The pattern class of java.regex package is a compiled representation of a regular expression.
The compile() method of this class accepts a string value representing a regular expression and returns a Pattern object, the following is the signature of this method.
static Pattern compile(String regex)
Another variant of this method accepts an integer value representing flags, following is the signature of the compile method with two parameters.
static Pattern compile(String regex, int flags)
The Pattern class provides various fields each representing a flag
| S.No | Field and Description |
|---|---|
| 1 | CANON_EQ Matches two characters only if they are canonically equal. |
| 2 | CASE_INSENSITIVE Matches characters irrespective of case. |
| 3 | COMMENTS Allows whitespace and comments in pattern. |
| 4 | DOTALL Enables dotall mode. Where the “.” Meta character matches all the characters including line terminators. |
| 5 | LITERAL Enables literal parsing of the pattern. i.e. all the metacharacters and escape sequences in the input sequence are treated as literal characters. |
| 6 | MULTILINE Enables multiline mode i.e. the whole input sequence is treated as a single line. |
| 7 | UNICODE_CASE Enables Unicode-aware case folding i.e. when used along with CASE_INSENSITIVE. if you search for Unicode characters using regular expressions Unicode characters of both cases will be matched. |
| 8 | UNICODE_CHARACTER_CLASS Enables the Unicode version of Predefined character classes and POSIX character classes. |
| 9 | UNIX_LINES This flag enables Unix lines mode. |
The flags() method of this class returns the flag used in the current pattern.
Example
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class COMMENTES_Example {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter your name: ");
String name = sc.nextLine();
System.out.println("Enter your Date of birth: ");
String dob = sc.nextLine();
//Regular expression to accept date in MM-DD-YYY format
String regex = "^(1[0-2]|0[1-9])/ # For Month\n" + "(3[01]|[12][0-9]|0[1-9])/ # For Date\n"
+ "[0-9]{4}$ # For Year";
//Creating a Pattern object
Pattern pattern = Pattern.compile(regex, Pattern.COMMENTS);
//Creating a Matcher object
Matcher matcher = pattern.matcher(dob);
boolean result = matcher.matches();
if(result) {
System.out.println("Given date of birth is valid");
} else {
System.out.println("Given date of birth is not valid");
}
System.out.println("Flag used: "+ pattern.flags());
}
}Output
Enter your name: Krishna Enter your Date of birth: 09/26/1989 Given date of birth is valid Flag used: 4