匹配java中的String正则表达式？

Question

I have below lines of java code.

            String string1 = "SAMPLE STRING";
            String string2 = "SAMPLE*";

            string2 = string2.replaceAll("\\*",".*").trim().toUpperCase();

            if(string1.matches(string2)){
                System.out.println("true");
            }else{
                System.out.println("false");
            }

Here i dont understand the regex meaning here. what does it mean? Can anyone please help me?

Thanks!

Answer 1

So your regex here is "\\\\*" which simply means character * . The replaceAll() here will replace all * characters in string2 with .* .

This is a common replace to have people use simplified regexes (like the ones used to match files, eg *.exe ) and convert it to a PCRE regex , which is the regex used in Java.

Answer 2

Regex "\\*" simply means ' ', when applied on string2 = SAMPLE by replaceAll() the string2 became SAMPLE.* and this is again a regex used by Matcher for match().

"SAMPLE.*" simply accepts everything followed by "SAMPLE"

Hence, "SAMPLE STRING" matched "SAMPLE.*".

Similarly, "SAMPLE ", "SAMPLE 123SSS", "SAMPLE" etc. will match. But, " SAMPLE STRING" doesn't matches pattern "SAMPLE.*"