java 下计算质数的多线程跟单线程执行代码分析

public abstract class AbstractPrimeFinder {
public boolean isPrime(final int number) {
if (number <= 1)
return false;
for (int i = 2; i <= Math.sqrt(number); i++)
if (number % i == 0)
return false;
return true;
}

public int countPrimesInRange(final int lower, final int upper) {
int total = 0;
for (int i = lower; i <= upper; i++)
if (isPrime(i))
total++;
return total;
}

public void timeAndCompute(final int number) {
final long start = System.nanoTime();
final long numberOfPrimes = countPrimes(number);
final long end = System.nanoTime();
System.out.printf("Number of primes under %d is %d\n", number,
numberOfPrimes);
System.out.println("Time (seconds) taken is " + (end - start) / 1.0e9);
}

public abstract int countPrimes(final int number);
}

public class SequentialPrimeFinder extends AbstractPrimeFinder {
public int countPrimes(final int number) {
return countPrimesInRange(1, number);
}

public static void main(final String[] args) {
new SequentialPrimeFinder().timeAndCompute(10000000);
}
}

Number of primes under 10000000 is 664579
Time (seconds) taken is 7.518444261

package com.mime;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class ConcurrentPrimeFinder extends AbstractPrimeFinder {
private final int poolSize;
private final int numberOfParts;

public ConcurrentPrimeFinder(final int thePoolSize,
final int theNumberOfParts) {
poolSize = thePoolSize;
numberOfParts = theNumberOfParts;
}

public int countPrimes(final int number) {
int count = 0;
try {
final List<Callable<Integer>> partitions = new ArrayList<Callable<Integer>>();
final int chunksPerPartition = number / numberOfParts;
for (int i = 0; i < numberOfParts; i++) {
final int lower = (i * chunksPerPartition) + 1;
final int upper = (i == numberOfParts - 1) ? number : lower
+ chunksPerPartition - 1;
partitions.add(new Callable<Integer>() {
public Integer call() {
return countPrimesInRange(lower, upper);
}
});
}
final ExecutorService executorPool = Executors
.newFixedThreadPool(poolSize);
final List<Future<Integer>> resultFromParts = executorPool
.invokeAll(partitions, 10000, TimeUnit.SECONDS);
executorPool.shutdown();
for (final Future<Integer> result : resultFromParts)
count += result.get();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
return count;
}

public static void main(final String[] args) {
new ConcurrentPrimeFinder(4,100).timeAndCompute(10000000);
}

}

Number of primes under 10000000 is 664579
Time (seconds) taken is 3.825282456