Is this the most efficient way to append a character array to a string?

Question

I want to read an input stream with a buffer and append each buffer to a string until the stream is empty.

char[] buffer = new char[32];

while ((bytesRead = streamReader.read(buffer, 0, 32)) != -1)
   message += new String(buffer);

I couldn't find a method of String to append a character array directly and opted for this. Is there a way to know if this is wasting cycles copying the character array to a new string, only to immediately discard it?

This may be premature optimization but it glares at me pretty strongly.

I believe this constructor calls Arrays.copyOf().

Use StringBuilder and its append methods instead of `message += new String(buffer);` — Pshemo, Apr 07 '19 at 23:08
Possibly related: [Why StringBuilder when there is String?](https://stackoverflow.com/q/5234147) — Pshemo, Apr 07 '19 at 23:10
The copying to a String does an extra copy, but is nowhere near as expensive as accumulating into a String instead of a StringBuilder. Also, StringBuilder can append a `char[]` directly, so that's two reasons you should be using StringBuilder. — Louis Wasserman, Apr 07 '19 at 23:12
You will find over a large file that this is about the worst way to do it, not the best. — user207421, Apr 07 '19 at 23:17

score 1 · Answer 1 · answered Apr 07 '19 at 23:23

No.

There are more efficient ways. Using a java.util.StringBuilder in your loop is more efficient as it is performing a series of operations. In your loop, += will create another String object each time. For example, if you were to do String d = a + b + c + d... for 1_000_000 Strings, then you'd be making 1_000_000 String objects as waste. Strings are immutable.

Is this the most efficient way to append a character array to a string?

1 Answers1