * Substitute: A character that may be substituted for a character which is determined to be * invalid or in error. * * @since 8.0 */ public static final byte SUB = 26; /** * Escape: A control character intended to provide code extension (supplementary characters) in * general information interchange. The Escape character itself is a prefix affecting the * interpretation of a limited number of contiguously following characters. * * @since 8.0 */ public static final byte ESC = 27; /** * File Separator: These four information separators may be used within data in optional fashion, * except that their hierarchical relationship shall be: FS is the most inclusive, then GS, then * RS, and US is least inclusive. (The content and length of a File, Group, Record, or Unit are * not specified.) * * @since 8.0 */ public static final byte FS = 28; /** * Group Separator: These four information separators may be used within data in optional fashion, * except that their hierarchical relationship shall be: FS is the most inclusive, then GS, then * RS, and US is least inclusive. (The content and length of a File, Group, Record, or Unit are * not specified.) * * @since 8.0 */ public static final byte GS = 29; /** * Record Separator: These four information separators may be used within data in optional * fashion, except that their hierarchical relationship shall be: FS is the most inclusive, then * GS, then RS, and US is least inclusive. (The content and length of a File, Group, Record, or * Unit are not specified.) * * @since 8.0 */ public static final byte RS = 30; /** * Unit Separator: These four information separators may be used within data in optional fashion, * except that their hierarchical relationship shall be: FS is the most inclusive, then GS, then * RS, and US is least inclusive. (The content and length of a File, Group, Record, or Unit are * not specified.) * * @since 8.0 */ public static final byte US = 31; /** * Space: A normally non-printing graphic character used to separate words. It is also a format * effector which controls the movement of the printing position, one printing position forward. * (Applicable also to display devices.) * * @since 8.0 */ public static final byte SP = 32; /** * Alternate name for {@link #SP}. * * @since 8.0 */ public static final byte SPACE = 32; /** * Delete: This character is used primarily to "erase" or "obliterate" erroneous or unwanted * characters in perforated tape. * * @since 8.0 */ public static final byte DEL = 127; /** * The minimum value of an ASCII character. * * @since 9.0 (was type {@code int} before 12.0) */ public static final char MIN = 0; /** * The maximum value of an ASCII character. * * @since 9.0 (was type {@code int} before 12.0) */ public static final char MAX = 127; /** A bit mask which selects the bit encoding ASCII character case. */ private static final char CASE_MASK = 0x20; /** * Returns a copy of the input string in which all {@linkplain #isUpperCase(char) uppercase ASCII * characters} have been converted to lowercase. All other characters are copied without * modification. */ public static String toLowerCase(String string) { int length = string.length(); for (int i = 0; i < length; i++) { if (isUpperCase(string.charAt(i))) { char[] chars = string.toCharArray(); for (; i < length; i++) { char c = chars[i]; if (isUpperCase(c)) { chars[i] = (char) (c ^ CASE_MASK); } } return String.valueOf(chars); } } return string; } /** * Returns a copy of the input character sequence in which all {@linkplain #isUpperCase(char) * uppercase ASCII characters} have been converted to lowercase. All other characters are copied * without modification. * * @since 14.0 */ public static String toLowerCase(CharSequence chars) { if (chars instanceof String) { return toLowerCase((String) chars); } char[] newChars = new char[chars.length()]; for (int i = 0; i < newChars.length; i++) { newChars[i] = toLowerCase(chars.charAt(i)); } return String.valueOf(newChars); } /** * If the argument is an {@linkplain #isUpperCase(char) uppercase ASCII character} returns the * lowercase equivalent. Otherwise returns the argument. */ public static char toLowerCase(char c) { return isUpperCase(c) ? (char) (c ^ CASE_MASK) : c; } /** * Returns a copy of the input string in which all {@linkplain #isLowerCase(char) lowercase ASCII * characters} have been converted to uppercase. All other characters are copied without * modification. */ public static String toUpperCase(String string) { int length = string.length(); for (int i = 0; i < length; i++) { if (isLowerCase(string.charAt(i))) { char[] chars = string.toCharArray(); for (; i < length; i++) { char c = chars[i]; if (isLowerCase(c)) { chars[i] = (char) (c ^ CASE_MASK); } } return String.valueOf(chars); } } return string; } /** * Returns a copy of the input character sequence in which all {@linkplain #isLowerCase(char) * lowercase ASCII characters} have been converted to uppercase. All other characters are copied * without modification. * * @since 14.0 */ public static String toUpperCase(CharSequence chars) { if (chars instanceof String) { return toUpperCase((String) chars); } char[] newChars = new char[chars.length()]; for (int i = 0; i < newChars.length; i++) { newChars[i] = toUpperCase(chars.charAt(i)); } return String.valueOf(newChars); } /** * If the argument is a {@linkplain #isLowerCase(char) lowercase ASCII character} returns the * uppercase equivalent. Otherwise returns the argument. */ public static char toUpperCase(char c) { return isLowerCase(c) ? (char) (c ^ CASE_MASK) : c; } /** * Indicates whether {@code c} is one of the twenty-six lowercase ASCII alphabetic characters * between {@code 'a'} and {@code 'z'} inclusive. All others (including non-ASCII characters) * return {@code false}. */ public static boolean isLowerCase(char c) { // Note: This was benchmarked against the alternate expression "(char)(c - 'a') < 26" (Nov '13) // and found to perform at least as well, or better. return (c >= 'a') && (c <= 'z'); } /** * Indicates whether {@code c} is one of the twenty-six uppercase ASCII alphabetic characters * between {@code 'A'} and {@code 'Z'} inclusive. All others (including non-ASCII characters) * return {@code false}. */ public static boolean isUpperCase(char c) { return (c >= 'A') && (c <= 'Z'); } /** * Truncates the given character sequence to the given maximum length. If the length of the * sequence is greater than {@code maxLength}, the returned string will be exactly {@code * maxLength} chars in length and will end with the given {@code truncationIndicator}. Otherwise, * the sequence will be returned as a string with no changes to the content. * *

