Re: how can i optimize the given below code

Piotr Kobzda <>
Thu, 20 Mar 2008 22:44:09 +0100
Patricia Shanahan wrote:

Lew wrote:

Joshua Cranmer wrote: wrote:

String value="";
if(value.length() == 0) {
            char data[]=new char[count];
            for(int c=0;c<count;c++){
            value=new String(data);

Why do you want to optimize this code? Have you profiled to make sure
that it is these lines specifically that are the bottleneck?

If speed really is an issue, then the only thing that jumps out at me
for optimizing is getting rid of the for loop:

java.util.Arrays.fill(data, '0');

Is that faster? Enough faster?

It may be faster, depending on the system. The only way to tell if it is
enough faster is for the OP to measure it.

Many systems have a very fast way of pushing a repeated bit pattern to
an area of memory. For example, on Sun SPARC systems, 64 byte chunks of
memory can be written from the floating point registers.

If the OP's system has some such facility, and Arrays.fill is
implemented on that system as a native method using an optimized memory
write method, then it may be significantly faster than than writing one
char at a time.

You right. However, the reference implementation of Arrays.fill() (I
mean the one from the Sun) is implemented as a simple loop filling an
array slot by slot.

A few years ago I wrote an alternative version of the array fill based
on System.arraycopy(), which without an extra optimizations normally
performed by the server JVM is even 5 times faster (sometimes more) than
the original Arrays.fill() implementation. (The server JVM usually
still executes it faster, but it's not as significant as in a case of
the client JVM -- typically not faster than 2 times.)

The original algorithm is there:
The thread includes also a performance test driver, and some test
results. (Sorry, the thread is in Polish. But at least the code should
be clear for everyone, I hope...)


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