static int outerStaticNum;

int outerNum;

public static void main(String[] args) {

//1. Default Method for interface

Formula formula = new Formula() {

@Override

public double calculate(int a) {

return sqrt(a * 100);

}

};

formula.calculate(100); // 100.0

formula.sqrt(16); // 4.0

//2. Lambda before

List<String> names = Arrays.asList("peter", "anna", "mike", "xenia");

Collections.sort(names, new Comparator<String>() {

@Override

public int compare(String a, String b) {

return b.compareTo(a);

}

});

names.forEach(System.out::println);

//2-3. Lambda expression3

Collections.sort(names, (a, b) -> b.compareTo(a));

names.forEach(System.out::println);

//3. functional interfaces

Converter<String, Integer> converter1 = (from) -> Integer.valueOf(from);

Integer converted1 = converter1.convert("123");

System.out.println(converted1); // 123

//4-1. method reference

Something something = new Something();

Converter<String, String> converter2 = something::startsWith;

String converted2 = converter2.convert("Java");

System.out.println(converted2); // "J"

//4-2. constructor reference

PersonFactory<Person> personFactory = Person::new;

Person person = personFactory.create("Peter", "Parker");

System.out.println(person.firstName + " " + person.lastName);

//5. lambda scopes

//5-1. local variables

int num = 1;

Converter<Integer, String> stringConverter1 =

(from) -> String.valueOf(from + num);

stringConverter1.convert(2); // 3

//5-2. fields and static variables Test

Lambda4 lambda4 = new Lambda4();

lambda4.testScopes();

//lambda scopes

//5-3. default methods

//Formula formula2 = (a) -> sqrt(a * 100); //COMPILE ERROR!!

//6. built-in functional interfaces

//6-1. Predicates

Predicate<String> predicate = (s) -> s.length() > 0;

predicate.test("foo"); // true

predicate.negate().test("foo"); // false

Predicate<Boolean> nonNull = Objects::nonNull;

Predicate<Boolean> isNull = Objects::isNull;

Predicate<String> isEmpty = String::isEmpty;

Predicate<String> isNotEmpty = isEmpty.negate();

nonNull.test(null); //false

//6-2. Functions

Function<String, Integer> toInteger = Integer::valueOf;

Function<String, String> backToString = toInteger.andThen(String::valueOf);

backToString.apply("123"); // "123"

//6-3. Suppliers

Supplier<Person> personSupplier = Person::new;

personSupplier.get(); // new Person

//6-4. Consumers

Consumer<Person> greeter = (p) -> System.out.println("Hello, " + p.firstName);

greeter.accept(new Person("Luke", "Skywalker"));

//6-5. Comparator

Comparator<Person> comparator = (p1, p2) -> p1.firstName.compareTo(p2.firstName);

Person p1 = new Person("John", "Doe");

Person p2 = new Person("Alice", "Wonderland");

comparator.compare(p1, p2); // > 0

comparator.reversed().compare(p1, p2); // < 0

//6-6. Optional

Optional<String> optional = Optional.of("bam"); //of():null이 아닌 명시된 값을 가지는 Optional 객체 반환

optional.isPresent(); // true //Optional 객체에 저장된 값이 null인지 확인

optional.get(); // "bam" //Optional 객체에 저장된 값 접근

optional.orElse("fallback"); // "bam" //저장된 값이 존재-> 값반환, 없으면-> 인수 값 반환

optional.ifPresent((s) -> System.out.println(s.charAt(0))); // "b"

//7. Stream

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

stringCollection.add("ddd2");

stringCollection.add("aaa2");

stringCollection.add("bbb1");

stringCollection.add("aaa1");

stringCollection.add("bbb3");

stringCollection.add("ccc");

stringCollection.add("bbb2");

stringCollection.add("ddd1");

//7-1.Filter

stringCollection

.stream()

.filter((s) -> s.startsWith("a"))

.forEach(System.out::println); // "aaa2", "aaa1"

//7-2. Sorted

stringCollection

.stream()

.sorted()

.filter((s) -> s.startsWith("a"))

.forEach(System.out::println); // "aaa1", "aaa2"

System.out.println(stringCollection); // ddd2, aaa2, bbb1, aaa1, bbb3, ccc, bbb2, ddd1

//7-3. Map

stringCollection

.stream()

.map(String::toUpperCase)

.sorted((a, b) -> b.compareTo(a))

.forEach(System.out::println); // "DDD2", "DDD1", "CCC", "BBB3", "BBB2", "AAA2", "AAA1"

//7-4. Match

boolean anyStartsWithA =

stringCollection

.stream()

.anyMatch((s) -> s.startsWith("a"));

System.out.println(anyStartsWithA); // true

boolean allStartsWithA =

stringCollection

.stream()

.allMatch((s) -> s.startsWith("a"));

System.out.println(allStartsWithA); // false

boolean noneStartsWithZ =

stringCollection

.stream()

.noneMatch((s) -> s.startsWith("z"));

System.out.println(noneStartsWithZ); // true

//7-5. Count

long startsWithB =

stringCollection

.stream()

.filter((s) -> s.startsWith("b"))

.count();

System.out.println(startsWithB); // 3

//7-6. Reduce

Optional<String> reduced =

stringCollection

.stream()

.sorted()

.reduce((s1, s2) -> s1 + "#" + s2);

reduced.ifPresent(System.out::println); // "aaa1#aaa2#bbb1#bbb2#bbb3#ccc#ddd1#ddd2"

//Map

Map<Integer, String> map = new HashMap<>();

for (int i = 0; i < 10; i++) {

map.putIfAbsent(i, "val" + i);

}

map.forEach((id, val) -> System.out.println(val));

}