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July 27, 2021 11:05
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Java Prime Numbers (Educational)
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| Welcome to an amazing prime number app! | |
| Please enter an integer between 1 and 1000000. Enter 'generate' to generate all. Enter 'quit' to exit. | |
| generate | |
| Testing if 1 is a prime... | |
| [DEBUG]: User input '1' missed the cache, which contains 0 entries. | |
| [DEBUG]: Operation took 21889 µs | |
| It's NOT a prime! | |
| Testing if 2 is a prime... | |
| [DEBUG]: User input '2' missed the cache, which contains 1 entries. | |
| [DEBUG]: Operation took 201 µs | |
| It's a prime! | |
| Testing if 3 is a prime... | |
| [DEBUG]: User input '3' missed the cache, which contains 2 entries. | |
| [DEBUG]: Operation took 155 µs | |
| It's a prime! | |
| Testing if 4 is a prime... | |
| [DEBUG]: User input '4' missed the cache, which contains 3 entries. | |
| [DEBUG]: Operation took 155 µs | |
| It's NOT a prime! | |
| Testing if 5 is a prime... | |
| [DEBUG]: User input '5' missed the cache, which contains 4 entries. | |
| [DEBUG]: Operation took 181 µs | |
| It's a prime! | |
| Testing if 6 is a prime... | |
| [DEBUG]: User input '6' missed the cache, which contains 5 entries. | |
| [DEBUG]: Operation took 144 µs | |
| It's NOT a prime! | |
| Testing if 7 is a prime... | |
| [DEBUG]: User input '7' missed the cache, which contains 6 entries. | |
| [DEBUG]: Operation took 151 µs | |
| It's a prime! | |
| Testing if 8 is a prime... | |
| [DEBUG]: User input '8' missed the cache, which contains 7 entries. | |
| [DEBUG]: Operation took 145 µs | |
| It's NOT a prime! | |
| Testing if 9 is a prime... | |
| [DEBUG]: User input '9' missed the cache, which contains 8 entries. | |
| [DEBUG]: Operation took 147 µs | |
| It's NOT a prime! | |
| Testing if 10 is a prime... | |
| [DEBUG]: User input '10' missed the cache, which contains 9 entries. | |
| [DEBUG]: Operation took 132 µs | |
| It's NOT a prime! | |
| (999980 primes skipped) | |
| Testing if 999990 is a prime... | |
| [DEBUG]: User input '999990' missed the cache, which contains 999989 entries. | |
| [DEBUG]: Operation took 4 µs | |
| It's NOT a prime! | |
| Testing if 999991 is a prime... | |
| [DEBUG]: User input '999991' missed the cache, which contains 999990 entries. | |
| [DEBUG]: Operation took 5 µs | |
| It's NOT a prime! | |
| Testing if 999992 is a prime... | |
| [DEBUG]: User input '999992' missed the cache, which contains 999991 entries. | |
| [DEBUG]: Operation took 5 µs | |
| It's NOT a prime! | |
| Testing if 999993 is a prime... | |
| [DEBUG]: User input '999993' missed the cache, which contains 999992 entries. | |
| [DEBUG]: Operation took 4 µs | |
| It's NOT a prime! | |
| Testing if 999994 is a prime... | |
| [DEBUG]: User input '999994' missed the cache, which contains 999993 entries. | |
| [DEBUG]: Operation took 4 µs | |
| It's NOT a prime! | |
| Testing if 999995 is a prime... | |
| [DEBUG]: User input '999995' missed the cache, which contains 999994 entries. | |
| [DEBUG]: Operation took 5 µs | |
| It's NOT a prime! | |
| Testing if 999996 is a prime... | |
| [DEBUG]: User input '999996' missed the cache, which contains 999995 entries. | |
| [DEBUG]: Operation took 4 µs | |
| It's NOT a prime! | |
| Testing if 999997 is a prime... | |
| [DEBUG]: User input '999997' missed the cache, which contains 999996 entries. | |
| [DEBUG]: Operation took 5 µs | |
| It's NOT a prime! | |
| Testing if 999998 is a prime... | |
| [DEBUG]: User input '999998' missed the cache, which contains 999997 entries. | |
| [DEBUG]: Operation took 4 µs | |
| It's NOT a prime! | |
| Testing if 999999 is a prime... | |
| [DEBUG]: User input '999999' missed the cache, which contains 999998 entries. | |
| [DEBUG]: Operation took 3 µs | |
| It's NOT a prime! | |
| Testing if 1000000 is a prime... | |
| [DEBUG]: User input '1000000' missed the cache, which contains 999999 entries. | |
| [DEBUG]: Operation took 5 µs | |
| It's NOT a prime! | |
| (Notice the operation time and how much impact JVM "warmup" has) |
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| (Now the JVM has sped up the process so significantly, we can't even measure the operation in microseconds most of the time) | |
