54

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?

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  • 3
    Related: en.wikipedia.org/wiki/Schlemiel_the_Painter%27s_algorithm Commented Oct 15, 2012 at 16:34
  • 9
    How many duplicate StringBuilder answers do we need? Commented Oct 15, 2012 at 16:51
  • 2
    @SteveKuo Voting to close this redundant question is quicker than posting a complaint. Commented Aug 29, 2014 at 3:36
  • Awesome link, @OrangeDog Commented Aug 29, 2014 at 5:50

5 Answers 5

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115

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();

In addition, please visit:

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36

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

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9

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.

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4 Comments

StringBuffer is thread-safe as well. see docs.oracle.com/javase/1.5.0/docs/api/java/lang/…
It is the way round: StringBuilder is NOT thread safe whereas StringBuffer is.
But who manipulates a single CharSequence in a concurrent threads? I believe StringBuffer's thread-safety has no usage.
Its all depend upon requirement.
3

- 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.

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0

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

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