如何在java中使用正则表达式来匹配单词

Question

I am trying to match a word (Source Ip) where each letter can be small or capital letter so i have wrote a regex pattern down but my m.find() is showing false even for Correct Match...

Is there any wrong in my regex pattern or the way I have written is wrong?

  String word = "Source Ip";
    String pattern = "[S|s][O|o][U|u][R|r][C|c][E|e]\\s*[I|i][P|p]";
    Pattern r = Pattern.compile(pattern);
    Matcher m = r.matcher(word);
    System.out.println(m.find());

Answer 1

You can simple use

String pattern = "SOURCE\\s*IP";
Pattern r = Pattern.compile(pattern, Pattern.CASE_INSENSITIVE);

Pattern.CASE_INSENSITIVE will make the matching case insensitive.

Answer 2

You don't need to alternate all letters between upper case and lowercase (note, as mentioned by others, the character class idiom does not require | to alternate - adding it between square brackets will also match the | literal).

You can parametrize your Pattern initialization with the Pattern.CASE_INSENSITIVE flag (alternative inline usage would be (?i) before your pattern representation).

For instance:

Pattern.compile("(?i)source\\s*ip");

... or ...

Pattern.compile("source\\s*ip", Pattern.CASE_INSENSITIVE);

Note

Flag API here .

Answer 3

This solution has the problem of accepting sourceip as well.

source\s*ip

Debuggex Demo

Therefore the correct answer should be

source\s+ip

Debuggex Demo

to force the presence of at least one whitespace between the two words.

To use this expression in Java you have to escape the backslash and use something like:

Pattern.compile("source\\s+ip", Pattern.CASE_INSENSITIVE);

Answer 4

if you really want to use regex though for some reason and not pattern. methods then this regex should suit your needs and it works just fine in java for me

 [s|S][o|O][U|u][r|R][c|C][e|E][ ]*[i|I][p|P]

your case of using

\\s*

won't identify spaces however this will

 \s*

you had one slash too many :)

EDIT: I demonstrate my ignorance, after checking regexpal I was wrong, [sS] is better than [s|S] [sS][oO][Uu][rR][cC][eE][ ]*[iI][pP] thank you Pshemo and yes i completely forgot about escaping characters Mena thank you for pointing that out for me