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BAEL-1464 Guava Memoizer (#3420) 

* BAEL-1464 Guava Memoizer

* Update codes based on code review and discussion in JIRA
This commit is contained in:
Aprian Diaz Novandi 2018-01-29 09:26:15 +01:00 committed by Grzegorz Piwowarek
parent 829c0414fe
commit d1a4848cb4
4 changed files with 163 additions and 0 deletions
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17
guava/src/main/java/org/baeldung/guava/memoizer/CostlySupplier.java Normal file
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package org.baeldung.guava.memoizer;
import java.math.BigInteger;
import java.util.Random;
import java.util.concurrent.TimeUnit;
public class CostlySupplier {
public static BigInteger generateBigNumber() {
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
}
return new BigInteger("12345");
}
}

22
guava/src/main/java/org/baeldung/guava/memoizer/Factorial.java Normal file
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package org.baeldung.guava.memoizer;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import java.math.BigInteger;
public class Factorial {
private static LoadingCache<Integer, BigInteger> memo = CacheBuilder.newBuilder()
.build(CacheLoader.from(Factorial::getFactorial));
public static BigInteger getFactorial(int n) {
if (n == 0) {
return BigInteger.ONE;
} else {
return BigInteger.valueOf(n).multiply(memo.getUnchecked(n - 1));
}
}
}

26
guava/src/main/java/org/baeldung/guava/memoizer/FibonacciSequence.java Normal file
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package org.baeldung.guava.memoizer;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import java.math.BigInteger;
import java.util.concurrent.TimeUnit;
public class FibonacciSequence {
private static LoadingCache<Integer, BigInteger> memo = CacheBuilder.newBuilder()
.maximumSize(100)
.build(CacheLoader.from(FibonacciSequence::getFibonacciNumber));
public static BigInteger getFibonacciNumber(int n) {
if (n == 0) {
return BigInteger.ZERO;
} else if (n == 1) {
return BigInteger.ONE;
} else {
return memo.getUnchecked(n - 1).add(memo.getUnchecked(n - 2));
}
}
}

98
guava/src/test/java/org/baeldung/guava/GuavaMemoizerUnitTest.java Normal file
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package org.baeldung.guava;
import com.google.common.base.Suppliers;
import org.baeldung.guava.memoizer.CostlySupplier;
import org.baeldung.guava.memoizer.Factorial;
import org.baeldung.guava.memoizer.FibonacciSequence;
import org.junit.Test;
import java.math.BigInteger;
import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.TimeUnit;
import java.util.function.Supplier;
import static org.hamcrest.core.Is.is;
import static org.hamcrest.core.IsEqual.equalTo;
import static org.hamcrest.number.IsCloseTo.closeTo;
import static org.junit.Assert.assertThat;
public class GuavaMemoizerUnitTest {
@Test
public void givenInteger_whenGetFibonacciNumber_thenShouldCalculateFibonacciNumber() {
// given
int n = 95;
// when
BigInteger fibonacciNumber = FibonacciSequence.getFibonacciNumber(n);
// then
BigInteger expectedFibonacciNumber = new BigInteger("31940434634990099905");
assertThat(fibonacciNumber, is(equalTo(expectedFibonacciNumber)));
}
@Test
public void givenInteger_whenGetFactorial_thenShouldCalculateFactorial() {
// given
int n = 95;
// when
BigInteger factorial = new Factorial().getFactorial(n);
// then
BigInteger expectedFactorial = new BigInteger("10329978488239059262599702099394727095397746340117372869212250571234293987594703124871765375385424468563282236864226607350415360000000000000000000000");
assertThat(factorial, is(equalTo(expectedFactorial)));
}
@Test
public void givenMemoizedSupplier_whenGet_thenSubsequentGetsAreFast() {
Supplier<BigInteger> memoizedSupplier;
memoizedSupplier = Suppliers.memoize(CostlySupplier::generateBigNumber);
Instant start = Instant.now();
BigInteger bigNumber = memoizedSupplier.get();
Long durationInMs = Duration.between(start, Instant.now()).toMillis();
assertThat(bigNumber, is(equalTo(new BigInteger("12345"))));
assertThat(durationInMs.doubleValue(), is(closeTo(2000D, 100D)));
start = Instant.now();
bigNumber = memoizedSupplier.get().add(BigInteger.ONE);
durationInMs = Duration.between(start, Instant.now()).toMillis();
assertThat(bigNumber, is(equalTo(new BigInteger("12346"))));
assertThat(durationInMs.doubleValue(), is(closeTo(0D, 100D)));
start = Instant.now();
bigNumber = memoizedSupplier.get().add(BigInteger.TEN);
durationInMs = Duration.between(start, Instant.now()).toMillis();
assertThat(bigNumber, is(equalTo(new BigInteger("12355"))));
assertThat(durationInMs.doubleValue(), is(closeTo(0D, 100D)));
}
@Test
public void givenMemoizedSupplierWithExpiration_whenGet_thenSubsequentGetsBeforeExpiredAreFast() throws InterruptedException {
Supplier<BigInteger> memoizedSupplier;
memoizedSupplier = Suppliers.memoizeWithExpiration(CostlySupplier::generateBigNumber, 3, TimeUnit.SECONDS);
Instant start = Instant.now();
BigInteger bigNumber = memoizedSupplier.get();
Long durationInMs = Duration.between(start, Instant.now()).toMillis();
assertThat(bigNumber, is(equalTo(new BigInteger("12345"))));
assertThat(durationInMs.doubleValue(), is(closeTo(2000D, 100D)));
start = Instant.now();
bigNumber = memoizedSupplier.get().add(BigInteger.ONE);
durationInMs = Duration.between(start, Instant.now()).toMillis();
assertThat(bigNumber, is(equalTo(new BigInteger("12346"))));
assertThat(durationInMs.doubleValue(), is(closeTo(0D, 100D)));
TimeUnit.SECONDS.sleep(1);
start = Instant.now();
bigNumber = memoizedSupplier.get().add(BigInteger.TEN);
durationInMs = Duration.between(start, Instant.now()).toMillis();
assertThat(bigNumber, is(equalTo(new BigInteger("12355"))));
assertThat(durationInMs.doubleValue(), is(closeTo(2000D, 100D)));
}
}