What's the difference between String.matches and Matcher.matches?

Question

What\'s the difference between String.matches and Matcher.matches? Is there any difference in terms of performance or other things?

Answer 1

Out of curiosity I did this small test on the time differences. Turns out that using a pre-compiled pattern is more than 5 times faster than using String.matches method.

import java.util.regex.Pattern;

/**
 * @author Rajind Ruparathna
 */
public class MatchesTest {
    public static void main(String Args[]) {
        String first = "@\\{message.headers\\.?([^\\}]*)\\}";
        String second = "@\\{message.headers.wolla\\}";
        long start, end, total;
        float avg;
        int NUM_OF_ITERATIONS = 100;

        Pattern pattern = Pattern.compile(first);

        total = 0;
        start = 0;
        end = 0;
        avg = 0;

        for (int i=0; i< NUM_OF_ITERATIONS; i++) {
            start = System.nanoTime();
            pattern.matcher(second).matches();
            end = System.nanoTime();
            total = total + (end - start);
        }
        avg = total/NUM_OF_ITERATIONS;
        System.out.println("Duration pre compiled: " + avg);

        total = 0;
        start = 0;
        end = 0;
        avg = 0;

        for (int i=0; i< NUM_OF_ITERATIONS; i++) {
            start = System.nanoTime();
            first.matches(second);
            end = System.nanoTime();
            total = total + (end - start);
        }
        avg = total/NUM_OF_ITERATIONS;
        System.out.println("In place compiled: " + avg);
    }
}

Output (nanoseconds):

Duration pre compiled: 4505.0

In place compiled:    44960.0

P.S. This test is a quick and dirty test and may not be according to performance benchmarking practises. If you want to get highly accurate results please use a micro benchmarking tool.