Performance difference between CollectionUtils.isNotEmpty and In Place check

Question

Recently while I was doing a micro-benchmark , I noticed that the CollectionUtils.isNotEmpty method consumed more time. I thought there might be a typo or oversight from me. I replaced the code with in place check of collection is not null and size is greater than zero. It proved to be much faster.

I pulled the source code of method CollectionUtils.isNotEmpty into my code and it is faster as well.

What causes this difference?

Note: I know micro-benchmark is not going to help in the whole realm of JVM optimization. I specifically put for 100 times in the loop , if it is more than JVM is going to optimize it. Checked the code in Windows and Linux and the performance difference is similar.

import java.util.Arrays;
import java.util.Collection;
import java.util.List;

import org.apache.commons.collections4.CollectionUtils;

public class TestCollectionUtilsPerf {

public static void main(String[] args) {
    List<String> stringList = Arrays
            .asList(new String[] { "StringOne", "StringTwo", "StringThree", "StringFour", "StringFive" });

    long startTime = System.nanoTime();
    for (int i = 0; i < 100; i++) {
        if (stringList != null && stringList.size() != 0) {
            continue;
        }
    }

    System.out.format("Manual Inplace Check Time taken is : %d µs %n", (System.nanoTime() - startTime) / 1000);

    startTime = System.nanoTime();
    for (int i = 0; i < 100; i++) {
        if (CollectionUtils.isNotEmpty(stringList)) {
            continue;
        }
    }

    System.out.format("Collection Utils Time taken is     : %d µs %n", (System.nanoTime() - startTime) / 1000);

    startTime = System.nanoTime();
    for (int i = 0; i < 100; i++) {
        if (isNotEmpty(stringList)) {
            continue;
        }
    }

    System.out.format("Manual Method Check Time taken is  : %d µs %n", (System.nanoTime() - startTime) / 1000);

}

public static boolean isEmpty(final Collection<?> coll) {
    return coll == null || coll.isEmpty();
}

public static boolean isNotEmpty(final Collection<?> coll) {
    return !isEmpty(coll);
}

}

Output :

Manual Inplace Check Time taken is : 61 µs
Collection Utils Time taken is : 237193 µs
Manual Method Check Time taken is : 66 µs

Answer 1

Maybe It took a lot of time to load the class or the jar package,You can try to call CollectionUtils.isEmpty at the very beginning.

public static void main(String[] args) {
    List<String> stringList = Arrays
            .asList(new String[] { "StringOne", "StringTwo", "StringThree", "StringFour", "StringFive" });
    //try it at the begging to load the class
    CollectionUtils.isEmpty(stringList);
    ......

}

and my outbut

Manual Inplace Check Time taken is : 10 µs 
Collection Utils Time taken is     : 21 µs 
Manual Method Check Time taken is  : 25 µs