| (Skipped to end of output) | |
| Testing if 999980 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999981 is a prime... | |
| [DEBUG]: Operation took 1 µs | |
| It's NOT a prime! | |
| Testing if 999982 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999983 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's a prime! | |
| Testing if 999984 is a prime... | |
| [DEBUG]: Operation took 1 µs | |
| It's NOT a prime! | |
| Testing if 999985 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999986 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999987 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999988 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999989 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999990 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999991 is a prime... | |
| [DEBUG]: Operation took 1 µs | |
| It's NOT a prime! | |
| Testing if 999992 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999993 is a prime... | |
| [DEBUG]: Operation took 1 µs | |
| It's NOT a prime! | |
| Testing if 999994 is a prime... | |
| [DEBUG]: Operation took 1 µs | |
| It's NOT a prime! | |
| Testing if 999995 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999996 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999997 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999998 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 999999 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! | |
| Testing if 1000000 is a prime... | |
| [DEBUG]: Operation took 0 µs | |
| It's NOT a prime! |
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| Welcome to an amazing prime number app! | |
| Please enter an integer between 1 and 1000000. Enter 'generate' to generate all. Enter 'quit' to exit. | |
| 1337 | |
| Testing if 1337 is a prime... | |
| [DEBUG]: User input '1337' missed the cache, which contains 0 entries. | |
| [DEBUG]: Operation took 19850 µs | |
| It's NOT a prime! | |
| Please enter an integer between 1 and 1000000. Enter 'generate' to generate all. Enter 'quit' to exit. | |
| 1337 | |
| Testing if 1337 is a prime... | |
| [DEBUG]: Operation took 40 µs | |
| It's NOT a prime! | |
| Please enter an integer between 1 and 1000000. Enter 'generate' to generate all. Enter 'quit' to exit. | |
| (Notice the performance impact of memoization during the second computation) |
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| import java.time.Duration; | |
| import java.time.LocalDateTime; | |
| import java.time.temporal.ChronoUnit; | |
| import java.util.*; | |
| import java.util.concurrent.Callable; | |
| import java.util.function.Predicate; | |
| import java.util.function.UnaryOperator; | |
| import java.util.stream.IntStream; | |
| public class PrimesApp { | |
| static final int PRIMES_LOWER_BOUND = 1; | |
| static final int PRIMES_UPPER_BOUND = 1_000_000; | |
| static final String EXIT_COMMAND = "quit"; | |
| static final String GENERATE_COMMAND = "generate"; | |
| static final boolean DEBUG_ENABLED = true; | |
| private static final Scanner USER_INPUT = new Scanner(System.in); | |
| private static final Map<Integer, Boolean> PRIMES_CACHE = new HashMap<>(PRIMES_UPPER_BOUND); | |
| public static void main(String[] args) { | |
| System.out.println("Welcome to an amazing prime number app!"); | |
| checkPrimes(); | |
| } | |
| static Predicate<Integer> isWithinBounds() { | |
| return input -> input <= PRIMES_UPPER_BOUND && input >= PRIMES_LOWER_BOUND; | |
| } | |
| static Predicate<Integer> isPrimeNumber() { | |
| return input -> { | |
| if (input == 1) { | |
| return false; | |
| } | |
| if (input == 2 || input == 3) { | |
| return true; | |
| } | |
| if (input % 2 == 0) { | |
| return false; | |
| } | |
| final var inputSquared = (int) Math.sqrt(input) + 1; | |
| for (int i = 3; i < inputSquared; i += 2) { | |
| if (input % i == 0) { | |
| return false; | |
| } | |
| } | |
| return true; | |
| }; | |
| } | |
| static Predicate<String> isExitCommand() { | |
| return EXIT_COMMAND::equalsIgnoreCase; | |
| } | |
| static Predicate<String> isGenerateCommand() { | |
| return GENERATE_COMMAND::equalsIgnoreCase; | |
| } | |
| static <T> T measureExecution(Callable<T> command) { | |
| try { | |
| Objects.requireNonNull(command, "Parameter 'command' must not be null"); | |
| final var startedAt = LocalDateTime.now(); | |
