In Java, how to append a string more efficiently?

Question

I wrote a Java program, in which, I need to append a string

" u13a2" to an existing one "u1234 u12de u1386 ... u15a3".

So gradually the string becomes longer and longer. I found the time spent on each appending also becomes longer and longer. Is there any way that we can improve this to some extend ?

The implementation came to my mind includes:

unicodeArray += " "+unicode;

or

unicodeArray = unicodeArray.concat(" "+unicode);

They gave similar performance. I think the main reason that causes these bad performance is the special type String. It creates a new object for every assignment. If you also think so, does this mean I'd better use another type, like byte array?

Related: http://en.wikipedia.org/wiki/Schlemiel_the_Painter%27s_algorithm — OrangeDog, Oct 15 '12 at 16:34
@SteveKuo Voting to close this redundant question is quicker than posting a complaint. — Basil Bourque, Aug 29 '14 at 03:36

score 109 · Answer 1 · edited May 23 '17 at 12:10

109

You should use the StringBuilder class.

StringBuilder stringBuilder = new StringBuilder();

stringBuilder.append("Some text");
stringBuilder.append("Some text");
stringBuilder.append("Some text");

String finalString = stringBuilder.toString();

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edited May 23 '17 at 12:10

Community

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answered Oct 15 '12 at 16:33

Damian Leszczyński - Vash

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Pradeep Pati · Accepted Answer · 2013-04-20T04:32:31.370

35

Use StringBuilder class. It is more efficient at what you are trying to do.

edited Apr 20 '13 at 04:32

answered Oct 15 '12 at 16:31

Pradeep Pati

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score 8 · Answer 3 · edited Oct 15 '12 at 17:01

8

You can use StringBuffer or StringBuilder for this. Both are for dynamic string manipulation. StringBuffer is thread-safe where as StringBuilder is not.

Use StringBuffer in a multi-thread environment. But if it is single threaded StringBuilder is recommended and it is much faster than StringBuffer.

edited Oct 15 '12 at 17:01

assylias

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answered Oct 15 '12 at 16:32

Subhrajyoti Majumder

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StringBuffer is thread-safe as well. see http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/StringBuffer.html – Pradeep Pati Oct 15 '12 at 16:34
It is the way round: StringBuilder is NOT thread safe whereas StringBuffer is. – assylias Oct 15 '12 at 16:35
But who manipulates a single CharSequence in a concurrent threads? I believe StringBuffer's thread-safety has no usage. – Amir Pashazadeh Apr 20 '13 at 04:49
Its all depend upon requirement. – Subhrajyoti Majumder Apr 21 '13 at 16:19

score 2 · Answer 4 · answered Oct 15 '12 at 16:34

2

- Each time you append or do any modification with it, it creates a new String object.

- So use append() method of StringBuilder(If thread safety is not important), else use StringBuffer(If thread safety is important.), that will be efficient way to do it.

answered Oct 15 '12 at 16:34

Kumar Vivek Mitra

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score 0 · Answer 5 · answered Oct 15 '12 at 16:32

0

java.lang.StringBuilder. Use int constructor to create an initial size.

answered Oct 15 '12 at 16:32

Jeff Miller

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In Java, how to append a string more efficiently?

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