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Adding the source code examples for chapter 4 about Streams
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‎src/main/java/lambdasinaction/chap4/Dish.java‎

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package lambdasinaction.chap4;
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import java.util.*;
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public class Dish {
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private final String name;
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private final boolean vegetarian;
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private final int calories;
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private final Type type;
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public Dish(String name, boolean vegetarian, int calories, Type type) {
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this.name = name;
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this.vegetarian = vegetarian;
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this.calories = calories;
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this.type = type;
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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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public boolean isVegetarian() {
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return vegetarian;
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}
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public int getCalories() {
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return calories;
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}
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public Type getType() {
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return type;
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}
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public enum Type { MEAT, FISH, OTHER }
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@Override
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public String toString() {
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return name;
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}
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public static final List<Dish> menu =
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Arrays.asList( new Dish("pork", false, 800, Dish.Type.MEAT),
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new Dish("beef", false, 700, Dish.Type.MEAT),
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new Dish("chicken", false, 400, Dish.Type.MEAT),
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new Dish("french fries", true, 530, Dish.Type.OTHER),
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new Dish("rice", true, 350, Dish.Type.OTHER),
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new Dish("season fruit", true, 120, Dish.Type.OTHER),
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new Dish("pizza", true, 550, Dish.Type.OTHER),
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new Dish("prawns", false, 400, Dish.Type.FISH),
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new Dish("salmon", false, 450, Dish.Type.FISH));
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}

‎src/main/java/lambdasinaction/chap4/Filtering.java‎

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package lambdasinaction.chap4;
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import java.util.stream.*;
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import java.util.*;
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import static lambdasinaction.chap4.Dish.menu;
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public class Filtering{
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public static void main(String...args){
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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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numbers.stream().limit(20).forEach(System.out::println);
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}
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}

‎src/main/java/lambdasinaction/chap4/Finding.java‎

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package lambdasinaction.chap4;
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import java.util.stream.*;
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import java.util.*;
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import static lambdasinaction.chap4.Dish.menu;
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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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}

‎src/main/java/lambdasinaction/chap4/Mapping.java‎

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package lambdasinaction.chap4;
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import java.util.stream.*;
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import java.util.*;
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import static java.util.stream.Collectors.toList;
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import static lambdasinaction.chap4.Dish.menu;
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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(i -> numbers2.stream()
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.map(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(e -> System.out.println("(" + e[0] + ", " + e[1] + ")"));
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}
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}

‎src/main/java/lambdasinaction/chap4/PuttingIntoPractice.java‎

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package lambdasinaction.chap4;
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import java.util.*;
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import java.util.stream.*;
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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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public class PuttingIntoPractice{
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public static void main(String ...args){
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Trader raoul = new Trader("Raoul", "Cambridge");
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Trader mario = new Trader("Mario","Milan");
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Trader alan = new Trader("Alan","Cambridge");
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Trader brian = new Trader("Brian","Cambridge");
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List<Transaction> transactions = Arrays.asList(
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new Transaction(brian, 2011, 300),
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new Transaction(raoul, 2012, 1000),
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new Transaction(raoul, 2011, 400),
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new Transaction(mario, 2012, 710),
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new Transaction(mario, 2012, 700),
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new Transaction(alan, 2012, 950)
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);
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// Query 1: Find all transactions from year 2011 and sort them by value (small to high).
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List<Transaction> tr2011 = transactions.stream()
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.filter(transaction -> transaction.getYear() == 2011)
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.sorted(comparing(Transaction::getValue))
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.collect(toList());
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System.out.println(tr2011);
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// Query 2: What are all the unique cities where the traders work?
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List<String> cities =
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transactions.stream()
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.map(transaction -> transaction.getTrader().getCity())
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.distinct()
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.collect(toList());
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System.out.println(cities);
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// Query 3: Find all traders from Cambridge and sort them by name.
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List<Trader> traders =
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transactions.stream()
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.map(Transaction::getTrader)
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.filter(trader -> trader.getCity().equals("Cambridge"))
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.distinct()
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.sorted(comparing(Trader::getName))
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.collect(toList());
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System.out.println(traders);
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// Query 4: Return a string of all traders’ names sorted alphabetically.
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String traderStr =
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transactions.stream()
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.map(transaction -> transaction.getTrader().getName())
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.distinct()
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.sorted()
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.reduce("", (n1, n2) -> n1 + n2);
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System.out.println(traderStr);
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// Query 5: Are there any trader based in Milan?
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boolean milanBased =
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transactions.stream()
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.anyMatch(transaction -> transaction.getTrader()
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.getCity()
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.equals("Milan")
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);
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System.out.println(milanBased);
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// Query 6: Update all transactions so that the traders from Milan are set to Cambridge.
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transactions.stream()
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.map(Transaction::getTrader)
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.filter(trader -> trader.getCity().equals("Milan"))
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.forEach(trader -> trader.setCity("Cambridge"));
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System.out.println(transactions);
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// Query 7: What's the highest value in all the transactions?
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int highestValue =
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transactions.stream()
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.map(Transaction::getValue)
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.reduce(0, Integer::max);
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System.out.println(highestValue);
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}
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}

