Pattern compile(String regex, int flags) flags for what?-CodePudding

I am a little bit confused with this code below:

public class RegularEx {
    public static void main(String... arg) {
        Pattern pattern = Pattern.compile("M ", 5);
        Matcher matcher = pattern.matcher("M Merit Match MM m mM");
        while (matcher.find())
            System.out.print(matcher.group()   " ");
    }
}

in this part Pattern.compile("M ", 5);

According to https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#compile-java.lang.String-int- the number should represent flags that may include CASE_INSENSITIVE, MULTILINE, DOTALL, UNICODE_CASE, CANON_EQ, UNIX_LINES, LITERAL, UNICODE_CHARACTER_CLASS and COMMENTS

amount them , 5 should represent what?

Source: https://java.meritcampus.com/core-java-questions/Regular-Expression?t=195

CodePudding user response：

5 is a combination of 1 (UNIX_LINES) and 4 (COMMENTS), the full list of the constants can be found here.

java.util.regex.Pattern
Modifier and Type   Constant Field  Value
public static final int CANON_EQ    128
public static final int CASE_INSENSITIVE    2
public static final int COMMENTS    4
public static final int DOTALL  32
public static final int LITERAL 16
public static final int MULTILINE   8
public static final int UNICODE_CASE    64
public static final int UNICODE_CHARACTER_CLASS 256
public static final int UNIX_LINES  1

Never specify flags like that, instead do

Pattern pattern = Pattern.compile("M ", UNIX_LINES | COMMENTS);