(Integer i) -> return "hello"+i;   //错误的Lambda，return是一个控制流语句，需要{}
(String s) -> {"hello";}       //“hello”是一个表达式，不是语句，不需要{}，可以写成{return “hello”;}

List<String> list = new ArrayList<>();

import java.util.List;
import java.util.ArrayList;
import java.time.chrono.IsoChronology;
import java.time.LocalDate;

public class Person {

    public enum Sex {
        MALE, FEMALE
    }

    String name;
    LocalDate birthday;
    Sex gender;
    String emailAddress;

    Person(String nameArg, LocalDate birthdayArg,
           Sex genderArg, String emailArg) {
        name = nameArg;
        birthday = birthdayArg;
        gender = genderArg;
        emailAddress = emailArg;
    }

    public int getAge() {
        return birthday
                .until(IsoChronology.INSTANCE.dateNow())
                .getYears();
    }

    public void printPerson() {
        System.out.println(name + ", " + this.getAge());
    }

    public Sex getGender() {
        return gender;
    }

    public String getName() {
        return name;
    }

    public String getEmailAddress() {
        return emailAddress;
    }

    public LocalDate getBirthday() {
        return birthday;
    }

    public static int compareByAge(Person a, Person b) {
        return a.birthday.compareTo(b.birthday);
    }

    public static List<Person> createRoster() {

        List<Person> roster = new ArrayList<>();
        roster.add(
                new Person(
                        "Fred",
                        IsoChronology.INSTANCE.date(1980, 6, 20),
                        Person.Sex.MALE,
                        "fred@example.com"));
        roster.add(
                new Person(
                        "Jane",
                        IsoChronology.INSTANCE.date(1990, 7, 15),
                        Person.Sex.FEMALE, "jane@example.com"));
        roster.add(
                new Person(
                        "George",
                        IsoChronology.INSTANCE.date(1991, 8, 13),
                        Person.Sex.MALE, "george@example.com"));
        roster.add(
                new Person(
                        "Bob",
                        IsoChronology.INSTANCE.date(2000, 9, 12),
                        Person.Sex.MALE, "bob@example.com"));

        return roster;
    }
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;

public class RosterTest {

    interface CheckPerson {
        boolean test(Person p);
    }

    /**
     * 1. eg：输出年龄大于20岁的成员
     *   匹配符合某一特征的成员的方法
     *   如果老板要年龄在某一区间的成员呢？接着换方法
     */
    public static void printPersonsOlderThan(List<Person> roster, int age) {
        for (Person p : roster) {
            if (p.getAge() >= age) {
                p.printPerson();
            }
        }
    }

    /**
     * 2. eg:输出年龄在14到30岁之间的成员
     * 		更全面的匹配方法
     * 		如果老板只要男性成员呢？
     */
    public static void printPersonsWithinAgeRange(
            List<Person> roster, int low, int high) {
        for (Person p : roster) {
            if (low <= p.getAge() && p.getAge() < high) {
                p.printPerson();
            }
        }
    }

    /**
     * 3. eg:老板又提出了各种复杂的需求，不要处女座的、只要邮箱是163的，怎么搞？
     * 方法1：在本地类中指定搜索条件代码，通过接口方式，不同的需求对应不同的实现类，
     *		 每次都要新建实现类，写大量的代码
     * 方法2：在匿名类中指定搜索条件代码，不需要写各种实现，但是还要写个interface CheckPerson，
     *       而且匿名类写起来也挺麻烦
     * 方法3：Lambda表达式是懒人的不二之选，CheckPerson是一个只包含一个抽象方法的接口，
     *	     比较简单，Lambda可以省略其实现
     */
    public static void printPersons(
            List<Person> roster, CheckPerson tester) {
        for (Person p : roster) {
            if (tester.test(p)) {
                p.printPerson();
            }
        }
    }

    /**
     * 4. eg: 搞这么久，还得写一个接口，而且是只有一个抽象方法，还是不爽？
     * 			你也可以使用标准的函数接口来代替接口CheckPerson，从而进一步减少所需的代码量
     * 			java.util.function包中定义了标准的函数接口
     * 			我们可以使用JDK8提供的 Predicate<T>接口来代替CheckPerson。
     *			该接口包含方法boolean test(T t)
     */
    public static void printPersonsWithPredicate(
            List<Person> roster, Predicate<Person> tester) {
        for (Person p : roster) {
            if (tester.test(p)) {
                p.printPerson();
            }
        }
    }