‎src/main/java/lambdasinaction/chap4/Reducing.java‎

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package lambdasinaction.chap4;
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import java.util.stream.*;
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import java.util.*;
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import static lambdasinaction.chap4.Dish.menu;
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public class Reducing{
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public static void main(String...args){
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List<Integer> numbers = Arrays.asList(3,4,5,1,2);
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int sum = numbers.stream().reduce(0, (a, b) -> a + b);
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System.out.println(sum);
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int sum2 = numbers.stream().reduce(0, Integer::sum);
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System.out.println(sum2);
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int max = numbers.stream().reduce(0, (a, b) -> Integer.max(a, b));
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System.out.println(max);
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}
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}

‎src/main/java/lambdasinaction/chap4/StreamBasic.java‎

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package lambdasinaction.chap4;
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import java.util.*;
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import java.util.stream.*;
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import static java.util.stream.Collectors.toList;
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import lambdasinaction.chap5.Dish;
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import static lambdasinaction.chap5.Dish.menu;
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public class StreamBasic {
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public static void main(String...args){
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List<String> names = menu.stream()
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.filter(d -> d.getCalories() > 300)
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.map(Dish::getName)
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.limit(3)
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.collect(toList());
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System.out.println(names);
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}
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}

‎src/main/java/lambdasinaction/chap4/StreamVsCollection.java‎

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package lambdasinaction.chap4;
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import java.util.*;
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import java.util.stream.*;
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import static java.util.stream.Collectors.toList;
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public class StreamVsCollection {
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public static void main(String...args){
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List<String> names = Arrays.asList("Java8", "Lambdas", "In", "Action");
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Stream<String> s = names.stream();
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s.forEach(System.out::println);
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s.forEach(System.out::println); // Exception
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}
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}

‎src/main/java/lambdasinaction/chap4/Trader.java‎

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package lambdasinaction.chap4;
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public class Trader{
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private String name;
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private String city;
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public Trader(String n, String c){
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this.name = n;
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this.city = c;
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}
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public String getName(){
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return this.name;
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}
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public String getCity(){
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return this.city;
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}
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public void setCity(String newCity){
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this.city = newCity;
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}
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public String toString(){
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return "Trader:"+this.name + " in " + this.city;
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}
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}

‎src/main/java/lambdasinaction/chap4/Transaction.java‎

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package lambdasinaction.chap4;
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public class Transaction{
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private Trader trader;
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private int year;
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private int value;
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public Transaction(Trader trader, int year, int value)
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{
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this.trader = trader;
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this.year = year;
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this.value = value;
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}
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public Trader getTrader(){
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return this.trader;
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}
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public int getYear(){
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return this.year;
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}
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public int getValue(){
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return this.value;
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}
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public String toString(){
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return "{" + this.trader + ", " +
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"year: "+this.year+", " +
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"value:" + this.value +"}";
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}
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}

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