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[add] add usage examples of Stream API. · JavaDevelopRep/java-learning@b5aac3e · GitHub

/ java-learning Public
forked from brianway/java-learning

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[add] add usage examples of Stream API.
1 parent 519ba7a commit b5aac3e

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‎java-jvm/src/main/java/com/brianway/learning/java/jvm/dynamictype/GrandFatherCaller.java‎

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* Created by brian on 17/3/20.
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* 使用 MethodHandle 来访问祖类方法
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* TODO 为什么打印出来的是 "i am father" 而不是 "i am grandfather"?
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* 参考:
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* https://www.zhihu.com/question/57379777
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* https://www.zhihu.com/question/40427344/answer/86545388
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*/
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public class GrandFatherCaller {
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class GrandFather {

‎java8/README.md‎

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## steam API
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- Dish:
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- Dish: 菜肴类,有一个静态属性的菜肴列表
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- StreamBasic: 指令式和函数式分别挑选低热量食物名
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- StreamOperation: 流操作:中间操作和终端操作
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- StreamOperation: 流操作(中间操作和终端操作)
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使用流
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- Filtering: 筛选(谓词筛选：filter;筛选互异的元素：distinct;忽略头几个元素：limit;截短至指定长度：skip)
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- Mapping: 映射
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- PuttingIntoPractice: 各种流操作的使用示例

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

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}
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/**
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* 指令式
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*/
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public static List<String> getLowCaloricDishesNamesInJava7(List<Dish> dishes) {
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List<Dish> lowCaloricDishes = new ArrayList<>();
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for (Dish d : dishes) {
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return lowCaloricDishesName;
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}
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/**
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* 函数式
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*/
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public static List<String> getLowCaloricDishesNamesInJava8(List<Dish> dishes) {
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return dishes.stream()
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.filter(d -> d.getCalories() < 400)

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

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.limit(3)
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.collect(Collectors.toList());
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System.out.println(names);
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//forEach 是一个返回 void 的终端操作
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System.out.println("------forEach-------");
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menu.stream().forEach(System.out::println);
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}
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}

java8/src/main/java/com/brianway/learning/java8/streamapi/PuttingIntoPractice.java renamed to java8/src/main/java/com/brianway/learning/java8/streamapi/practice/PuttingIntoPractice.java

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package com.brianway.learning.java8.streamapi;
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package com.brianway.learning.java8.streamapi.practice;
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import static java.util.Comparator.comparing;
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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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* 各种流操作的使用示例
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*/
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public class PuttingIntoPractice {
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public static void main(String... args) {
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Trader raoul = new Trader("Raoul", "Cambridge");

java8/src/main/java/com/brianway/learning/java8/streamapi/Trader.java renamed to java8/src/main/java/com/brianway/learning/java8/streamapi/practice/Trader.java

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package com.brianway.learning.java8.streamapi;
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package com.brianway.learning.java8.streamapi.practice;
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public class Trader {
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java8/src/main/java/com/brianway/learning/java8/streamapi/Transaction.java renamed to java8/src/main/java/com/brianway/learning/java8/streamapi/practice/Transaction.java

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package com.brianway.learning.java8.streamapi;
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package com.brianway.learning.java8.streamapi.practice;
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public class Transaction {
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‎java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Filtering.java‎

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package com.brianway.learning.java8.streamapi.usage;
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import com.brianway.learning.java8.streamapi.Dish;
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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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*筛选
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* - 谓词筛选：filter
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* - 筛选互异的元素：distinct
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* - 忽略头几个元素：limit
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* - 截短至指定长度：skip
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*/
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public class Filtering {
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public static void main(String...args){
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// Filtering with predicate
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List<Dish> vegetarianMenu =
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menu.stream()
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.filter(Dish::isVegetarian)
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.collect(toList());
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vegetarianMenu.forEach(System.out::println);
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// Filtering unique elements
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List<Integer> numbers = Arrays.asList(1, 2, 1, 3, 3, 2, 4);
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numbers.stream()
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.filter(i -> i % 2 == 0)
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.distinct()
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.forEach(System.out::println);
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// Truncating a stream
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List<Dish> dishesLimit3 =
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menu.stream()
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.filter(d -> d.getCalories() > 300)
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.limit(3)
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.collect(toList());
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dishesLimit3.forEach(System.out::println);
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// Skipping elements
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List<Dish> dishesSkip2 =
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menu.stream()
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.filter(d -> d.getCalories() > 300)
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.skip(2)
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.collect(toList());
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dishesSkip2.forEach(System.out::println);
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Finding.java‎

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package com.brianway.learning.java8.streamapi.usage;
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import com.brianway.learning.java8.streamapi.Dish;
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import static com.brianway.learning.java8.streamapi.Dish.menu;
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import java.util.Optional;
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/**
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* 查找和匹配
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*/
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public class Finding {
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public static void main(String...args){
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if(isVegetarianFriendlyMenu()){
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System.out.println("Vegetarian friendly");
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}
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System.out.println(isHealthyMenu());
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System.out.println(isHealthyMenu2());
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Optional<Dish> dish = findVegetarianDish();
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dish.ifPresent(d -> System.out.println(d.getName()));
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}
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private static boolean isVegetarianFriendlyMenu(){
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return menu.stream().anyMatch(Dish::isVegetarian);
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}
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private static boolean isHealthyMenu(){
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return menu.stream().allMatch(d -> d.getCalories() < 1000);
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}
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private static boolean isHealthyMenu2(){
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return menu.stream().noneMatch(d -> d.getCalories() >= 1000);
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}
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private static Optional<Dish> findVegetarianDish(){
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return menu.stream().filter(Dish::isVegetarian).findAny();
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}
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}

java8/src/main/java/com/brianway/learning/java8/streamapi/Mapping.java renamed to java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Mapping.java

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package com.brianway.learning.java8.streamapi;
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package com.brianway.learning.java8.streamapi.usage;
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import com.brianway.learning.java8.streamapi.Dish;
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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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/**
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* 使用流-映射
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* 注意扁平映射
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* flatMap 的效果:各个数组不是分别映射成一个流,而是映射成 流的内容
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*/
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public class Mapping {
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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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// flatMap
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List<int[]> pairs2 = numbers1.stream()
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.flatMap(i -> numbers2.stream()
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.filter(j -> (i + j) % 3 == 0)
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.map(j -> new int[] {i, j})
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)
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.collect(toList());
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System.out.println("----------");
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pairs2.forEach(pair -> System.out.println("(" + pair[0] + ", " + pair[1] + ")"));
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}
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}

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