Benchmark for http://stackoverflow.com/questions/15111420/how-to-check-if-a-string-contains-only-digits-in-java

Main.java

public class Main {

    public interface NumericChecker {
        boolean isNumeric(String string);
    }

    public static class TestCase {
        public String string;

        public TestCase(String string) {
            this.string = string;
        }

        long runWith(NumericChecker checker) {
            long startTime = System.nanoTime();
            checker.isNumeric(string);
            long stopTime  = System.nanoTime();
            return (stopTime - startTime) / 1000000;
        }

    }

    public static NumericChecker regexChecker = new NumericChecker() {
	    private String regex = "\\d+";

        @Override
        public boolean isNumeric(String string) {
            return string.matches(regex);
        }
    };

    public static NumericChecker lamdaChecker = new NumericChecker() {
        @Override
        public boolean isNumeric(String string) {
            return string.chars().allMatch(x -> Character.isDigit(x));
        }
    };

    public static NumericChecker parallelChecker = new NumericChecker() {
        @Override
        public boolean isNumeric(String string) {
            return string.chars().parallel().allMatch(x -> Character.isDigit(x));
        }
    };

    public static void main(String[] args) {
        int[] size = {500000, 5000000, 50000000, 100000000};
        List<TestCase> tests = new ArrayList<>();

        // Pure numbers
        for (int N : size) {
            String string = RandomStringUtils.randomNumeric(N);
            tests.add(new TestCase(string));
        }

        // Not a number, adding just for the sake of diversity
        String string = new StringBuilder().append(RandomStringUtils.randomNumeric(50000000))
                                           .append("foobar")
            	                           .append(RandomStringUtils.randomNumeric(50000000))
            	                           .toString();
        tests.add(new TestCase(string));

        // Warm-up JIT compiler
        for (TestCase test : tests.subList(0, 1)) {
            test.runWith(regexChecker);
            test.runWith(lamdaChecker);
            test.runWith(parallelChecker);
        }

        for (TestCase test : tests) {
            long runTimeRegex = test.runWith(regexChecker);
            long runTimeLambda = test.runWith(lamdaChecker);
            long runTimeParallel = test.runWith(parallelChecker);

            System.out.printf("%6d ms\n", runTimeRegex);
            System.out.printf("%6d ms\n", runTimeLambda);
            System.out.printf("%6d ms\n\n", runTimeParallel);
        }
    }

}

/*
 Output:
     4 ms
     2 ms
    10 ms

    33 ms
    21 ms
    18 ms

   285 ms
   224 ms
   210 ms

   571 ms
   465 ms
   360 ms

   537 ms
   232 ms
   227 ms
 */