[JAVA] Stream 사용하기(스트림)- 2.가공하기

JAVA - Stream 사용하기 - 가공

https://mangkyu.tistory.com/114

Collection의 Stream 생성

=================================================================================================================  
List<String> list = Arrays.asList("A","B","C","D","E");  
Stream<String> stream0 = list.stream();  
=================================================================================================================  

배열의 Stream 생성

stream4 의경우에는 배열의 0번째부터 4번쨰까지만을 포함하여 생성하므로 A,B,C,D 만 들어가있음  
=================================================================================================================  
Stream<String> stream1 = Stream.of("A","B","C","D","E");  
Stream<String> stream2 = Stream.of(new String []{"A","B","C","D","E"});  
Stream<String> stream3 = Arrays.stream(new String[]{"A","B","C","D","E"});  
Stream<String> stream4 = Arrays.stream(new String[]{"A","B","C","D","E"},0,4);  
=================================================================================================================  

원시 Stream 생성

//원시 스트림 생성 ,int,long,double 가능  
=================================================================================================================  
IntStream intStream = IntStream.range(10,100);  
LongStream longStream = LongStream.range(10,100);  
=================================================================================================================  

가공 - Filter(필터링)

=================================================================================================================  
//stream 가공, Filter 필터링  
Stream<String> filterStream =  
		list.stream()  
		.filter(name ->name.contains("A"));  
filterStream.forEach(System.out::println);  
=================================================================================================================  

가공 - Map (데이터 변환)

=================================================================================================================  
//stream 가공, Map 데이터변환  
Stream<String> mapStream =  
		list.stream()  
		.map(s ->s.toLowerCase());  
mapStream.forEach(System.out::println);  
=================================================================================================================  

가공 - Sorted (데이터 정렬)

sortStream1 - 오름차순  
sortStream2 - 내림차순  
=================================================================================================================  
//stream 가공 , Sorted 정렬  
List<String> sortList = Arrays.asList("AAAAA" , "ZZZZZ" , "EEEEE" , "QQQQQ" , "CCCCC");  
Stream<String> sortStream1= sortList.stream()  
		.sorted();  
sortStream1.forEach(System.out::println);  
  
Stream<String> sortStream2= sortList.stream()  
		.sorted(Comparator.reverseOrder());  
sortStream2.forEach(System.out::println);  
  
=================================================================================================================  

가공 - Distinct (중복제거)

=================================================================================================================  
//stream 가공 , Distinct 중복제거  
List<String> distinctList = Arrays.asList("AA","BB","CC","AA","CC","DD");  
Stream<String> distinctStream = distinctList.stream()  
		.distinct();  
distinctStream.forEach(System.out::println);  
=================================================================================================================  

가공 - Peek (특정 연산 수행)

=================================================================================================================  
int sum = IntStream.of(1,2,3,4,5,6,7,8,9,10)  
		.peek(System.out::println)  
		.sum();  
System.out.println(sum);  
=================================================================================================================  

가공 - Stream 변환

원시Stream < - > Stream 변환  
=================================================================================================================  
//stream 가공 , Stream < - > 원시 Stream 변환  
Stream<String> changeStream1 = IntStream.range(1,10)  
		.mapToObj(i->"NUMBER : "+i);  
changeStream1.forEach(System.out::println);  
  
Stream<String> changeStream2 = Stream.of(1.0,2.0,3.0)  
		.mapToInt(Double::intValue)  
		.mapToObj(i->"NUMBER : " + i);  
changeStream2.forEach(System.out::println);  
=================================================================================================================  

소스코드

=================================================================================================================  
package com.sungchul;  
  
import java.util.Arrays;  
import java.util.Comparator;  
import java.util.List;  
import java.util.stream.DoubleStream;  
import java.util.stream.IntStream;  
import java.util.stream.LongStream;  
import java.util.stream.Stream;  
  
public class StreamApiTestClass {  
	public static void main(String []args){  
		//스트림 생성  
		List<String> list = Arrays.asList("A","B","C","D","E");  
		Stream<String> stream0 = list.stream();  
		Stream<String> stream1 = Stream.of("A","B","C","D","E");  
		Stream<String> stream2 = Stream.of(new String []{"A","B","C","D","E"});  
		Stream<String> stream3 = Arrays.stream(new String[]{"A","B","C","D","E"});  
		Stream<String> stream4 = Arrays.stream(new String[]{"A","B","C","D","E"},0,4);  
  
		//원시 스트림 생성 ,int,long,double 가능  
		IntStream intStream = IntStream.range(10,100);  
		LongStream longStream = LongStream.range(10,100);  
  
		//stream 가공, Filter 필터링  
		Stream<String> filterStream = list.stream()  
				.filter(name ->name.contains("A"));  
		filterStream.forEach(System.out::println);  
  
		//stream 가공, Map 데이터변환  
		Stream<String> mapStream = list.stream()  
				.map(s ->s.toLowerCase());  
		mapStream.forEach(System.out::println);  
  
		//stream 가공 , Sorted 정렬  
		List<String> sortList = Arrays.asList("AAAAA" , "ZZZZZ" , "EEEEE" , "QQQQQ" , "CCCCC");  
		Stream<String> sortStream1= sortList.stream()  
				.sorted();  
		sortStream1.forEach(System.out::println);  
  
		Stream<String> sortStream2= sortList.stream()  
				.sorted(Comparator.reverseOrder());  
		sortStream2.forEach(System.out::println);  
  
		//stream 가공 , Distinct 중복제거  
		List<String> distinctList = Arrays.asList("AA","BB","CC","AA","CC","DD");  
		Stream<String> distinctStream = distinctList.stream()  
				.distinct();  
		distinctStream.forEach(System.out::println);  
  
		//stream 가공 , Peek 특정 연산하기  
		int sum = IntStream.of(1,2,3,4,5,6,7,8,9,10)  
				.peek(System.out::println)  
				.sum();  
		System.out.println(sum);  
  
		//stream 가공 , Stream < - > 원시 Stream 변환  
		Stream<String> changeStream1 = IntStream.range(1,10)  
				.mapToObj(i->"NUMBER : "+i);  
		changeStream1.forEach(System.out::println);  
  
		Stream<String> changeStream2 = Stream.of(1.0,2.0,3.0)  
				.mapToInt(Double::intValue)  
				.mapToObj(i->"NUMBER : " + i);  
		changeStream2.forEach(System.out::println);  
  
		//stream0.forEach(System.out::println);  
		//stream4.forEach(System.out::println);  
  
	}  
  
}  
=================================================================================================================  

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JAVA - Stream 사용하기 - 가공

Collection의 Stream 생성

배열의 Stream 생성

원시 Stream 생성

가공 - Filter(필터링)

가공 - Map (데이터 변환)

가공 - Sorted (데이터 정렬)

가공 - Distinct (중복제거)

가공 - Peek (특정 연산 수행)

가공 - Stream 변환

소스코드