Question

Trying to efficiently extract some numbers from a string and have tried

• java.util.regex.Matcher
• com.google.common.base.Splitter

The results were :

• via Regular Expression: 24417 ms
• via Google Splitter: 17730 ms

Is there another faster way you can recommend ?

I know similar questions asked before e.g. How to extract multiple integers from a String in Java? but my emphasis is on making this fast (but maintainable/simple) as it happens a lot.

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EDIT : Here are my final results which tie in with those from Andrea Ligios below:

• Regular Expression (without brackets) : 18857
• Google Splitter (without the superflous trimResults() method): 15329
• Martijn Courteaux answer below: 4073

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import org.junit.Test;

import com.google.common.base.CharMatcher;
import com.google.common.base.Splitter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Sample {

    final static int COUNT = 50000000;
    public static final String INPUT = "FOO-1-9-BAR1"; // I want 1, 9, 1

    @Test
    public void extractNumbers() {
        long startTime = System.currentTimeMillis();
        for (int i = 0; i < COUNT; i++) {
            // Output is list of 1, 9, 1
            Demo.extractNumbersViaGoogleSplitter(INPUT);
        }
        System.out.println("Total execution time (ms) via Google Splitter: " + (System.currentTimeMillis() - startTime));


        startTime = System.currentTimeMillis();
        for (int i = 0; i < COUNT; i++) {
            // Output is list of 1, 9, 1
            Demo.extractNumbersViaRegEx(INPUT);
        }
        System.out.println("Total execution time (ms) Regular Expression: " + (System.currentTimeMillis() - startTime));

    }
}

class Demo {

    static List<Integer> extractNumbersViaGoogleSplitter(final String text) {

        Iterator<String> iter = Splitter.on(CharMatcher.JAVA_DIGIT.negate()).trimResults().omitEmptyStrings().split(text).iterator();
        final List<Integer> result = new ArrayList<Integer>();
        while (iter.hasNext()) {
            result.add(Integer.parseInt(iter.next()));

        }
        return result;
    }
    /**
     * Matches all the numbers in a string, as individual groups. e.g.
     * FOO-1-BAR1-1-12 matches 1,1,1,12.
     */
    private static final Pattern NUMBERS = Pattern.compile("(\\d+)");

    static List<Integer> extractNumbersViaRegEx(final String source) {
        final Matcher matcher = NUMBERS.matcher(source);
        final List<Integer> result = new ArrayList<Integer>();

        if (matcher.find()) {
            do {
                result.add(Integer.parseInt(matcher.group(0)));
            } while (matcher.find());
            return result;
        }
        return result;
    }
}

Answer 1

This is a very quick algorithm:

public List<Integer> extractIntegers(String input)
{
    List<Integer> result = new ArrayList<Integer>();
    int index = 0;
    int v = 0;
    int l = 0;
    while (index < input.length())
    {
        char c = input.charAt(index);
        if (Character.isDigit(c))
        {
            v *= 10;
            v += c - '0';
            l++;
        } else if (l > 0)
        {
            result.add(v);
            l = 0;
            v = 0;
        }
        index++;
    }
    if (l > 0)
    {
        result.add(v);
    }
    return result;
}

This code took on my machine 3672 milliseconds, for “FOO-1-9-BAR1” and 50000000 runs. I’m on a 2.3 GHz core.