package java8Test;
import java.util.*;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
// https://winterbe.com/posts/2014/03/16/java-8-tutorial/
public class Main {
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 names = Arrays.asList("peter", "anna", "mike", "xenia");
Collections.sort(names, new Comparator() {
@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 converter1 = (from) -> Integer.valueOf(from);
Integer converted1 = converter1.convert("123");
System.out.println(converted1); // 123
//4-1. method reference
Something something = new Something();
Converter converter2 = something::startsWith;
String converted2 = converter2.convert("Java");
System.out.println(converted2); // "J"
//4-2. constructor reference
PersonFactory 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 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 predicate = (s) -> s.length() > 0;
predicate.test("foo"); // true
predicate.negate().test("foo"); // false
Predicate nonNull = Objects::nonNull;
Predicate isNull = Objects::isNull;
Predicate isEmpty = String::isEmpty;
Predicate isNotEmpty = isEmpty.negate();
nonNull.test(null); //false
//6-2. Functions
Function toInteger = Integer::valueOf;
Function backToString = toInteger.andThen(String::valueOf);
backToString.apply("123"); // "123"
//6-3. Suppliers
Supplier personSupplier = Person::new;
personSupplier.get(); // new Person
//6-4. Consumers
Consumer greeter = (p) -> System.out.println("Hello, " + p.firstName);
greeter.accept(new Person("Luke", "Skywalker"));
//6-5. Comparator
Comparator 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 optional = Optional.of("bam"); //of():nullì´ ì•„ë‹Œ ëª…ì‹œëœ ê°’ì„ ê°€ì§€ëŠ” Optional ê°ì²´ 반환
optional.isPresent(); // true //Optional ê°ì²´ì— ì €ìž¥ëœ ê°’ì´ nullì¸ì§€ 확ì¸
optional.get(); // "bam" //Optional ê°ì²´ì— ì €ìž¥ëœ ê°’ ì ‘ê·¼
optional.orElse("fallback"); // "bam" //ì €ìž¥ëœ ê°’ì´ ì¡´ìž¬-> 값반환, 없으면-> ì¸ìˆ˜ ê°’ 반환
optional.ifPresent((s) -> System.out.println(s.charAt(0))); // "b"
//7. Stream
List 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 reduced =
stringCollection
.stream()
.sorted()
.reduce((s1, s2) -> s1 + "#" + s2);
reduced.ifPresent(System.out::println); // "aaa1#aaa2#bbb1#bbb2#bbb3#ccc#ddd1#ddd2"
//Map
Map map = new HashMap<>();
for (int i = 0; i < 10; i++) {
map.putIfAbsent(i, "val" + i);
}
map.forEach((id, val) -> System.out.println(val));
}
}