File APIs for Java Developers
Manipulate DOC, XLS, PPT, PDF and many others from your application.
The moose likes Beginning Java and the fly likes StringBuffer question Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Java » Beginning Java
Bookmark "StringBuffer question" Watch "StringBuffer question" New topic

StringBuffer question

Jeff Kilbride

Joined: Apr 24, 2001
Posts: 7
I've always had a nagging question about StringBuffers. Is the following initialization an okay thing to do? Or am I creating a bunch of unneccessary string objects -- where a and b are runtime variables, like request parameters?
String a = "the";
String b = "a";
StringBuffer s = new StringBuffer(a + " dog ate " + b + " bone.");
Or would I be better off doing:
StringBuffer s = new StringBuffer(25);
s.append(" dog ate ");
s.append(" bone.");
Or does it matter? I tend to use the first when building StringBuffers from variables, but am afraid I am creating a lot of extra strings...
Bosun Bello
Ranch Hand

Joined: Nov 06, 2000
Posts: 1510
I am not really sure on this one. It may not really matter though, because I know when you concatenate/create strings using the "+" sign, it actually uses a StringBuffer object in the background to get it's job done.

So much trouble in the world -- Bob Marley
Dirk Schreckmann

Joined: Dec 10, 2001
Posts: 7023
By no means do I pretend to be an authority on efficiency. In that light, here are my two cents...
From the API Specification for StringBuffer:

String buffers are used by the compiler to implement the binary string concatenation operator +. For example, the code:
x = "a" + 4 + "c"
is compiled to the equivalent of:
x = new StringBuffer().append("a").append(4).append("c").toString()

Looking further at the documentation, StringBuffer.append(Object - or String) creates a new StringBuffer object.
So, it would seem to me, that looking at the first style:
StringBuffer s = new StringBuffer(a + " dog ate " + b + " bone.");
a + " dog ate " + b + " bone." creates one new String object from this:
new StringBuffer.append(a).append(" dog ate ").append(b).append(" bone.")
while creating 5 new StringBuffer objects (one from the implicit call to new StringBuffer plus one for each call to append) plus one more for your explicit call to new StringBuffer(String) - bringing the total to 6 StringBuffer objects.
Now, your second style:
StringBuffer s = new StringBuffer(25);
s.append(" dog ate ");
s.append(" bone.");
would seem to create first one StringBuffer from new StringBuffer(int) and then one more for each call to append - a total of 5 StringBuffer objects and no "extra" String objects.
Of course, I don't know what I'm talking about.
Good Luck,
-Dirk Schreckmann

[How To Ask Good Questions] [JavaRanch FAQ Wiki] [JavaRanch Radio]
Chris Stewart
Ranch Hand

Joined: Sep 29, 2001
Posts: 124
Your second implementation would be the best route. Later on, when you use strings *cough* JavaMail *cough* you'll be happy you know StringBuffer rather well. From my understanding, it's the most efficent way to create and include multiple strings.
Don't get me started about those stupid light bulbs.
subject: StringBuffer question
It's not a secret anymore!