Example5PrimesCachingMap.java

/**
 * Copyright 2009-2013 the original author or authors.
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.javacrumbs.geecon;

import static java.lang.Math.sqrt;
import static java.util.stream.IntStream.range;
import static java.util.stream.LongStream.rangeClosed;
import static net.javacrumbs.common.Utils.log;
import static net.javacrumbs.common.Utils.measure;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.function.Function;

public class Example5PrimesCachingMap {
    private final ConcurrentMap<Integer, Boolean> isPrime = new ConcurrentHashMap<>();


    public static void main(String[] args) throws InterruptedException, ExecutionException {
        new Example5PrimesCachingMap().doRun();
    }

    private void doRun() throws InterruptedException, ExecutionException {
        measure(() -> log(countPrimes(1_000_000, 2_000_000)));
        measure(() -> log(countPrimes(1_000_000, 2_000_000)));
    }

    private long countPrimes(int from, int to) {
        return range(from, to)
                .filter(this::isPrime)
                .parallel()
                .count();
    }

    public boolean isPrime(int i) {
        return isPrime.computeIfAbsent(i, this::calculateIsPrime);
    }

    private boolean calculateIsPrime(int n) {
        return n > 1 && rangeClosed(2, (long) sqrt(n)).noneMatch(divisor -> n % divisor == 0);
    }
}