ENHANCING STRING PERFORMANCE
One of the simplest Java tips is concerning String performance. Most 
Java developers use it.

"Do not use += with Strings 
   instead, use a StringBuffer and its append method."

However, a very important extension can be added to this. It's for 
initializing the StringBuffer to a good initial capacity.

A simple example is a repeat method. This method takes a String 'str' 
and an int 'n', and returns a String in which str has been repeated n 
times.

Here's the sample code:

    public String repeat(String str, int n) { 
        StringBuffer buffer = new StringBuffer(); 
        for(int i=0; i<n; i++) { 
            buffer.append(str); 
        } 
        return buffer.toString(); 
    }

In this scenario, the StringBuffer object will resize its internal 
array many times as the code adds more and more strings. Instead, the 
code should try to help the StringBuffer and tell it how large a String 
it expects. Do this by changing

        StringBuffer buffer = new StringBuffer();

to

        StringBuffer buffer = new StringBuffer(n*str.length());

The performance of routines will increase dramatically by setting a 
realistic initial capacity, which makes extensive use of 
StringBuffer.append.

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