Optimize String += or Concat?

Question

I am writing a file with possibly 1000 data points. I have classes for all of these and am currently writing all of the data at the end (the datapoints are taken at 1s intervals). What I am currently doing is written below, and it's very slow. Would I be better off changing how I am writing the string/bytes to the file? Or would I be better off writing this information to some file pointer as the application is running?

Btw, all of the things such as getAccuracy() and such are floats/ints (so it has to convert those also).

fileStr = "";
        fileStr += "timestamp,Accuracy,Altitude,Latitude,Longitude,GPSSatelliteEntries\r\n";
        for (Iterator<Entry> i = entries.iterator(); i.hasNext(); ) {
            Entry item = i.next();
            long ts = item.getTs();
            DataEntry d = item.getD();
            List<GPSSatelliteEntry> satellites = item.getG();

            // write stuff
            fileStr += ts + ",";
            fileStr += d.getAccuracy() + "," + d.getAltitude() + "," + d.getLatittude() + "," + d.getLongitude() + ",";
            fileStr += "[";
            boolean entered = false;
            for (Iterator<GPSSatelliteEntry> j = satellites.iterator(); j.hasNext(); ) {
                GPSSatelliteEntry item2 = j.next();
                entered = true;
                fileStr += "(" + item2.getAzimuth() + "," + item2.getElevation() + "," + item2.getPrn() + "," + item2.getSnr() + "),";
            }
            // chop off extra ,
            if (entered)
                fileStr = fileStr.substring(0, fileStr.length() - 1);
            fileStr += "]";
            fileStr += "\r\n";
        }

For ints and floats (or Integer and Float) I would recommend using String.valueOf() — Menno, Apr 12 '13 at 20:21
See http://stackoverflow.com/questions/47605/java-string-concatenation-concat-vs-operator?rq=1 — ddmps, Apr 12 '13 at 20:24
@Aquillo So you wouldn't recommend using `Float.toString()` and `Integer.toString()`? — MasterGberry, Apr 12 '13 at 20:25
@MasterGberry If they are primitives, use `toString()`, otherwise use `String.valueOf()` — Sotirios Delimanolis, Apr 12 '13 at 20:30
@MasterGberry, In fact it doesn't matter, the toString() function is the same as the String.valueOf() function. The advantage of `String.valueOf()` is that it doesn't matter if it's an int or a float (more or less readability). — Menno, Apr 12 '13 at 20:42

Simon Dorociak · Accepted Answer · 2013-04-12T20:47:57.193

4

Everytime you have hard work with Strings, use StringBuilder or StringBuffer to achieve better performance .

Don't forget that String is immutable, and each time you modify String new instance will be created and it costs performance.

edited Apr 12 '13 at 20:47

answered Apr 12 '13 at 20:20

Simon Dorociak

33,374
10
68
106

What exactly is "hard work"? If String is immutable, then how can it be modified? And how does creating a new `String" "costs performance"? – Steve Kuo Apr 16 '13 at 17:06
Any work is hard, I suggest doing as little of it as possible. Creating a new string "costs performance" because there are operations related to memory allocation, pointers, and other things that happen when you create one. Using something like a StringBuilder will allow you to save this overhead because you are using a single object. When applied over a large data set you can see significant differences in performance. – RacerNerd Apr 19 '13 at 21:39

score 0 · Answer 2 · answered Apr 12 '13 at 20:19

0

Most probably string buffer

A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified.

or go for string builder

answered Apr 12 '13 at 20:19

Suresh Atta

120,458
37
198
307

score 0 · Answer 3 · answered Apr 12 '13 at 20:22

0

StringBuilder stuff = new StringBuilder();
stuff.append("PUT YOUR STRINGS HERE");
stuff.append("PUT YOUR STRINGS HERE");

Then you can use 'stuff' to print the strings. Put it in a loop and iterate over a large number with a timer to see the advantages, it's pretty interesting.

answered Apr 12 '13 at 20:22

RacerNerd

1,579
1
13
31

1

Or chaining ofcourse, which in this case might just be useful. – Menno Apr 12 '13 at 20:23
Chaining is an excellent suggestion here. Chaining rather than using string concatenation within each call to append will save cycles. – RacerNerd Apr 19 '13 at 21:33

Optimize String += or Concat?

3 Answers3