Examples: * *

{@code
   * Ascii.truncate("foobar", 7, "..."); // returns "foobar"
   * Ascii.truncate("foobar", 5, "..."); // returns "fo..."
   * }
* *

Note: This method may work with certain non-ASCII text but is not safe for use * with arbitrary Unicode text. It is mostly intended for use with text that is known to be safe * for use with it (such as all-ASCII text) and for simple debugging text. When using this method, * consider the following: * *

    *
  • it may split surrogate pairs *
  • it may split characters and combining characters *
  • it does not consider word boundaries *
  • if truncating for display to users, there are other considerations that must be taken * into account *
  • the appropriate truncation indicator may be locale-dependent *
  • it is safe to use non-ASCII characters in the truncation indicator *
* * * @throws IllegalArgumentException if {@code maxLength} is less than the length of {@code * truncationIndicator} * @since 16.0 */ public static String truncate(CharSequence seq, int maxLength, String truncationIndicator) { checkNotNull(seq); // length to truncate the sequence to, not including the truncation indicator int truncationLength = maxLength - truncationIndicator.length(); // in this worst case, this allows a maxLength equal to the length of the truncationIndicator, // meaning that a string will be truncated to just the truncation indicator itself checkArgument( truncationLength >= 0, "maxLength (%s) must be >= length of the truncation indicator (%s)", maxLength, truncationIndicator.length()); if (seq.length() <= maxLength) { String string = seq.toString(); if (string.length() <= maxLength) { return string; } // if the length of the toString() result was > maxLength for some reason, truncate that seq = string; } return new StringBuilder(maxLength) .append(seq, 0, truncationLength) .append(truncationIndicator) .toString(); } /** * Indicates whether the contents of the given character sequences {@code s1} and {@code s2} are * equal, ignoring the case of any ASCII alphabetic characters between {@code 'a'} and {@code 'z'} * or {@code 'A'} and {@code 'Z'} inclusive. * *

This method is significantly faster than {@link String#equalsIgnoreCase} and should be used * in preference if at least one of the parameters is known to contain only ASCII characters. * *

Note however that this method does not always behave identically to expressions such as: * *

    *
  • {@code string.toUpperCase().equals("UPPER CASE ASCII")} *
  • {@code string.toLowerCase().equals("lower case ascii")} *
* *

due to case-folding of some non-ASCII characters (which does not occur in {@link * String#equalsIgnoreCase}). However in almost all cases that ASCII strings are used, the author * probably wanted the behavior provided by this method rather than the subtle and sometimes * surprising behavior of {@code toUpperCase()} and {@code toLowerCase()}. * * @since 16.0 */ public static boolean equalsIgnoreCase(CharSequence s1, CharSequence s2) { // Calling length() is the null pointer check (so do it before we can exit early). int length = s1.length(); if (s1 == s2) { return true; } if (length != s2.length()) { return false; } for (int i = 0; i < length; i++) { char c1 = s1.charAt(i); char c2 = s2.charAt(i); if (c1 == c2) { continue; } int alphaIndex = getAlphaIndex(c1); // This was also benchmarked using '&' to avoid branching (but always evaluate the rhs), // however this showed no obvious improvement. if (alphaIndex < 26 && alphaIndex == getAlphaIndex(c2)) { continue; } return false; } return true; } /** * Returns the non-negative index value of the alpha character {@code c}, regardless of case. Ie, * 'a'/'A' returns 0 and 'z'/'Z' returns 25. Non-alpha characters return a value of 26 or greater. */ private static int getAlphaIndex(char c) { // Fold upper-case ASCII to lower-case and make zero-indexed and unsigned (by casting to char). return (char) ((c | CASE_MASK) - 'a'); } }





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