    /**
     * 5. Lambda表达式可不只是能够简化匿名类
     * 		简化 p.printPerson(), 
     * 		使用Consumer<T>接口的void accept(T t)方法，相当于入参的操作
     */
    public static void processPersons(
            List<Person> roster,
            Predicate<Person> tester,
            Consumer<Person> block) {
        for (Person p : roster) {
            if (tester.test(p)) {
                block.accept(p);
            }
        }
    }

    /**
     * 6. eg: 老板说了只想看到邮箱
     * Function<T,R>接口，相当于输入类型，mapper定义参数，block负责方对给定的参数进行执行
     */
    public static void processPersonsWithFunction(
            List<Person> roster,
            Predicate<Person> tester,
            Function<Person, String> mapper,
            Consumer<String> block) {
        for (Person p : roster) {
            if (tester.test(p)) {
                String data = mapper.apply(p);
                block.accept(data);
            }
        }
    }

    // 7. 使用泛型
    public static <X, Y> void processElements(
            Iterable<X> source,
            Predicate<X> tester,
            Function<X, Y> mapper,
            Consumer<Y> block) {
        for (X p : source) {
            if (tester.test(p)) {
                Y data = mapper.apply(p);
                block.accept(data);
            }
        }
    }

    public static void main(String[] args) {
        List<Person> roster = Person.createRoster();

        /**
         * 1. 输出年龄大于20岁的成员
         */
        System.out.println("Persons older than 20:");
        printPersonsOlderThan(roster, 20);
        System.out.println();

        /**
         * 2. 输出年龄在14到30岁之间的成员
         */
        System.out.println("Persons between the ages of 14 and 30:");
        printPersonsWithinAgeRange(roster, 14, 30);
        System.out.println();

        /**
         * 3. 输出年龄在18到25岁的男性成员
         * （在本地类中指定搜索条件）
         *   您可以使用一个匿名类而不是一个本地类，并且不必为每个搜索声明一个新类
         */
        System.out.println("Persons who are eligible for Selective Service:");
        class CheckPersonEligibleForSelectiveService implements CheckPerson {
            public boolean test(Person p) {
                return p.getGender() == Person.Sex.MALE
                        && p.getAge() >= 18
                        && p.getAge() <= 25;
            }
        }

        // 这个其实就是通过行为参数化传递代码
        printPersons(
                roster, new CheckPersonEligibleForSelectiveService());

        System.out.println();

        // 3. 在匿名类中指定搜索条件代码
        System.out.println("Persons who are eligible for Selective Service " +
                "(anonymous class):");
        printPersons(
                roster,
                new CheckPerson() {
                    public boolean test(Person p) {
                        return p.getGender() == Person.Sex.MALE
                                && p.getAge() >= 18
                                && p.getAge() <= 25;
                    }
                }
        );

        System.out.println();

        // 3: 使用Lambda表达式简化代码，一个箭头
        System.out.println("Persons who are eligible for Selective Service " +
                "(lambda expression):");

        printPersons(
                roster,
                (Person p) -> p.getGender() == Person.Sex.MALE
                        && p.getAge() >= 18
                        && p.getAge() <= 25
        );

        System.out.println();

        // 4. 使用Lambda的标准功能接口
        System.out.println("Persons who are eligible for Selective Service " +
                "(with Predicate parameter):");

        printPersonsWithPredicate(
                roster,
                p -> p.getGender() == Person.Sex.MALE
                        && p.getAge() >= 18
                        && p.getAge() <= 25
        );

        System.out.println();

        //5.使用Predicate和Consumer参数
        System.out.println("5. Persons who are eligible for Selective Service " +
                "(with Predicate and Consumer parameters):");

        processPersons(
                roster,
                p -> p.getGender() == Person.Sex.MALE
                        && p.getAge() >= 18
                        && p.getAge() <= 25,
                p -> p.printPerson()
        );

        System.out.println();

        // 6. 通过Function<T,R> 指定输出类型
        System.out.println("Persons who are eligible for Selective Service " +
                "(with Predicate, Function, and Consumer parameters):");

        processPersonsWithFunction(
                roster,
                p -> p.getGender() == Person.Sex.MALE
                        && p.getAge() >= 18
                        && p.getAge() <= 25,
                p -> p.getEmailAddress(),
                email -> System.out.println(email)
        );

        System.out.println();

        // 7. 使用泛型
        System.out.println("Persons who are eligible for Selective Service " +
                "(generic version):");

        processElements(
                roster,
                p -> p.getGender() == Person.Sex.MALE
                        && p.getAge() >= 18
                        && p.getAge() <= 25,
                p -> p.getEmailAddress(),
                email -> System.out.println(email)
        );

        System.out.println();

