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From: Jan Burse <janburse@fastmail.fm>
Newsgroups: comp.lang.java.programmer
Subject: Re: StringBuilder
Date: Mon, 05 Sep 2011 05:27:15 +0200
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bob schrieb:
> Is there any way to use StringBuilder but with + signs instead of
> append?

The + in Java does already internally use StringBuilder.

There is only an issue when you want to accumulate a string
value. If you then explicitly use StringBuilder you are
faster, because you save the new StringBuilder() and toString().

So this is faster, since it uses 1 new and 1 toString():

     StringBuilder buf=new StringBuilder();
     for (int i=0; i<100; i++) {
        buf.append(i);
        buf("*");
        buf.append(i);
        buf.append("=");
        buf.append((i*i));
        buf.append("\n");
     }
     System.out.println(buf.toString());

Whereby this code is slower:

     String res="";
     for (int i=0; i<100; i++) {
        res+=i+"*"+i+"="+(i*i)+"\n";
     }
     System.out.println(res);

It is translated to the following code by the compiler, and
thus uses 100 new and 100 toString():

     String res="";
     for (int i=0; i<100; i++) {
         StringBuilder _buf=new StringBuilder(res);
         _buf.append(i);
         _buf("*");
         _buf.append(i);
         _buf.append("=");
         _buf.append((i*i));
         _buf.append("\n");
         res=_buf.toString();
     }
     System.out.println(res);

For more information see for example here:
http://caprazzi.net/posts/java-bytecode-string-concatenation-and-stringbuilder/

Best Regards