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[add] add CompletableFuture examples in Java 8 module.
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‎java8/README.md‎

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@@ -64,3 +64,20 @@ Optional
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- OptionalMain: ptional 用法(map,flatMap,filter)
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- OptionalInAction: 使用 Optional 实战示例
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- ReadPositiveIntParam: 使用 Optional 示例
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CompletableFuture
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- v1/Shop: 商店类第一版,没有折扣
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- v1/ShopMain: 使用异步 API 的使用示例
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- v1/BestPriceFinder: 通过不同的方案实现价格查询:顺序流,并行流,CompletableFuture
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- v1/BestPriceFinderMain: 测试每种实现方案的执行时间
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- AsyncShop: 使用工厂方法 supplyAsync 创建 CompletableFuture
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- AsyncShopClient: 演示错误处理
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- ExchangeService: 货币兑换类
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- Discount: 折扣类
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- Quote: 解析商店返回的字符串
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- Shop: 商店类,报价按照 `name:price:code` 的格式
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- BestPriceFinder: 添加折扣后的版本
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- BestPriceFinderMain: 测试每种实现方案的执行时间
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‎java8/src/main/java/com/brianway/learning/java8/effective/async/AsyncShop.java‎

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package com.brianway.learning.java8.effective.async;
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import static com.brianway.learning.java8.effective.async.Util.delay;
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import static com.brianway.learning.java8.effective.async.Util.format;
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import java.util.Random;
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import java.util.concurrent.CompletableFuture;
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import java.util.concurrent.Future;
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/**
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* 使用工厂方法 supplyAsync 创建 CompletableFuture
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*/
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public class AsyncShop {
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private final String name;
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private final Random random;
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public AsyncShop(String name) {
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this.name = name;
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random = new Random(name.charAt(0) * name.charAt(1) * name.charAt(2));
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}
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public Future<Double> getPrice(String product) {
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/* // 抛出 CompletableFuture 内的异常
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CompletableFuture<Double> futurePrice = new CompletableFuture<>();
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new Thread( () -> {
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try {
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double price = calculatePrice(product);
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futurePrice.complete(price);
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} catch (Exception ex) {
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futurePrice.completeExceptionally(ex);
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}
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}).start();
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return futurePrice;
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*/
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// 使用工厂方法
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return CompletableFuture.supplyAsync(() -> calculatePrice(product));
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}
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private double calculatePrice(String product) {
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delay();
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if (true) {
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throw new RuntimeException("product not available");
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}
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return format(random.nextDouble() * product.charAt(0) + product.charAt(1));
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/AsyncShopClient.java‎

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package com.brianway.learning.java8.effective.async;
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import java.util.concurrent.Future;
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/**
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* 演示错误处理
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*/
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public class AsyncShopClient {
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public static void main(String[] args) {
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AsyncShop shop = new AsyncShop("BestShop");
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long start = System.nanoTime();
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Future<Double> futurePrice = shop.getPrice("myPhone");
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long incocationTime = ((System.nanoTime() - start) / 1_000_000);
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System.out.println("Invocation returned after " + incocationTime + " msecs");
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try {
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System.out.println("Price is " + futurePrice.get());
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} catch (Exception e) {
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throw new RuntimeException(e);
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}
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long retrivalTime = ((System.nanoTime() - start) / 1_000_000);
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System.out.println("Price returned after " + retrivalTime + " msecs");
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/BestPriceFinder.java‎

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package com.brianway.learning.java8.effective.async;
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import java.util.Arrays;
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import java.util.List;
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import java.util.concurrent.CompletableFuture;
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import java.util.concurrent.Executor;
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import java.util.concurrent.Executors;
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import java.util.concurrent.ThreadFactory;
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import java.util.stream.Collectors;
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import java.util.stream.Stream;
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/**
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* 添加折扣后的版本
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* 构造同步和异步操作
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*/
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public class BestPriceFinder {
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private final List<Shop> shops = Arrays.asList(new Shop("BestPrice"),
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new Shop("LetsSaveBig"),
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new Shop("MyFavoriteShop"),
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new Shop("BuyItAll"),
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new Shop("ShopEasy"));
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private final Executor executor = Executors.newFixedThreadPool(shops.size(), new ThreadFactory() {
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@Override
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public Thread newThread(Runnable r) {
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Thread t = new Thread(r);
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t.setDaemon(true);
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return t;
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}
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});
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public List<String> findPricesSequential(String product) {
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return shops.stream()
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.map(shop -> shop.getPrice(product))
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.map(Quote::parse)
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.map(Discount::applyDiscount)
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.collect(Collectors.toList());
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}
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public List<String> findPricesParallel(String product) {
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return shops.parallelStream()
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.map(shop -> shop.getPrice(product))
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.map(Quote::parse)
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.map(Discount::applyDiscount)
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.collect(Collectors.toList());
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}
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public List<String> findPricesFuture(String product) {
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List<CompletableFuture<String>> priceFutures = findPricesStream(product)
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.collect(Collectors.toList());
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return priceFutures.stream()
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.map(CompletableFuture::join)
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.collect(Collectors.toList());
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}
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/**
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* 分了三步:
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* 1. 获取价格
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* 2. 解析报价
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* 3. 为计算折扣价格构造 Future
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*/
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public Stream<CompletableFuture<String>> findPricesStream(String product) {
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return shops.stream()
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.map(shop -> CompletableFuture.supplyAsync(() -> shop.getPrice(product), executor))
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.map(future -> future.thenApply(Quote::parse))
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.map(future -> future.thenCompose(quote -> CompletableFuture.supplyAsync(
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() -> Discount.applyDiscount(quote), executor)));
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}
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/**
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* 响应 CompletableFuture 的 completion 事件
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* 把 Util 类中的 delay 调一下效果更明显
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*/
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public void printPricesStream(String product) {
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long start = System.nanoTime();
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CompletableFuture[] futures = findPricesStream(product)
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.map(f -> f.thenAccept(s -> System.out.println(s + " (done in " + ((System.nanoTime() - start) / 1_000_000) + " msecs)")))
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.toArray(CompletableFuture[]::new);
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CompletableFuture.allOf(futures).join();
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System.out.println("All shops have now responded in " + ((System.nanoTime() - start) / 1_000_000) + " msecs");
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/BestPriceFinderMain.java‎

