Benchmark for http://stackoverflow.com/questions/1102891/how-to-check-if-a-string-is-numeric-in-java/

Main.java

/*
 Output:
100000 digits
     3 ms | regex
     9 ms | lambda
    11 ms | StringUtils

1000000 digits
     8 ms | regex
     9 ms | lambda
     2 ms | StringUtils

10000000 digits
   128 ms | regex
    56 ms | lambda
    17 ms | StringUtils

100000000 digits
   690 ms | regex
   510 ms | lambda
   161 ms | StringUtils

50M-long random string
   599 ms | regex
   248 ms | lambda
    77 ms | StringUtils 
 */

import org.apache.commons.lang3.RandomStringUtils;
import org.apache.commons.lang3.StringUtils;

import java.util.ArrayList;
import java.util.List;

public class Main {

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

    public static class TestCase {
        public String string;
        public String name;

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

        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 stringUtilsChecker = new NumericChecker() {
        @Override
        public boolean isNumeric(String string) {
            return StringUtils.isNumeric(string);
        }
    };

    public static void main(String[] args) {
        int[] size = {100000, 1000000, 10000000, 100000000};
        List<TestCase> tests = new ArrayList<>();

        // Pure numbers
        for (int N : size) {
            String string = RandomStringUtils.randomNumeric(N);
            tests.add(new TestCase(string, String.format("%s digits", N)));
        }

        // 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, "50M-long random string"));

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

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

            System.out.println(test.name);
            System.out.printf("%6d ms | regex \n", runTimeRegex);
            System.out.printf("%6d ms | lambda \n", runTimeLambda);
            System.out.printf("%6d ms | StringUtils \n\n", runTimeStringUtils);
        }
    }

}