| final var value = command.call(); | |
| final var executionDuration = Duration.between(startedAt, LocalDateTime.now()); | |
| debugLog("Operation took %s µs", executionDuration.dividedBy(ChronoUnit.MICROS.getDuration())); | |
| return value; | |
| } catch (Exception e) { | |
| exitFatally(e.getMessage()); | |
| return null; | |
| } | |
| } | |
| private static void checkPrimes() { | |
| final var userInput = readUserInput(); | |
| if (isWithinBounds().negate().test(userInput)) { | |
| exitFatally("Whoops! %d is outside allowed range (%d - %d)!", userInput, PRIMES_LOWER_BOUND, PRIMES_UPPER_BOUND); | |
| } | |
| doCheckPrime(userInput); | |
| checkPrimes(); | |
| } | |
| private static void doCheckPrime(int userInput) { | |
| System.out.printf("Testing if %d is a prime...%n", userInput); | |
| final var isPrime | |
| = measureExecution(() -> PRIMES_CACHE.computeIfAbsent(userInput, cacheMissed().andThen(isPrimeNumber()::test))); | |
| System.out.println(isPrime ? "It's a prime!" : "It's NOT a prime!"); | |
| } | |
| private static int readUserInput() { | |
| System.out.printf( | |
| "Please enter an integer between %d and %d. Enter '%s' to generate all. Enter '%s' to exit.%n", | |
| PRIMES_LOWER_BOUND, | |
| PRIMES_UPPER_BOUND, | |
| GENERATE_COMMAND, | |
| EXIT_COMMAND | |
| ); | |
| try { | |
| final var nextUserInput = USER_INPUT.nextLine(); | |
| if (isExitCommand().test(nextUserInput)) { | |
| exitNicely(); | |
| } else if (isGenerateCommand().test(nextUserInput)) { | |
| generateAllPrimes(); | |
| return readUserInput(); | |
| } | |
| return Integer.parseInt(nextUserInput); | |
| } catch (NumberFormatException e) { | |
| System.err.printf("It seems like you didn't enter an integer: %s%n", e.getMessage()); | |
| return readUserInput(); | |
| } catch (NoSuchElementException e) { | |
| // Be quiet 🤫 | |
| return 0; | |
| } | |
| } | |
| private static void generateAllPrimes() { | |
| IntStream.rangeClosed(PRIMES_LOWER_BOUND, PRIMES_UPPER_BOUND).forEach(PrimesApp::doCheckPrime); | |
| } | |
| private static void exitFatally(String errorMessage, Object... args) { | |
| System.err.printf(errorMessage + "%n", args); | |
| System.exit(1); | |
| } | |
| private static void exitNicely() { | |
| System.out.println("Have a nice day!"); | |
| System.exit(0); | |
| } | |
| private static UnaryOperator<Integer> cacheMissed() { | |
| return input -> { | |
| debugLog("User input '%d' missed the cache, which contains %d entries.", input, PRIMES_CACHE.size()); | |
| return input; | |
| }; | |
| } | |
| private static void debugLog(String message, Object... args) { | |
| if (DEBUG_ENABLED) { | |
| System.out.println("[DEBUG]: " + String.format(message, args)); | |
| } | |
| } | |
| } |
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| import org.junit.jupiter.api.Test; | |
| import org.junit.jupiter.params.ParameterizedTest; | |
| import org.junit.jupiter.params.provider.ValueSource; | |
| import static org.junit.jupiter.api.Assertions.*; | |
| class PrimesAppTest { | |
| @Test | |
| void lowerBound_lessThan_upperBound() { | |
| assertTrue(PrimesApp.PRIMES_LOWER_BOUND < PrimesApp.PRIMES_UPPER_BOUND); | |
| } | |
| @Test | |
| void lowerBound_upperBound_positive() { | |
| assertTrue(PrimesApp.PRIMES_LOWER_BOUND > 0); | |
| assertTrue(PrimesApp.PRIMES_UPPER_BOUND > 0); | |
| } | |
| @Test | |
| void isWithinBounds_insideBounds() { | |
| final var input = PrimesApp.PRIMES_LOWER_BOUND + 100; | |
| final var isWithinBounds = PrimesApp.isWithinBounds().test(input); | |
| assertTrue(isWithinBounds); | |
| } | |
| @Test | |
| void isWithinBounds_outsideBounds() { | |
| final var input = PrimesApp.PRIMES_UPPER_BOUND + 100; | |
| final var isWithinBounds = PrimesApp.isWithinBounds().test(input); | |
| assertFalse(isWithinBounds); | |
| } | |
| @ParameterizedTest | |
| @ValueSource(ints = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29}) | |
| void isPrimeNumber_primes(int prime) { | |
| final var isPrime = PrimesApp.isPrimeNumber().test(prime); | |
| assertTrue(isPrime); | |
| } | |
| @ParameterizedTest | |
| @ValueSource(ints = {4, 6, 8, 9, 10, 12, 14, 15, 16, 18}) | |
| void isPrimeNumber_nonPrimes(int nonPrime) { | |
| final var isPrime = PrimesApp.isPrimeNumber().test(nonPrime); | |
| assertFalse(isPrime); | |
| } | |
| } |
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