In Java, is it possible to check if a String is only ASCII?

Question

Character.isLetter(c) returns true if the character is a letter. But is there a way to quickly find if a String only contains the base characters of ASCII?

Answer 1

Iterate through the string, and use charAt() to get the char. Then treat it as an int, and see if it has a unicode value (a superset of ASCII) which you like.

Break at the first you don't like.

Answer 2

Using Guava you could just write:

boolean isAscii = CharMatcher.ASCII.matchesAllOf(someString);

Answer 3

You can do it with java.nio.charset.Charset.

import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;

public class StringUtils {

  static CharsetEncoder asciiEncoder = 
      Charset.forName("US-ASCII").newEncoder(); // or "ISO-8859-1" for ISO Latin 1

  public static boolean isPureAscii(String v) {
    return asciiEncoder.canEncode(v);
  }

  public static void main (String args[])
    throws Exception {

     String test = "Réal";
     System.out.println(test + " isPureAscii() : " + StringUtils.isPureAscii(test));
     test = "Real";
     System.out.println(test + " isPureAscii() : " + StringUtils.isPureAscii(test));

     /*
      * output :
      *   Réal isPureAscii() : false
      *   Real isPureAscii() : true
      */
  }
}

Detect non-ASCII character in a String

Answer 4

Here is another way not depending on a library but using a regex.

You can use this single line:

text.matches("\\A\\p{ASCII}*\\z")

Whole example program:

public class Main {
    public static void main(String[] args) {
        char nonAscii = 0x00FF;
        String asciiText = "Hello";
        String nonAsciiText = "Buy: " + nonAscii;
        System.out.println(asciiText.matches("\\A\\p{ASCII}*\\z"));
        System.out.println(nonAsciiText.matches("\\A\\p{ASCII}*\\z"));
    }
}

Answer 5

Iterate through the string and make sure all the characters have a value less than 128.

Java Strings are conceptually encoded as UTF-16. In UTF-16, the ASCII character set is encoded as the values 0 - 127 and the encoding for any non ASCII character (which may consist of more than one Java char) is guaranteed not to include the numbers 0 - 127