ADDITIONAL SYSTEM INFORMATION :
Linux x64 based. tested with Java 11 and freshly downloaded jdk-18


A DESCRIPTION OF THE PROBLEM :
Regex Pattern.matches(REGEX, STRING) Failes to match \b boundry
Pattern.compile(REGEX).matcher(STRING) works as expected


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
just using \b at the end of a regex from Pattern.matches() function.

    if (Pattern.matches("HI\\b", "HI hi")) {
      System.out.println("I will not match properly");
    }
    if (Pattern.matches("HI\\b", "HI")) {
      System.out.println("I will match");
    }
    if (Pattern.compile("HI\\b").matcher("HI hi").find()) {
      System.out.println("I will match from compiled");
    }

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I will not match properly
I will match
I will match from compiled
ACTUAL -
I will match
I will match from compiled

---------- BEGIN SOURCE ----------
    if (Pattern.matches("HI\\b", "HI hi")) {
      System.out.println("I will not match properly");
    }
    if (Pattern.matches("HI\\b", "HI")) {
      System.out.println("I will match");
    }
    if (Pattern.compile("HI\\b").matcher("HI hi").find()) {
      System.out.println("I will match from compiled");
    }
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
use patther.compile pattern.

FREQUENCY : always