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提交第七章代码
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‎chap7/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>node</artifactId>
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<groupId>xin.codedream.java8</groupId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>chap7</artifactId>
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</project>

‎chap7/src/main/java/xin/codedream/java8/chap7/ParallelStreams.java‎

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package xin.codedream.java8.chap7;
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import java.util.stream.LongStream;
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import java.util.stream.Stream;
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/**
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* ParallelStreams
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*
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* @author NGLSL
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* @date 2018/10/6
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*/
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public class ParallelStreams {
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public static long sequentialSum(long n) {
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// 生成自然数无限流
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return Stream.iterate(1L, i -> i + 1)
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// 限制到前n个数
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.limit(n)
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// 对所有数字求和来归纳流
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.reduce(0L, Long::sum);
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}
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public static long iterativeSum(long n) {
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long result = 0;
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for (long i = 0; i <= n; i++) {
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result += i;
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}
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return result;
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}
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public static long parallelSum(long n) {
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// 生成自然数无限流
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return Stream.iterate(1L, i -> i + 1)
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// 限制到前n个数
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.limit(n)
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// 将流转为并行流
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.parallel()
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// 对所有数字求和来归纳流
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.reduce(0L, Long::sum);
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}
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public static long rangedSum(long n) {
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return LongStream.rangeClosed(1, n)
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.reduce(0L, Long::sum);
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}
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public static long parallelRangedSum(long n) {
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return LongStream.rangeClosed(1, n)
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.parallel()
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.reduce(0L, Long::sum);
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}
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}

‎chap7/src/main/java/xin/codedream/java8/chap7/ParallelStreamsHarness.java‎

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package xin.codedream.java8.chap7;
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import java.util.function.Function;
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/**
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* ParallelStreamsHarness
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*
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* @author NGLSL
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* @date 2018/10/6
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*/
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public class ParallelStreamsHarness {
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public static void main(String[] args) {
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/*System.out.println("Sequential sum done in:" +
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measureSumPerf(ParallelStreams::sequentialSum, 10_000_000) + " msecs");*/
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/*System.out.println("Iterative sum done in:" +
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measureSumPerf(ParallelStreams::iterativeSum, 10_000_000) + " msecs");*/
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/*System.out.println("Parallel sum done in: " +
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measureSumPerf(ParallelStreams::parallelSum, 10_000_000) + " msecs");*/
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/*System.out.println("Ranged sum done in: " +
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measureSumPerf(ParallelStreams::rangedSum, 10_000_000) + " msecs");*/
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System.out.println("Parallel range sum done in:" +
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measureSumPerf(ParallelStreams::parallelRangedSum, 10_000_000) +
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" msecs");
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}
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public static long measureSumPerf(Function<Long, Long> adder, long n) {
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long fastest = Long.MAX_VALUE;
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for (int i = 0; i < 10; i++) {
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long start = System.nanoTime();
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long sum = adder.apply(n);
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long duration = (System.nanoTime() - start) / 1_000_000;
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System.out.println("Result: " + sum);
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if (duration < fastest) {
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fastest = duration;
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}
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}
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return fastest;
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}
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}

‎pom.xml‎

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<module>chap4</module>
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<module>chap5</module>
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<module>chap6</module>
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<module>chap7</module>
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</modules>
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</project>

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