Java: toString vs. string concatentation?

Question

Is there a reason to prefer either string concatenation or invoking toString when converting objects to string representations?

Does string concatenation cause the object's toString method to be invoked?

String s;
Properties p = System.getProperties();
s = p.toString();
s = "" + p;

Slightly related: http://stackoverflow.com/questions/47605/string-concatenation-concat-vs-operator — Sotirios Delimanolis, Oct 29 '15 at 02:54
@SotiriosDelimanolis, is that a reason to prefer one over the other? It's not a duplicate question. — Mark Harrison, Oct 29 '15 at 02:55
`p.toString()` doesn't involve a new object. `"" + p` involves a new object. (Though I would imagine the `""` could be removed by a smart compiler.) After that, it's all opinion, what looks better. — Sotirios Delimanolis, Oct 29 '15 at 02:56
so your answer is "there's no reason to prefer one over the other"? — Mark Harrison, Oct 29 '15 at 02:57
great. put that in an answer and unmark this as a duplicate! — Mark Harrison, Oct 29 '15 at 02:58
Anything we put in an answer here will repeat what is already stated in the duplicate: _So...very similar things happens in both cases. One just does a little more work._ — Sotirios Delimanolis, Oct 29 '15 at 02:59
lol, everything except the answer to the original question, which was "is one preferrable to the other". — Mark Harrison, Oct 29 '15 at 03:00
I hope you can infer that for yourself given all the details :) — Sotirios Delimanolis, Oct 29 '15 at 03:01
[This is more appropriate.](http://stackoverflow.com/questions/7752347/string-valueof-vs-concatenation-with-empty-string) — Sotirios Delimanolis, Oct 29 '15 at 03:04

score 2 · Accepted Answer · answered Oct 29 '15 at 03:14

2

p.toString() is better.

When you say s=""+p, the compiler makes something like this:

{
    StringBuilder sb = new StringBuilder();
    sb.append("").append(p.toString());
    s=sb.toString();
}

So, yes, ""+p does mean that p.toString() gets called, but it also adds a lot of extra work.

The best thing that can happen is that the compiler recognizes that it's the same as p.toString() and just calls that instead, but you shouldn't count on that.

answered Oct 29 '15 at 03:14

Matt Timmermans

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I think it does `String.valueOf(p)`, not `p.toString()` though the former calls the latter when `p != null`. – Mike Samuel Oct 29 '15 at 03:53

Java: toString vs. string concatentation?

1 Answers1