Flutter: how to use if else

i want to make a text that change if the _height is 150 , how can i do it? , just have expirence in java , i know my code is whack xD

Container(
child: Column(mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[

if (_height==150.0) {
  Text("hello flutter")
}

else {
  Text("hello world")
 }
],),),