[stream] 플랫맵 예시

import java.io.*;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class z31 {

    public static void main(String[] args) {

int[][] arr = {{1,2},{3,4}};
        Arrays.stream(arr).flatMapToInt(a->Arrays.stream(a)).forEach(System.out::println);


    }
}