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brianwaybrianway
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[add] add some stream api examples
1 parent dec2180 commit 874c3c4

8 files changed

Lines changed: 242 additions & 5 deletions

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‎java8/src/main/java/com/brianway/learning/java8/lambda/FilteringApples.java‎

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/**
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* Created by brian on 16/12/26.
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*
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*
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*/
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public class FilteringApples {
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public static void main(String[] args) {

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

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import java.util.stream.IntStream;
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import java.util.stream.Stream;
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/**
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* 斐波拉切数列的几种生成方法
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*/
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public class BuildingStreams {
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public static void main(String... args) throws Exception {
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.limit(5)
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.forEach(System.out::println);
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IntStream.generate(new IntSupplier() {
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public int getAsInt() {
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return 2;
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}
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}).limit(5)
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IntStream.generate(() -> 2)
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.limit(5)
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.forEach(System.out::println);
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IntSupplier fib = new IntSupplier() {

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

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import java.util.List;
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import java.util.Map;
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/**
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* 分别使用指令式和函数式进行分组
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*/
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public class GroupingTransactions {
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public static List<Transaction> transactions = Arrays.asList(

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

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package com.brianway.learning.java8.streamapi;
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import static java.util.stream.Collectors.toList;
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import java.util.Arrays;
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import java.util.List;
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/**
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* 流操作-中间操作
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*/
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public class Laziness {
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public static void main(String[] args) {
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List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8);
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List<Integer> twoEvenSquares =
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numbers.stream()
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.filter(n -> {
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System.out.println("filtering " + n); return n % 2 == 0;
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})
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.map(n -> {
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System.out.println("mapping " + n);
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return n * n;
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})
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.limit(2)
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.collect(toList());
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twoEvenSquares.stream().forEach(System.out::println);
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/streamapi/Mapping.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.Collectors.toList;
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import java.util.Arrays;
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import java.util.List;
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/**
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* 使用流-映射
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* 注意扁平映射
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*/
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public class Mapping {
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public static void main(String... args) {
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// map
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List<String> dishNames = menu.stream()
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.map(Dish::getName)
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.collect(toList());
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System.out.println(dishNames);
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// map
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List<String> words = Arrays.asList("Hello", "World");
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List<Integer> wordLengths = words.stream()
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.map(String::length)
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.collect(toList());
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System.out.println(wordLengths);
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// flatMap
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words.stream()
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.flatMap((String line) -> Arrays.stream(line.split("")))
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.distinct()
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.forEach(System.out::println);
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// flatMap
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List<Integer> numbers1 = Arrays.asList(1, 2, 3, 4, 5);
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List<Integer> numbers2 = Arrays.asList(6, 7, 8);
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List<int[]> pairs =
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numbers1.stream()
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.flatMap((Integer i) -> numbers2.stream()
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.map((Integer j) -> new int[] {i, j})
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)
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.filter(pair -> (pair[0] + pair[1]) % 3 == 0)
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.collect(toList());
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pairs.forEach(pair -> System.out.println("(" + pair[0] + ", " + pair[1] + ")"));
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}
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}

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

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package com.brianway.learning.java8.streamapi;
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import static java.util.stream.Collector.Characteristics.IDENTITY_FINISH;
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import static java.util.stream.Collectors.partitioningBy;
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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.HashMap;
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import java.util.List;
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import java.util.Map;
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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.Predicate;
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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.IntStream;
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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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*/
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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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}
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public static Map<Boolean, List<Integer>> partitionPrimes(int n) {
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return IntStream.rangeClosed(2, n).boxed()
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.collect(partitioningBy(PartitionPrimeNumbers::isPrime));
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}
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public static boolean isPrime(int candidate) {
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return IntStream.rangeClosed(2, candidate - 1)
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.limit((long) Math.floor(Math.sqrt((double) candidate)) - 1)
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.noneMatch(i -> candidate % i == 0);
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}
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public static Map<Boolean, List<Integer>> partitionPrimesWithCustomCollector(int n) {
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return IntStream.rangeClosed(2, n).boxed().collect(new PrimeNumbersCollector());
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}
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public static boolean isPrime(List<Integer> primes, Integer candidate) {
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double candidateRoot = Math.sqrt((double) candidate);
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//return primes.stream().filter(p -> p < candidateRoot).noneMatch(p -> candidate % p == 0);
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return takeWhile(primes, i -> i <= candidateRoot).stream().noneMatch(i -> candidate % i == 0);
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}
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public static <A> List<A> takeWhile(List<A> list, Predicate<A> p) {
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int i = 0;
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for (A item : list) {
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if (!p.test(item)) {
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return list.subList(0, i);
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}
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i++;
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}
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return list;
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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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}};
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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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.add(candidate);
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};
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}
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@Override
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public BinaryOperator<Map<Boolean, List<Integer>>> combiner() {
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return (Map<Boolean, List<Integer>> map1, Map<Boolean, List<Integer>> map2) -> {
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map1.get(true).addAll(map2.get(true));
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map1.get(false).addAll(map2.get(false));
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return map1;
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};
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}
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@Override
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public Function<Map<Boolean, List<Integer>>, Map<Boolean, List<Integer>>> finisher() {
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return i -> i;
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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));
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}
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}
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public 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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}},
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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));
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});
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/streamapi/Reducing.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.Collectors.reducing;
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public class Reducing {
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public static void main(String... args) {
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System.out.println("Total calories in menu: " + calculateTotalCalories());
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System.out.println("Total calories in menu: " + calculateTotalCaloriesWithMethodReference());
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System.out.println("Total calories in menu: " + calculateTotalCaloriesWithoutCollectors());
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System.out.println("Total calories in menu: " + calculateTotalCaloriesUsingSum());
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}
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private static int calculateTotalCalories() {
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return menu.stream().collect(reducing(0, Dish::getCalories, (Integer i, Integer j) -> i + j));
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}
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private static int calculateTotalCaloriesWithMethodReference() {
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return menu.stream().collect(reducing(0, Dish::getCalories, Integer::sum));
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}
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private static int calculateTotalCaloriesWithoutCollectors() {
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return menu.stream().map(Dish::getCalories).reduce(Integer::sum).get();
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}
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private static int calculateTotalCaloriesUsingSum() {
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return menu.stream().mapToInt(Dish::getCalories).sum();
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}
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}

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

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import java.util.Comparator;
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import java.util.List;
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/**
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* 指令式和函数式分别挑选低热量食物名
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*/
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public class StreamBasic {
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public static void main(String... args) {

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