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brianwaybrianway
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[add] add ToListCollector and CollectorHarness
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3 files changed

+112
-12
lines changed

3 files changed

+112
-12
lines changed

‎java8/src/main/java/com/brianway/learning/java8/streamapi/CollectorHarness.java

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package com.brianway.learning.java8.streamapi;
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import java.util.function.Consumer;
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/**
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* 比较收集器的性能
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*/
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public class CollectorHarness {
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public static void main(String[] args) {
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System.out.println("Partitioning done in: " + execute(PartitionPrimeNumbers::partitionPrimes) + " msecs");
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System.out.println("Partitioning done in: " + execute(PartitionPrimeNumbers::partitionPrimesWithCustomCollector) + " msecs");
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}
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private static long execute(Consumer<Integer> primePartitioner) {
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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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primePartitioner.accept(1_000_000);
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long duration = (System.nanoTime() - start) / 1_000_000;
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if (duration < fastest) fastest = duration;
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System.out.println("done in " + duration);
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}
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return fastest;
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/streamapi/PartitionPrimeNumbers.java

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@@ -20,13 +20,17 @@
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import java.util.stream.Stream;
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/**
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* 分区:分类的特殊情况。分区函数返回一个布尔值
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* 得到 100 以内的质数和非质数
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*
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* - 分区:分类的特殊情况。分区函数返回一个布尔值
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* - Collector
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*/
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public class PartitionPrimeNumbers {
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public static void main(String... args) {
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System.out.println("Numbers partitioned in prime and non-prime: " + partitionPrimes(100));
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System.out.println("Numbers partitioned in prime and non-prime: " + partitionPrimesWithCustomCollector(100));
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System.out.println("Numbers partitioned in prime and non-prime: " + partitionPrimesWithInlineCollector(100));
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}
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@@ -62,22 +66,29 @@ public static <A> List<A> takeWhile(List<A> list, Predicate<A> p) {
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return list;
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}
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/**
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* Collector
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* 1.建立新的结果容器: supplier 方法
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* 2.将元素添到结果容器: accumulator 方法
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* 3.对容器应用最终转换: finisher 方法
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* 4.合并两个结果容器: combiner
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* 5.characteristics 方法
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*/
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public static class PrimeNumbersCollector
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implements Collector<Integer, Map<Boolean, List<Integer>>, Map<Boolean, List<Integer>>> {
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@Override
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public Supplier<Map<Boolean, List<Integer>>> supplier() {
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return () -> new HashMap<Boolean, List<Integer>>() {{
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put(true, new ArrayList<Integer>());
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put(false, new ArrayList<Integer>());
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put(true, new ArrayList<>());
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put(false, new ArrayList<>());
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}};
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}
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@Override
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public BiConsumer<Map<Boolean, List<Integer>>, Integer> accumulator() {
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return (Map<Boolean, List<Integer>> acc, Integer candidate) -> {
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acc.get(isPrime(acc.get(true),
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candidate))
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acc.get(isPrime(acc.get(true), candidate))
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.add(candidate);
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};
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}
@@ -102,17 +113,17 @@ public Set<Characteristics> characteristics() {
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}
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}
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public Map<Boolean, List<Integer>> partitionPrimesWithInlineCollector(int n) {
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public static Map<Boolean, List<Integer>> partitionPrimesWithInlineCollector(int n) {
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return Stream.iterate(2, i -> i + 1).limit(n)
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.collect(
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() -> new HashMap<Boolean, List<Integer>>() {{
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put(true, new ArrayList<Integer>());
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put(false, new ArrayList<Integer>());
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put(true, new ArrayList<>());
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put(false, new ArrayList<>());
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}},
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(acc, candidate) -> {
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acc.get(isPrime(acc.get(true), candidate))
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.add(candidate);
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},
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(acc, candidate) ->
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acc.get(isPrime(acc.get(true), candidate))
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.add(candidate)
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,
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(map1, map2) -> {
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map1.get(true).addAll(map2.get(true));
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map1.get(false).addAll(map2.get(false));

‎java8/src/main/java/com/brianway/learning/java8/streamapi/ToListCollector.java

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package com.brianway.learning.java8.streamapi;
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import static com.brianway.learning.java8.streamapi.Dish.menu;
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import static java.util.stream.Collector.Characteristics.CONCURRENT;
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import static java.util.stream.Collector.Characteristics.IDENTITY_FINISH;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.EnumSet;
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import java.util.List;
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import java.util.Set;
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import java.util.function.BiConsumer;
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import java.util.function.BinaryOperator;
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import java.util.function.Function;
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import java.util.function.Supplier;
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import java.util.stream.Collector;
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import java.util.stream.Collectors;
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/**
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* 自定义 ToListCollector
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*/
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public class ToListCollector<T> implements Collector<T, List<T>, List<T>> {
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@Override
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public Supplier<List<T>> supplier() {
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return () -> new ArrayList<T>();
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}
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@Override
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public BiConsumer<List<T>, T> accumulator() {
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return (list, item) -> list.add(item);
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}
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@Override
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public Function<List<T>, List<T>> finisher() {
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return i -> i;
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}
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@Override
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public BinaryOperator<List<T>> combiner() {
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return (list1, list2) -> {
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list1.addAll(list2);
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return list1;
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};
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}
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@Override
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public Set<Characteristics> characteristics() {
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return Collections.unmodifiableSet(EnumSet.of(IDENTITY_FINISH, CONCURRENT));
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}
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public static void main(String[] args) {
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List<Dish> dishes = menu.stream().collect(Collectors.toList());
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System.out.println(dishes);
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dishes = menu.stream().collect(new ToListCollector<>());
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System.out.println(dishes);
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dishes = menu.stream().collect(
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ArrayList::new,
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List::add,
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List::addAll);
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System.out.println(dishes);
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}
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}

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