Java Pattern Matcher: create new or reset?

Question

Assume a Regular Expression, which, via a Java Matcher object, is matched against a large number of strings:

String expression = ...; // The Regular Expression Pattern pattern = Pattern.compile(expression); String[] ALL_INPUT = ...; // The large number of strings to be matched  Matcher matcher; // Declare but not initialize a Matcher  for (String input:ALL_INPUT) {     matcher = pattern.matcher(input); // Create a new Matcher      if (matcher.matches()) // Or whatever other matcher check     {          // Whatever processing     } } 

In the Java SE 6 JavaDoc for Matcher, one finds the option of reusing the same Matcher object, via the reset(CharSequence) method, which, as the source code shows, is a bit less expensive than creating a new Matcher every time, i.e., unlike above, one could do:

String expression = ...; // The Regular Expression Pattern pattern = Pattern.compile(expression); String[] ALL_INPUT = ...; // The large number of strings to be matched  Matcher matcher = pattern.matcher(""); // Declare and initialize a matcher  for (String input:ALL_INPUT) {     matcher.reset(input); // Reuse the same matcher      if (matcher.matches()) // Or whatever other matcher check     {          // Whatever processing     } } 

Should one use the reset(CharSequence) pattern above, or should they prefer to initialize a new Matcher object every time?

Answer 1

By all means reuse the Matcher. The only good reason to create a new Matcher is to ensure thread-safety. That's why you don't make a public static Matcher m—in fact, that's the reason a separate, thread-safe Pattern factory object exists in the first place.

In every situation where you are sure there's only one user of Matcher at any point in time, it is OK to reuse it with reset.