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package com.brianway.learning.java8.effective.async;
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import java.util.List;
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import java.util.function.Supplier;
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/**
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* 测试每种实现方案的执行时间
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*/
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public class BestPriceFinderMain {
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private static BestPriceFinder bestPriceFinder = new BestPriceFinder();
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public static void main(String[] args) {
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execute("sequential", () -> bestPriceFinder.findPricesSequential("myPhone27S"));
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execute("parallel", () -> bestPriceFinder.findPricesParallel("myPhone27S"));
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execute("composed CompletableFuture", () -> bestPriceFinder.findPricesFuture("myPhone27S"));
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bestPriceFinder.printPricesStream("myPhone27S");
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}
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private static void execute(String msg, Supplier<List<String>> s) {
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long start = System.nanoTime();
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System.out.println(s.get());
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long duration = (System.nanoTime() - start) / 1_000_000;
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System.out.println(msg + " done in " + duration + " msecs");
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/Discount.java‎

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package com.brianway.learning.java8.effective.async;
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import static com.brianway.learning.java8.effective.async.Util.delay;
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import static com.brianway.learning.java8.effective.async.Util.format;
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/**
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* 折扣类
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*/
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public class Discount {
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public enum Code {
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NONE(0),
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SILVER(5),
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GOLD(10),
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PLATINUM(15),
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DIAMOND(20);
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private final int percentage;
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Code(int percentage) {
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this.percentage = percentage;
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}
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}
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public static String applyDiscount(Quote quote) {
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return quote.getShopName() + " price is " + Discount.apply(quote.getPrice(), quote.getDiscountCode());
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}
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private static double apply(double price, Code code) {
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delay();
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return format(price * (100 - code.percentage) / 100);
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/ExchangeService.java‎

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package com.brianway.learning.java8.effective.async;
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import static com.brianway.learning.java8.effective.async.Util.delay;
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/**
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* 货币兑换类
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*/
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public class ExchangeService {
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public enum Money {
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USD(1.0),
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EUR(1.35387),
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GBP(1.69715),
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CAD(.92106),
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MXN(.07683);
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private final double rate;
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Money(double rate) {
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this.rate = rate;
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}
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}
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public static double getRate(Money source, Money destination) {
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return getRateWithDelay(source, destination);
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}
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private static double getRateWithDelay(Money source, Money destination) {
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delay();
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return destination.rate / source.rate;
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/Quote.java‎

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package com.brianway.learning.java8.effective.async;
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/**
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* 解析商店返回的字符串
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*/
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public class Quote {
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private final String shopName;
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private final double price;
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private final Discount.Code discountCode;
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public Quote(String shopName, double price, Discount.Code discountCode) {
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this.shopName = shopName;
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this.price = price;
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this.discountCode = discountCode;
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}
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public static Quote parse(String s) {
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String[] split = s.split(":");
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String shopName = split[0];
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double price = Double.parseDouble(split[1]);
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Discount.Code discountCode = Discount.Code.valueOf(split[2]);
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return new Quote(shopName, price, discountCode);
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}
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public String getShopName() {
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return shopName;
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}
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public double getPrice() {
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return price;
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}
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public Discount.Code getDiscountCode() {
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return discountCode;
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}
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}

‎java8/src/main/java/com/brianway/learning/java8/effective/async/Shop.java‎

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package com.brianway.learning.java8.effective.async;
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import static com.brianway.learning.java8.effective.async.Util.delay;
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import static com.brianway.learning.java8.effective.async.Util.format;
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import java.util.Random;
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/**
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* 商店类
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* 报价按照 `name:price:code` 的格式
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*/
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public class Shop {
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private final String name;
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private final Random random;
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public Shop(String name) {
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this.name = name;
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random = new Random(name.charAt(0) * name.charAt(1) * name.charAt(2));
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}
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public String getPrice(String product) {
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double price = calculatePrice(product);
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Discount.Code code = Discount.Code.values()[random.nextInt(Discount.Code.values().length)];
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return name + ":" + price + ":" + code;
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}
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public double calculatePrice(String product) {
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delay();
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return format(random.nextDouble() * product.charAt(0) + product.charAt(1));
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}
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public String getName() {
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return name;
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}
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}

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