This program checks whether a given random number is primitive or not.

Run the program and also make a profiling recording.

java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=60s,name=Hotmethods,filename=hotmethods.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/hotmethods.jar

In Code -> Hot Methods tab, you should see that the program has spent a lot of time in the LinkedList.indexOf(Object) method, which is called from contains method.

By changing LinkedList to a HashSet, you can make the program run a lot faster.

The contains methods in Linked List checks all the items. Algorithm run time is O(n). However the HashSet contains algorithm's run time is O(1).

In the program, change Collection<Integer> primeNumbers = new LinkedList<>() to Collection<Integer> primeNumbers = new HashSet<>() to use a HashSet for Prime Numbers

Check the runtime using HashSet.

Use time command in Linux to measure the time.