java - When the following Regex matches? -

i found following regex in 1 of android source file:

string regex = "\\s+(?i)src=\"cid(?-i):\\q" + attachment.mcontentid + "\\e\""; if(string.matches(regex)) {     print -- matched } else {     print -- not found } 

note: attachment.mcontentid have values c4ea83841e79f643970af3f20725cb04@gmail.com

i made sample code below:

string content = "hello src=\"cid:something@gmail.com\" present";     string contentid = "something@gmail.com";     string regex = "\\s+(?i)src=\"cid(?-i):\\q" + contentid + "\\e\"";     if(content.matches(regex))         system.out.println("present");     else         system.out.println("not present"); 

this gives "not present" output.

but when doing below:

system.out.println(content.replaceall(regex, " replaced value")); 

and output replaced new value. if not present, how replaceall work , replace new value? please clear confusions.

can kind of content in string make control go if part?

string regex = "\\s+(?i)src=\"cid(?-i):\\q" + attachment.mcontentid + "\\e\"";

break down:

\\s+ - match 1 or more spaces   (?i) - turn on case-insensitive matching subsequent string  src=\"cid - match src="cid  (?-i) - turn off case-insensitive matching  : - colon  \\q - treat following stuff before \\e literal characters,        , not control characters. special regex characters disabled until \\e  attachment.mcontentid - whatever string  \\e - end literal quoting sandwich started \\q  \" - end quote 

so match string src="cid:your-string-literal"

or, use own example, string match (there leading white space characters):

            src="cid:c4ea83841e79f643970af3f20725cb04@gmail.com" 

for update

the problem you're running using java.lang.string.matches() , expecting think should.

string.matches() (and matcher) has problem: tries match entire string against regular expression.

if use regex:

string regex = "\\s+(?i)src=\"cid(?-i):\\q" + attachment.mcontentid + "\\e\""; 

and input:

string content = "hello src=\"cid:something@gmail.com\" present"; 

content never match regex because entire string doesn't match regular expression.

what want use matcher.find - should work you.

string content = "hello src=\"cid:something@gmail.com\" present"; string contentid = "something@gmail.com"; pattern pattern = pattern.compile("\\s+(?i)src=\"cid(?-i):\\q" + contentid + "\\e\"");  matcher m = pattern.matcher(content);  if(m.find())     system.out.println("present"); else     system.out.println("not present"); 

ideone example: https://ideone.com/8rtf0e