An issue with matching a simple regex in Java [duplicate]

Question

I have a problem matching regex in Java, my text is:

Temperature: 9°C (48°F), Wind Direction: South South Westerly, Wind Speed: 19mph, Humidity: 87%, Pressure: 1018mb, Rising, Visibility: Good

My regex is

\bTemperature:[^,]*

The matching code:

import java.util.regex.Matcher;
import java.util.regex.Pattern;
class Main {
  public static void main(String[] args) {
    Pattern p = Pattern.compile("\bTemperature:[^,]*");

    Matcher m = p.matcher("Temperature: 10°C (50°F), Wind Direction: South South Easterly, Wind Speed: 25mph, Humidity: 78%, Pressure: 1014mb, Falling, Visibility: Good");

    if(m.find())
    {
      System.out.println(m.group());
    }

  }
}

It does not output anything.

xingbin · Accepted Answer · 2018-03-03 16:52:54Z

4

Try use Pattern p = Pattern.compile("\\bTemperature:[^,]*"); to escape.

As user John Bollinger said in the comment:

You need a backslash to be read and interpreted by the Pattern class, but backslashes in string literals are subject to interpretation by the Java compiler. The compiler converts a doubled backslash to a single backslash, just as Pattern requires.

The two backslashes will be compiled as one.

So when you reading the regex pattern string from file or console, you just need one backslash.

edited Mar 3, 2018 at 16:52

answered Mar 3, 2018 at 15:03

xingbin

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1 Comment

John Bollinger Over a year ago

To clarify: you need a backslash to be read and interpreted by the Pattern class, but backslashes in string literals are subject to interpretation by the Java compiler. The compiler converts a doubled backslash to a single backslash, just as Pattern requires.

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