Usage in Java Pattern.compile function

Addition of Pattern.compile the Pattern (String REGEX),
the Pattern class compile () There is another version:
the Pattern Pattern.complie (String REGEX, int In Flag) , which accepts a parameter marker flag, to adjust the matching behavior.
Pattern flag from the following class constants:

Compiler flags	effect
Pattern.CANON_EQ	Two characters if and only if they are completely decomposed to match the specification, they are considered a match, for example, if we specify this flag, the expression a \ u030A will match the string? . By default, the standard does not consider matching equivalence
Pattern.CASE_INSENSITIVE(?i)	By default, case-insensitive matching assumes that only US-ASCII character set can take place. This tag allows pattern matching without considering the case (upper or lower case). By specifying UNICODE_CASE marks and combine this tag, case-insensitive Unicode-based matching can open, you can also use the embedded tag expression? I open, the same below
Pattern.COMMENTS(?x)	In this mode, the expression of space ( not referring to \ S , merely referring to spaces) will be ignored, and beginning with # comment until the end of the line will be ignored. Expressions by embedding tag line mode can also be turned in Unix
Pattern.DOTALL(?s)	In dotall mode, the expression. "" Matches all characters, including the line terminator. By default, "." Expression does not match line terminators
Pattern.MULTLINE(?m)	In the multi-line mode, and expression ^ $ matching row or respectively the beginning and ending of the string. By default, these expressions to match only the beginning of a string of input and complete end
Pattern.UNICODE_CASE(?u)	When specifying the tag, and opens CASE_INSENSITIVE , the case-insensitive match will manner consistent with the Unicode standard. By default, case-insensitive matching assumes that only the US-ASCII character set to
Pattern.UNIX_LINES(?d)	In this mode,., ^ $ Behavior and recognizes only the line terminator \ n

In these tags Pattern.CASE_INSENSITIVE(?i) ，Pattern.MULTLINE(?m), == Pattern.COMMENTS (? X) == particularly useful.

Use example:
we can "or" | functional operation of combining a plurality of markers ()

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class ReFlags {

	public static void main(String[] args) {
		
		Pattern p=Pattern.compile("^java",Pattern.CASE_INSENSITIVE|Pattern.MULTILINE);
		/*
		 * 使用Pattern.CASE_INSENSITIVE（大小写不敏感的匹配）和Pattern.MULTILINE（多行模式）标记，忽略大小写地匹配所有以java开头的行
		 */
		
		Matcher m=p.matcher("java has regex\nJava has regex\n"
				+ "JAVA has pretty good regular expression\n"
				+ "Regular expressions are in JavA");
		while (m.find()) {	
			System.out.println(m.group());//输出已匹配的部分		
		}
	}

}

Output:

java
Java
JAVA

Use Pattern.COMMENTS (? X) examples:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class ReFlags_Comments {

	public static void main(String[] args) {
		/*
		 * 不使用Pattern.COMMENTS(不启动注释)
		 */
         String s="123";
         Pattern p1=Pattern.compile(" (\\d+)+#test comments");
         Matcher m1=p1.matcher(s);
         System.out.println(m1.matches());//false
         /*
                    * 正则表达式中使用启动注释的标记
          */
         Pattern p2=Pattern.compile("(?x) (\\d+)+#test comments");
         Matcher m2=p2.matcher(s);
         System.out.println(m2.matches());//true
         /*
               * 参数中使用Pattern.COMMENTS以启动注释
          */
         Pattern p3=Pattern.compile("  (\\d+)+#test comments",Pattern.COMMENTS);
         Matcher m3=p3.matcher(s);
         System.out.println(m3.matches());//true	
	}

}

operation result:

false
true
true

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Reference books: "Thinking in Java"