Difference between string.concat and the + operator in string concatenation

Question

(This question may be a duplicate but I really didn't understand the other answers)

You have the following code:

String str ="football";
str.concat(" game");
System.out.println(str); // it prints football

But with this code:

String str ="football";
str = str + " game";
System.out.println(str); // it prints football game

So what's the difference and what's happening exactly?

You didn't assign `str.concat(" game");` to a variable, so `str` still has its original value. — TFrazee, May 31 '18 at 14:44
Strings are imutable, so you have to assing `str.concat(" game");` to a variable — Lino, May 31 '18 at 14:46

score 4 · Accepted Answer · answered May 31 '18 at 14:44

4

str.concat(" game"); has the same meaning as str + " game";. If you don't assign the result back somewhere, it's lost. You need to do:

str = str.concat(" game");

answered May 31 '18 at 14:44

Karol Dowbecki

So what happened exactly is the following? : str.concat(" game") created a new string object "football game" But it didn't change the str reference, and str still refer to "football" – Basel Qarabash May 31 '18 at 14:50
@BaselQarabash yes – Karol Dowbecki May 31 '18 at 14:51

score 2 · Answer 2 · answered May 31 '18 at 14:44

2

The 'concat' function is immutable, so the result of it must be put in a variable. Use:

str = str.concat(" game");

answered May 31 '18 at 14:44

actunderdc

4

Just a small thing: `String`s are imutable, not the `concat` function – Lino May 31 '18 at 14:47

2 Answers2