        // 8: 使用接受Lambda表达式的批量数据操作
        System.out.println("Persons who are eligible for Selective Service " +
                "(with bulk data operations):");

        roster.stream()
                .filter(
                        p -> p.getGender() == Person.Sex.MALE
                                && p.getAge() >= 18
                                && p.getAge() <= 25)
                .map(p -> p.getEmailAddress())
                .forEach(email -> System.out.println(email));
        System.out.println();

        /**
         *  9. 按年龄排序。Java 8 之前需要实现 Comparator 接口
         *  接口比较器是一个功能接口。因此，
         *  可以使用lambda表达式来代替定义并创建一个实现了Comparator的类的新实例:
         */
        Person[] rosterAsArray = roster.toArray(new Person[roster.size()]);

        Arrays.sort(rosterAsArray,
                (a, b) -> Person.compareByAge(a, b)
        );

        for (Person person : roster) {
            person.printPerson();
        }

        /**
         *  这种比较两个Person实例的出生日期的方法已经作为Person. 
         *	comparebyage存在。你可以在lambda表达式中调用这个方法
         */

        Arrays.sort(rosterAsArray,
                (a, b) -> Person.compareByAge(a, b)
        );

        /**
         *  ===================================================================
         *  方法引用：
         * 这个lambda表达式调用现有的方法，所以您可以使用方法引用而不是lambda表达式
         *  Person::compareByAge 等同于 (a, b) -> Person.compareByAge(a, b)
         */
        Arrays.sort(rosterAsArray, Person::compareByAge);

        System.out.println();

        // Reference to an Instance Method of a Particular Object
        class ComparisonProvider {
            public int compareByName(Person a, Person b) {
                return a.getName().compareTo(b.getName());
            }

            public int compareByAge(Person a, Person b) {
                return a.getBirthday().compareTo(b.getBirthday());
            }
        }
        ComparisonProvider myComparisonProvider = new ComparisonProvider();
        Arrays.sort(rosterAsArray, myComparisonProvider::compareByName);
        for (Person person : rosterAsArray) {
            person.printPerson();
        }

        System.out.println();

        /**
         * 引用特定类型的任意对象的实例方法
         * String::compareToIgnoreCase 格式化 (String a, String b) ，
         *  并去调用 a.compareToIgnoreCase(b)
         */
        String[] stringArray = { "Barbara", "James", "Mary", "John",
                "Patricia", "Robert", "Michael", "Linda" };
        Arrays.sort(stringArray, String::compareToIgnoreCase);
        for (String s : stringArray) {
            System.out.println(s);
        }


        System.out.println();

        // 通过 stream 将计算集合的和
        Integer[] intArray = {1, 2, 3, 4, 5, 6, 7, 8 };
        List<Integer> listOfIntegers =
                new ArrayList<>(Arrays.asList(intArray));
        System.out.println("Sum of integers: " +
                listOfIntegers
                        .stream()
                        .reduce(Integer::sum).get());
    }
}

@FunctionalInterface    //@FunctionalInterface标注该接口会被设计成一个函数式接口，否则会编译错误
public interface MyFunc<T> {
    T getValue(T t);
}

public static String toUpperString(MyFunc<String> myFunc, String str) {
    return myFunc.getValue(str);
}

public static void main(String[] args) {
    String newStr = toUpperString((str) -> str.toUpperCase(), "abc");
    System.out.println(newStr);
}

import org.junit.Test;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;

/*
 * Java8 内置的四大核心函数式接口
 * Consumer<T> : 消费型接口  void accept(T t);
 * 		
 * Supplier<T> : 供给型接口   T get();
 *
 * Function<T, R> : 函数型接口  R apply(T t);
 *
 * Predicate<T> : 断言型接口   boolean test(T t);
 */
public class FunctionalInterfaceTest {

    //Predicate<T> 断言型接口：将满足条件的字符串放入集合
    public List<String> filterStr(List<String> list, Predicate<String> predicate) {
        List<String> newList = new ArrayList<>();
        for (String s : list) {
            if (predicate.test(s)) {
                newList.add(s);
            }
        }
        return newList;
    }

    @Test
    public void testPredicate() {
        List<String> list = Arrays.asList("hello", "java8", "function", "predicate");
        List<String> newList = filterStr(list, s -> s.length() > 5);
        for (String s : newList) {
            System.out.println(s);
        }
    }

    // Function<T, R> 函数型接口：处理字符串
    public String strHandler(String str, Function<String, String> function) {
        return function.apply(str);
    }

    @Test
    public void testFunction() {
        String str1 = strHandler("测试内置函数式接口", s -> s.substring(2));
        System.out.println(str1);

