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mariofuscomariofusco
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CompletableFuture examples
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‎src/main/java/lambdasinaction/chap10/AsyncShop.java

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package lambdasinaction.chap10;
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import java.text.*;
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import java.util.*;
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import java.util.concurrent.*;
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import static lambdasinaction.chap10.Util.*;
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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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/*
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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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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) throw new RuntimeException("product not available");
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return format(random.nextDouble() * product.charAt(0) + product.charAt(1));
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}
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}

‎src/main/java/lambdasinaction/chap10/AsyncShopClient.java

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package lambdasinaction.chap10;
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import java.util.concurrent.*;
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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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}

‎src/main/java/lambdasinaction/chap10/BestPriceFinder.java

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package lambdasinaction.chap10;
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import java.util.*;
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import java.util.concurrent.*;
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import java.util.stream.*;
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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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/*
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public List<String> findPriceSequential(String product) {
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return shops.stream()
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.map(shop -> shop.getName() + " price is " + shop.calculatePrice(product))
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.collect(Collectors.<String>toList());
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}
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public List<String> findPriceParallel(String product) {
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return shops.parallelStream()
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.map(shop -> shop.getName() + " price is " + shop.calculatePrice(product))
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.collect(Collectors.<String>toList());
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}
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public List<String> findPrice(String product) {
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List<CompletableFuture<String>> priceFutures =
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shops.stream()
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.map(shop -> CompletableFuture.supplyAsync(() -> shop.getName() + " price is " + shop.calculatePrice(product)))
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.collect(Collectors.<CompletableFuture<String>>toList());
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List<String> prices = priceFutures.stream()
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.map(CompletableFuture::join)
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.collect(Collectors.<String>toList());
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return prices;
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//return sequence(priceFutures).join();
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}
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/*/
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public List<String> findPriceSequential(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.<String>toList());
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}
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public List<String> findPriceParallel(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.<String>toList());
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}
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public List<String> findPrice(String product) {
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List<CompletableFuture<String>> priceFutures = findPriceStream(product)
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.collect(Collectors.<CompletableFuture<String>>toList());
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return priceFutures.stream()
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.map(CompletableFuture::join)
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.collect(Collectors.<String>toList());
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}
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public Stream<CompletableFuture<String>> findPriceStream(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(() -> Discount.applyDiscount(quote), executor)));
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}
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}

‎src/main/java/lambdasinaction/chap10/BestPriceFinderMain.java

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package lambdasinaction.chap10;
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import java.util.*;
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import java.util.concurrent.*;
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import java.util.function.*;
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import static java.util.stream.Collectors.toList;
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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.findPriceSequential("myPhone"));
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//execute("parallel", () -> bestPriceFinder.findPriceParallel("myPhone"));
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//execute("composed CompletableFuture", () -> bestPriceFinder.findPrice("myPhone"));
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printPricesStream();
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}
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private static void printPricesStream() {
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long start = System.nanoTime();
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List<CompletableFuture<Void>> futures =
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bestPriceFinder.findPriceStream("myPhone")
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.map(f -> f.thenAccept(s -> System.out.println(s + " (find in " + ((System.nanoTime() - start) / 1_000_000) + " msecs)")))
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.collect(toList());
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CompletableFuture.allOf(futures.toArray(new CompletableFuture[futures.size()])).join();
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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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}

‎src/main/java/lambdasinaction/chap10/Discount.java

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package lambdasinaction.chap10;
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import java.util.*;
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import static lambdasinaction.chap10.Util.*;
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public class Discount {
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public enum Code {
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NONE(0), SILVER(5), GOLD(10), PLATINUM(15), 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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}

‎src/main/java/lambdasinaction/chap10/Quote.java

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package lambdasinaction.chap10;
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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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}

‎src/main/java/lambdasinaction/chap10/Shop.java

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package lambdasinaction.chap10;
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import java.util.*;
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import static lambdasinaction.chap10.Util.*;
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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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}

‎src/main/java/lambdasinaction/chap10/Util.java

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package lambdasinaction.chap10;
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import java.text.*;
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import java.util.*;
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import java.util.concurrent.*;
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import java.util.stream.*;
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public class Util {
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private static final Random RANDOM = new Random(0);
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private static final DecimalFormat formatter = new DecimalFormat("#.##", new DecimalFormatSymbols(Locale.US));
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public static void delay() {
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//int delay = 1000;
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int delay = 500 + RANDOM.nextInt(2000);
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try {
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Thread.sleep(delay);
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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public static double format(double number) {
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synchronized (formatter) {
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return new Double(formatter.format(number));
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}
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}
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public static <T> CompletableFuture<List<T>> sequence(List<CompletableFuture<T>> futures) {
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/*
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CompletableFuture<Void> allDoneFuture =
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CompletableFuture.allOf(futures.toArray(new CompletableFuture[futures.size()]));
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return allDoneFuture.thenApply(v ->
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futures.stream().
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map(future -> future.join()).
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collect(Collectors.<T>toList())
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);
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*/
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return CompletableFuture.supplyAsync(() -> futures.stream().
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map(future -> future.join()).
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collect(Collectors.<T>toList()));
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}
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}

‎src/main/java/lambdasinaction/chap9/OperationsWithOptional.java

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package lambdasinaction.chap9;
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import java.util.*;
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import static java.util.Optional.of;
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import static java.util.Optional.empty;
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public class OperationsWithOptional {
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public static void main(String... args) {
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System.out.println(max(of(3), of(5)));
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System.out.println(max(empty(), of(5)));
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}
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public static final Optional<Integer> max(Optional<Integer> i, Optional<Integer> j) {
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return i.flatMap(a -> j.map(b -> Math.max(a, b)));
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}
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}

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