regular expression in java

[Chen Yang]

Hi,

In String class, we can use

boolean matches(String regex)

to deal with string data. But when I write:

String da = new String("function");
System.out.print(da.matches("\bfunction\b"));

And it returns false.

I think \b means a word boundary. So it should return true in this case. I
can't figure out why, plez help me, thanks in advance.

 

[VisionSet]

Hi,

In String class, we can use

boolean matches(String regex)

to deal with string data. But when I write:

String da = new String("function");
System.out.print(da.matches("\bfunction\b"));

And it returns false.

I think \b means a word boundary. So it should return true in this case. I
can't figure out why, plez help me, thanks in advance.

try:

String da = new String("function");
System.out.print(da.matches("\\bfunction\\b"));


the 1st \ escapes so the 2nd can be passed to the regex engine

 

[Chen Yang]

Thanks a lot in the first place. It does work. But when I use

String da = new String("this is a function");
System.out.print(da.matches("\\bfunction\\b"));

It returns false again.

I am wondering how to implement it as in regular expression... I found an
article from google, and it says " It is important to remember that
String.matches() only returns true if the entire string can be matched." So
does it mean we can't use /\bblahblah\b/ as we use in awk or something like
that? Thanks again for your reply.

http://www.regular-expressions.info/java.html

Chen

 

[VisionSet]

Thanks a lot in the first place. It does work. But when I use

String da = new String("this is a function");
System.out.print(da.matches("\\bfunction\\b"));

It returns false again.

I am wondering how to implement it as in regular expression... I found an
article from google, and it says " It is important to remember that
String.matches() only returns true if the entire string can be matched." So
does it mean we can't use /\bblahblah\b/ as we use in awk or something like
that? Thanks again for your reply.

Because that method matches the *entire* input against the regex. There are
other methods that search for a match. But that one can be forced to work
by putting int .* at either end ie accept anything before & after. ie

String da = new String("this is a function");
System.out.print(da.matches(".*\\bfunction\\b.*"));

look at java.util.regex.Matcher.find() for searching within strings

 

[Chen Yang]

Hi,

Thanks a lot! I totally understand now. So it means I can only use this
regular expression to compare with "the whole" string. Thanks again.

Chen

 

[Roedy Green]

String da = new String("function");
System.out.print(da.matches("\bfunction\b"));

And it returns false.

I think \b means a word boundary. So it should return true in this case. I

I would write that as:

String da = "function";

Matcher m = pattern.matcher( da );

System.out.println( m.matches() );

....

static Pattern pattern = Pattern.compile( "\\sfunction\\s" );

 

[Roedy Green]

Thanks a lot! I totally understand now. So it means I can only use this
regular expression to compare with "the whole" string. Thanks again.

you were confusing matching with finding.
See http://mindprod.com/jgloss/regex.html