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:Â Â
public static Pattern compile(String regex, int flags)
Parameters: This method accepts two parameters:Â Â
- 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:Â Â
- 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:Â
Java
// Java program to demonstrate// Pattern.compile methodÂ
import java.util.regex.*;Â
public class GFG {    public static void main(String[] args)    {        // create a REGEX String        String REGEX = "(.*)(for)(.*)?";Â
        // create the string        // in which you want to search        String actualString            = "code of Machine";Â
        // compile the regex to create pattern        // using compile() method        Pattern pattern = Pattern.compile(REGEX,                           Pattern.CASE_INSENSITIVE);Â
        // check whether Regex string is        // found in actualString or not        boolean matches = pattern                              .matcher(actualString)                              .matches();Â
        System.out.println("actualString "                           + "contains REGEX = "                           + matches);    }} |
actualString contains REGEX = false
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Time Complexity : O(N)
Space Complexity : O(1)
Program 2:Â
Â
Java
// Java program to demonstrate// Pattern.compile methodÂ
import java.util.regex.*;Â
public class GFG {    public static void main(String[] args)    {        // create a REGEX String        String REGEX = ".*org.*";Â
        // create the string        // in which you want to search        String actualString            = "geeksforgeeks.org";Â
        // compile the regex to create pattern        // using compile() method        Pattern pattern = Pattern.compile(REGEX,                             Pattern.CASE_INSENSITIVE);Â
        // check whether Regex string is        // found in actualString or not        boolean matches = pattern                              .matcher(actualString)                              .matches();Â
        System.out.println("actualString "                           + "contains REGEX = "                           + matches);    }} |
actualString contains REGEX = true
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Time Complexity : O(N)
Space Complexity : O(1)
References:Â
https://docs.oracle.com/javase/10/docs/api/java/util/regex/Pattern.html#compile(java.lang.String, int)
