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‎src/main/java/lambdasinaction/chap10/Demo103.java‎

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package lambdasinaction.chap10;
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import java.util.Optional;
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import java.util.function.Consumer;
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/**
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* @author vector
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* @date: 2018/10/10 0010 11:29
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*/
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public class Demo103 {
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public static void main(String[] args) {
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Person person = new Person();
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Optional<Car> car = person.getCar();
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System.out.println(car.orElse(new Car()));
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car.ifPresent(System.out::println);
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;
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// Optional<Car> optCar2 = Optional.of(car)
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}
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}

‎src/main/java/lambdasinaction/chap10/Demo104.java‎

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package lambdasinaction.chap10;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Optional;
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/**
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* @author vector
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* @date: 2018/10/10 0010 14:00
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*/
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public class Demo104 {
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public static void main(String[] args) {
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Map<String, String> map = new HashMap<>();
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map.put("a", "sadfas");
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map.put("b", "sadfas1");
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map.put("c", "sadfas2");
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map.put("d", "sadfas3");
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String e = map.get("e");
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System.out.println(e);
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Optional<String> e1 = Optional.ofNullable(map.get("e"));
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String s = Optional.ofNullable(map.get("e")).orElse("unknown key");
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System.out.println(s);
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}
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public static Optional<Integer> stringToInt(String s) {
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try {
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return Optional.of(Integer.parseInt(s));
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} catch (NumberFormatException e) {
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return Optional.empty();
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}
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}
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}

‎src/main/java/lambdasinaction/chap10/OperationsWithOptional.java‎

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//package lambdasinaction.chap10;
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//
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//import java.util.*;
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//
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//import static java.util.Optional.of;
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//import static java.util.Optional.empty;
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//
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//public class OperationsWithOptional {
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//
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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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// Optional<Integer> opt1 = of(5);
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package lambdasinaction.chap10;
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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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Optional<Integer> opt1 = of(5);
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// Optional<Integer> opt2 = opt1.or(() -> of(4));
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//
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// System.out.println(
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// of(5).or(() -> of(4))
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// );
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// }
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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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}
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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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}

‎src/main/java/lambdasinaction/chap10/OptionalMain.java‎

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//package lambdasinaction.chap10;
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//
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//import java.util.*;
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//
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//import static java.util.stream.Collectors.toSet;
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//
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//public class OptionalMain {
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//
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// public String getCarInsuranceName(Optional<Person> person) {
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// return person.flatMap(Person::getCar)
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// .flatMap(Car::getInsurance)
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// .map(Insurance::getName)
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// .orElse("Unknown");
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// }
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//
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package lambdasinaction.chap10;
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import java.util.*;
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import static java.util.stream.Collectors.toSet;
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public class OptionalMain {
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public String getCarInsuranceName(Optional<Person> person) {
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return person.flatMap(Person::getCar)
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.flatMap(Car::getInsurance)
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.map(Insurance::getName)
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.orElse("Unknown");
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}
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// public Set<String> getCarInsuranceNames(List<Person> persons) {
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// return persons.stream()
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// .map(Person::getCar)
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// .flatMap(Optional::stream)
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// .collect(toSet());
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// }
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//}
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}

‎src/main/java/lambdasinaction/chap7/Demo71.java‎

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package lambdasinaction.chap7;
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import java.util.stream.Stream;
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/**
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* @author vector
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* @date: 2018/10/9 0009 11:21
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*/
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public class Demo71 {
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public static long sequentialSum(int n) {
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return Stream.iterate(1L, i -> i + 1).limit(n).reduce(0L, (l1, l2) -> l1 + l2);
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}
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public static long parallelSum(int n) {
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return Stream.iterate(1L, i -> i + 1).limit(n).parallel().reduce(0L, (l1, l2) -> l1 + l2);
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}
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public static long iterativeSum(int n) {
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long result = 0;
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for (int i = 0; i < n; i++) {
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result += i;
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}
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return result;
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}
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public static void main(String[] args) {
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}
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}

‎src/main/java/lambdasinaction/chap8/Peek.java‎

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public static void main(String[] args) {
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List<Integer> result = Stream.of(2, 3, 4, 5)
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List<Integer> result = Stream.of(2, 3, 4, 5, 13, 23)
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.peek(x -> System.out.println("taking from stream: " + x)).map(x -> x + 17)
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.peek(x -> System.out.println("after map: " + x)).filter(x -> x % 2 == 0)
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.peek(x -> System.out.println("after filter: " + x)).limit(3)

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