        String str2 = strHandler("abcdefg", s -> s.toUpperCase());
        System.out.println(str2);
    }

    //Supplier<T> 供给型接口 :产生指定个数的整数，并放入集合
    public List<Integer> getNumList(int num, Supplier<Integer> supplier) {
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < num; i++) {
            Integer n = supplier.get();
            list.add(n);
        }
        return list;
    }

    @Test
    public void testSupplier() {
        List<Integer> numList = getNumList(10, () -> (int) (Math.random() * 100));

        for (Integer num : numList) {
            System.out.println(num);
        }
    }

    //Consumer<T> 消费型接口 :修改参数
    public void modifyValue(Integer value, Consumer<Integer> consumer) {
        consumer.accept(value);
    }

    @Test
    public void testConsumer() {
        modifyValue(3, s -> System.out.println(s * 3));
    }
}

List<Integer> list = new ArrayList();
	for (int i = 0; i < 10; i++) {
	list.add(i);    //int被装箱为Integer
}

BinaryOperator<Double> binaryOperator = (x,y)->Math.pow(x,y);
//等价于
BinaryOperator<Double> binaryOperator1 = Math::pow;

Arrays.sort(rosterAsArray, Person::compareByAge);
//---------------------
@Test
public void test3(){
    BiFunction<Double,Double,Double> bif = (x,y)->Math.max(x,y);
    System.out.println(bif.apply(22.1,23.2));

    System.out.println("===等价于===");

    BiFunction<Double,Double,Double> bif1 = Math::max;
    System.out.println(bif1.apply(22.1,23.2));
}

@Test
public void test4(){
    Comparator<Integer> com = (x, y)->Integer.compare(x,y);
    System.out.println(com.compare(1,2));

    System.out.println("===等价于===");
    Comparator<Integer> com1 = Integer::compare;
    System.out.println(com1.compare(1,2));
}

class ComparisonProvider {
    public int compareByName(Person a, Person b) {
        return a.getName().compareTo(b.getName());
    }
        
    public int compareByAge(Person a, Person b) {
        return a.getBirthday().compareTo(b.getBirthday());
    }
}
ComparisonProvider myComparisonProvider = new ComparisonProvider();
Arrays.sort(rosterAsArray, myComparisonProvider::compareByName);
//------------------------
@Test
public void test2() {
    Person person = new Person("Tom", IsoChronology.INSTANCE.date(1995, 6, 20), Person.Sex.MALE, "tom@qq.com");

    Supplier<String> sup = () -> person.getName();
    System.out.println(sup.get());

    System.out.println("===等价于===");

    Supplier<String> sup1 = person::getName;
    System.out.println(sup1.get());
}

String[] stringArray = { "Barbara", "James", "Mary", "John",
    "Patricia", "Robert", "Michael", "Linda" };
Arrays.sort(stringArray, String::compareToIgnoreCase);
//-------------------
@Test
public void test5(){
    BiPredicate<String,String> bp = (x,y)->x.equals(y);
    System.out.println(bp.test("Java情报局","Java情报局1"));
    System.out.println("===等价于===");

    BiPredicate<String,String> bp1 = String::equals;
    System.out.println(bp.test("Java情报局","Java情报局"));
}

public static <T, SOURCE extends Collection<T>, DEST extends Collection<T>>
    DEST transferElements(
        SOURCE sourceCollection,
        Supplier<DEST> collectionFactory) {
        
        DEST result = collectionFactory.get();
        for (T t : sourceCollection) {
            result.add(t);
        }
        return result;
}

Set<Person> rosterSetLambda =
    transferElements(roster, () -> { return new HashSet<>(); });

Set<Person> rosterSet = transferElements(roster, HashSet<Person>::new);
//Java编译器可以推断出要创建包含Person类型元素的HashSet集合，可简写
Set<Person> rosterSet = transferElements(roster, HashSet::new);

Function<Integer,MyClass> fun = (n) -> new MyClass(n);
//等价于
Function<Integer,Person> fun = MyClass::new;
// 带两个参数的构造器引用就要用BiFunction，多个参数的话，还可以自定义一个这样的函数式接口

@Test
public void test6(){
    Supplier<Person> sup = ()->new Person("Tom", IsoChronology.INSTANCE.date(1995, 6, 20), Person.Sex.MALE, "tom@qq.com");
    System.out.println(sup.get());

@Test
public void test7(){
    Function<Integer,String[]> fun = args -> new String[args];
    String[] strs = fun.apply(6);
    System.out.println(strs.length);
    
    System.out.println("===等价于===");
    
