JMH example 2018-11-30 05:02
Java Microbenchmark Harness is a good tool to test your code. It can tell you the code is efficiently or not. Today I will show you how to use it to test your code. Let's say you want to implement a functionality about probability. Maybe you want your program have a 1/10 probability of doing something. You have two ways to implement this.
- Use
ThreadLocalRandom.current().nextInt(10) == 1 - Use
num % 10 == 1
Then the next question is which one is more efficient?
The answer is "Test and compare them!". Here is the JMH code.
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@State(Scope.Benchmark)
public class JMHModClient {
private int[] numbers;
public static void main(String[] args) throws RunnerException {
Options opt = new OptionsBuilder()
.include(JMHModClient.class.getSimpleName())
.forks(2)
.warmupIterations(5)
.measurementIterations(5)
.build();
new Runner(opt).run();
}
@Benchmark
public void mod() {
int i = 0;
for (int num : numbers) {
if (num % 10 == 1) {
i++;
}
}
System.out.println(i);
}
@Benchmark
public void random() {
int i = 0;
for (int num : numbers) {
if (ThreadLocalRandom.current().nextInt(10) == 1) {
i++;
}
}
System.out.println(i);
}
@Setup
public void setUp() {
numbers = IntStream.rangeClosed(1, 1000).toArray();
}
}
Before run JMH code you need add maven dependency in you pom.xml.
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-core</artifactId>
<version>1.14.1</version>
</dependency>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-generator-annprocess</artifactId>
<version>1.14.1</version>
<scope>provided</scope>
</dependency>
The part of result is here
# Run complete. Total time: 00:00:42
Benchmark Mode Cnt Score Error Units
JMHModClient.mod avgt 10 34.935 ± 0.818 us/op
JMHModClient.random avgt 10 39.888 ± 3.123 us/op
We can see mod function is a little better than random. "Error" column has nothing. "Score" column show the result with "+0.818".
EOF