在Java中使用String.matches（）

Question

Let's see the following expressions about String.matches() in Java.

System.out.println("55CCEE".matches("[0-9A-Za-z]{6}"));  //true
System.out.println("CC77HH".matches("[0-9A-Za-z]{6}"));  //true
System.out.println("CC1156".matches("[0-9A-Za-z]{6}"));  //true

System.out.println("С".matches("[0-9A-Za-z]{1}"));       //false
System.out.println("СС".matches("[0-9A-Za-z]{2}"));      //false
System.out.println("СС5588".matches("[0-9A-Za-z]{6}"));  //false
System.out.println("СС5589".matches("[0-9A-Za-z]{6}"));  //false

The first three cases look fine and work as expected. The rest of the cases, however seem to be failing and return false which wasn't expected. Why does this happen?

Answer 1

In the second set, you don't have a C in your string, you have a С which is 0xd0 0xa1 in UTF-8.

That char is Cyrillic - CYRILLIC CAPITAL LETTER ES . See the Cyrillic code chart (PDF) at unicode.org.

Answer 2

The 'C' character in the lines that are failing is a different Unicode character than the C in the [AZ] character class.

    int unicodeFrom3rdLine = 'C';
    int unicodeFrom4thLine = 'С';
    System.out.println(Integer.toHexString(unicodeFrom3rdLine));
    System.out.println(Integer.toHexString(unicodeFrom4thLine));

produces

    43
    421

Even though they look the same, they're actually different characters, the former being the normal C and latter being Cyrillic .