Pattern compile(String,int) method in Java with Examples

The compile(String, int) method of the Pattern class used to create a pattern from the regular expression with the help of flags where both expression and flags are passed as parameters to the method. The Pattern class contains a list of flags (int constants) that can be helpful to make the Pattern matching behave in certain ways. For example, The flag name CASE_INSENSITIVE is used to ignore the case of the text at the time of matching.
Syntax:

public static Pattern compile(String regex, int flags)

Parameters: This method accepts two parameters:

regex: This parameter represents the given regular expression compiled into a pattern.
flag: This parameter is an integer representing Match flags, a bit mask that may include CASE_INSENSITIVE, MULTILINE, DOTALL, UNICODE_CASE, CANON_EQ, UNIX_LINES, LITERAL, UNICODE_CHARACTER_CLASS and COMMENTS.

Return Value: This method returns the pattern compiled from passed regex and flags.
Exception: This method throws following exceptions:

PatternSyntaxException: This exception is raised if the expression’s syntax is invalid.
IllegalArgumentException: This exception is raised if bit values other than those corresponding to the defined match flags are set in flags.

Below programs illustrate the compile(String, int) method:
Program 1:

Java

// Java program to demonstrate
// Pattern.compile method
 
import java.util.regex.*;
 
public class GFG {

    public static void main(String[] args)

    {

        // create a REGEX String

        String REGEX = "(.*)(for)(.*)?";
 
        // create the string

        // in which you want to search

        String actualString

            = "code of Machine";
 
        // compile the regex to create pattern

        // using compile() method

        Pattern pattern = Pattern.compile(REGEX, 

                           Pattern.CASE_INSENSITIVE);
 
        // check whether Regex string is

        // found in actualString or not

        boolean matches = pattern

                              .matcher(actualString)

                              .matches();
 
        System.out.println("actualString "

                           + "contains REGEX = "

                           + matches);

    }
}

Output:

actualString contains REGEX = false

Time Complexity : O(N)

Space Complexity : O(1)

Program 2:

Java

// Java program to demonstrate
// Pattern.compile method
 
import java.util.regex.*;
 
public class GFG {

    public static void main(String[] args)

    {

        // create a REGEX String

        String REGEX = ".*org.*";
 
        // create the string

        // in which you want to search

        String actualString

            = "geeksforgeeks.org";
 
        // compile the regex to create pattern

        // using compile() method

        Pattern pattern = Pattern.compile(REGEX, 

                             Pattern.CASE_INSENSITIVE);
 
        // check whether Regex string is

        // found in actualString or not

        boolean matches = pattern

                              .matcher(actualString)

                              .matches();
 
        System.out.println("actualString "

                           + "contains REGEX = "

                           + matches);

    }
}