Java map和flatmap

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

public class _1 {
    public static void main(String[] args) {
//        List<String> funs = new ArrayList<String>();
//        funs.add("F");
//        funs.add("U");
//        funs.add("N");
       // funs.stream().forEach(x->System.out.println(x));
//        funs.stream().map(x->x+"001").forEach(x->System.out.println(x));
        //第一个结果是FUN 第二个结果是F001 U001 N001;
        List<String> fun1=new ArrayList<>();
        fun1.add("one");
        fun1.add("two");
        fun1.add("three");
        List<String> fun2=new ArrayList<>();
        fun2.add("four");
        fun2.add("five");
        fun2.add("six");
        List<List<String>> nestedList = new ArrayList<>();
        nestedList.add(fun1);
        nestedList.add(fun2);
       // nestedList.stream().map(x->{return x.stream().map(a->a.toUpperCase());}).forEach(x->x.forEach(a->System.out.println(a)));
        //结果是 ONE TWO THREE FOUR FIVE SIX 太麻烦了！
        //简化结果//nestedList.stream().flatMap(x->x.stream()).map(x->x.toUpperCase()).forEach(s->System.out.print(s));


    }
}