    Function<Integer,String[]> fun1 = String[]::new;
    String[] strs1 = fun1.apply(6);
    System.out.println(strs1.length);
}

Person[] rosterAsArray =
    roster.toArray(new Person[roster.size()]);

//Comparator 是一个函数式接口？？
class PersonAgeComparator
    implements Comparator<Person> {
    public int compare(Person a, Person b) {
        return a.getBirthday().compareTo(b.getBirthday());
    }
}

// 实现比较器方法
Arrays.sort(rosterAsArray, new PersonAgeComparator());

// 使用Lambda表达式代替创建实现Comparator的实例类
Arrays.sort(rosterAsArray,
            (Person a, Person b) -> {
                return a.getBirthday().compareTo(b.getBirthday());
            }
           );

// 比较年龄的方法在Person.compareByAge的已经存在，所以可以使用方法引用
Arrays.sort(rosterAsArray, Person::compareByAge);

// 使用方法引用 == 下边简化后的 Lambda 表达式
Arrays.sort(rosterAsArray, (a, b) -> Person.compareByAge(a, b));

// 还可以直接使用Comparator比较器的方法
Arrays.sort(rosterAsArray,Comparator.comparing(Person::getBirthday));

public static long parallelSum(long n) {
    return Stream.iterate(1L, i -> i + 1)
        .limit(n)
        .parallel()    //将流转化为并行流
        .reduce(0L, Long::sum);
}

interface MyFunc<T>{
    T func(int a);

    default String getName(){
        return "hello java8";
    }
}

@Test
public void test1(){
    List<Integer> list = Arrays.asList(22,11,33,55,4);
    //sort是List接口中的默认方法,naturalOrder是Comparator的静态方法
    list.sort(Comparator.naturalOrder());
    for (Integer integer : list) {
        System.out.println(integer);
    }
}

interface MyFunc<T> {
    default String getName() {
        return "hello java8";
    }
}

interface MyFunc1 {
    default String getName() {
        return "hello Java情报局";
    }
}

class MyClass implements MyFunc, MyFunc1 {

    @Override
    public String getName() {
        return MyFunc1.super.getName();
    }
}

@Test
public void test(){

    Optional<Person> optional = Optional.empty();  //创建一个空Optional

    Optional<Person> op = Optional.of(new Person());
    Person p = op.get();
    System.out.println(p);   //Person{name='null', birthday=null, gender=null, emailAddress='null'}

    Person person = null;
    Optional<Person> op1 = Optional.of(person); //person为null，抛出NullPointerException

    Optional<Person> op2 = Optional.ofNullable(person);   //创建允许null值得Optional对象

}

@Test
public void test4(){
    Person person = new Person("Tom",IsoChronology.INSTANCE.date(1999, 7, 15),Person.Sex.FEMALE, "Tom@360.com")
    Optional<Person> op = Optional.ofNullable(person);

    Optional<String> op1 = op.map(Person::getName);
    System.out.println(op1.get());
    
    /**
    * 使用 map 从 optional 对象中提取和转换值
    * 如果想提取人员姓名，之前需要判断persion !=null,Optional提供了一个map方法，对其处理
    **/
    Optional<String> op2 = op.map(Person::getName);
    System.out.println(op2.get());

    //使用 flatMap 链接 optional 对象
    Optional<String> op3 = op.flatMap((e) -> Optional.of(e.getName()));
    System.out.println(op3.get());
    
    //TODO
}

ExecutorService executor = Executors.newCachedThreadPool();
Future<Double> future = executor.submit(new Callable<Double>() {
    public Double call() {
        return doSomeThings();    //异步方式在新的线程中执行操作
    }
});
//doSomethingElse();    //异步操作进行的同时，可以做其他事情
try {
    //获取异步操作的结果，如果阻塞，等1秒后退出
    Double result = future.get(1, TimeUnit.SECONDS);   
} catch (ExecutionException | InterruptedException | TimeoutException e) {
}

import java.lang.annotation.Repeatable;
@Repeatable(Authors.class)
public @interface Author {
    String name();
}

public @interface Authors {
    Author[] value();
}

@Author(name = "Tom")
@Author(name = "Jack")
public class Book {
    public static void main(String[] args) {
        Author[] authors = Book.class.getAnnotationsByType(Author.class);
        Arrays.asList(authors).forEach(s->{
            System.out.println(s.name());
        });
    }
}

@NotNull String name = person.getName();    //getName不返回空

List<@NotNull Person> persons = new ArrayList<>();  //persons总是非空

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>(); 
Optional<Integer> maxValue = Optional.of(map.reduceValues(1, Integer::max));