Study Java

1. 성별을 키값으로 리스트 그룹핑 하기 public class Person { enum Gender{ MALE, FEMALE } enum City{ Seoul, Pusan } private String name; private Gender gender; private int score; private City city; public Person(String name, int score, Gender gender) { this.name = name; this.score = score; this.gender = gender; } public Person(String name, int score, Gender gender, City city) { this.name = name; this.gender = ge..

Java 2020. 6. 18. 16:26

1. toList() import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class ToListExam { public static void main(String[] args) { List personList = Arrays.asList( new Person("lee",9, Person.Gender.MALE), new Person("kim",5, Person.Gender.FEMALE), new Person("park",6, Person.Gender.FEMALE), new Person("sin",3, Person.Gender.FEMALE), new Person("hong",4, Person.Gen..

Java 2020. 6. 18. 13:45

1. public final OptionalInt reduce(IntBinaryOperator op) import java.util.Arrays; import java.util.List; import java.util.function.IntBinaryOperator; public class ReduceExam { public static void main(String[] args) { List list = Arrays.asList( new Person("hong",99), new Person("park",82), new Person("lee",87), new Person("kim",77) ); // XXXBinaryOperator - applyAsXXX int sum = list.stream().mapT..

Java 2020. 6. 18. 12:53

orElse import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class OptionalExam { public static void main(String[] args) { // orElse List list1 = new ArrayList(); double result1 = list1.stream().mapToInt(Integer::intValue).average() .orElse(0); // 값이 있으면 값을 저장하고 없다면 0을 저장 System.out.println("result1 : "+result1); List list2 = Arrays.asList(88,93,77,88); double result..

Java 2020. 6. 18. 12:10

import java.util.Arrays; public class MatchExam { public static void main(String[] args) { int[] arr = {2,4,6,8}; // 스트림을 통과한 객체수 long count = Arrays.stream(arr).count(); System.out.println("스트림을 통과한 객체 수 : "+count); // 모든 객체의 합 long sum = Arrays.stream(arr).sum(); System.out.println("합계 : " + sum); // average()의 리턴값 : OptionalDouble // getAsDouble()은 OptionalDouble타입을 Double타입으로 바꿔준다. double av..

Java 2020. 6. 18. 10:54

1.allMatch package Chap35.Stream.Exam07; import java.util.Arrays; public class MatchExam { public static void main(String[] args) { int[] arr = {2,4,6,8}; // 모두 짝수인가 boolean r = Arrays.stream(arr).allMatch(i->i%2==0); System.out.println(r); } } 파라미터 : IntPredicate boolean r = Arrays.stream(arr).allMatch(new IntPredicate() { @Override public boolean test(int value) { return value%2==0; } }); 2. a..

Java 2020. 6. 18. 10:30

import java.util.Arrays; public class PeekExam { public static void main(String[] args) { int[] arr = {1, 2, 3, 6, 9, 12, 17, 15}; Arrays.stream(arr).peek(System.out::println); // 동작하지 않는다. // peek은 중간처리 메소드이므로 최총처리 메소드를 호출해야 동작한다. int sum = Arrays.stream(arr).peek(s->System.out.println("peek : "+ s)).sum(); System.out.println("합 : " + sum); } }

Java 2020. 6. 18. 09:51

1. 기본타입 import java.util.Arrays; import java.util.List; import java.util.stream.IntStream; public class SortedExample { public static void main(String[] args) { int[] arr = {1,8,4,7,9,6,10}; IntStream intStream = Arrays.stream(arr); intStream.sorted().forEach(System.out::println); } } 2. 참조타입 public class Person implements Comparable{ private String name; private int score; public Person(String ..

Java 2020. 6. 18. 09:42