Is String Concatenation memory efficient?

Question

Which is more memory efficient:
Concatenating two Strings, or just having one String with both values in it?
My code below gives an example of both cases.
Thank you in advance.
https://code.sololearn.com/cdqv4F5k2GWF/?ref=app

Answer 1

Of course creating less variables is more memory efficient so if you can have one string don't create two of them.

Answer 2

Ok, then what about
String x = “HelloWorld”;
String y = “Hello” + “World”;
Which is more efficient. x or y?

Answer 3

this is the same