Doesn't work stdout.write Method but can work stdout.writeln

Question

import 'dart:io'
void main(){
stdout.write("abc");}

that code doesn't worked but

void main(){
stdout.writeln("abc");}

was work!! output is "abc" and

void main(){
stdout.write("abc");
stdout.writeln("def");}

out put is "abcdef" I can't understand this happend...