Performance ISSUE of JAVA Code

Question

Hello,
We are having Delphi application. But as per our requirements we have to migrated the Delphi code to java. We have done this but it is consuming the 3 times more time as compare to Delphi Application.
We have used simple primitive types and arrays. But there are some loops which runs 4-8lac (800000) times.
Colud you please suggest me some ways to improve the performance, as it is very critical for me ?
Thanks,
Satbir

Answer 1

We have done this but it is consuming the 3
times more time as compare to Delphi Application.
We have used simple primitive types and arrays. But
there are some loops which runs 4-8lac (800000)
times.Sometimes trying too hard will make things slower.
I have some suggestions:
1) Do not inline functions yourself. This will in the best case have no effect and in the worst case make your code buggy. If your code is written according to good object-oriented methods it is probably not even possible.
2) Don't flog the garbage collector. If your inner loop creates new objects, don't release them for the collector to clean up. Instead put them in a free list and reuse them. For general coding this isn't such a great idea, because the collector can reclaim objects about as efficiently as you can recycle them yourself. But inside a tight loop it can help a lot.
2.1) Objects with finalizers are slow to garbage collect. Avoid finalizers in performance-critical code. (You can use classes that have finalizers, you just don't want them to be garbage collected while in tight code). Some of the classes provided by the Java API have finalizers also.
3) Try using the server VM.
4) Try different versions of the JDK. Some people have found that 1.4 is slower than 1.3, others find it is faster. Both are much faster than 1.2.
5) String operations in Java are very slow. Much slower even than they usually are. StringBuffers can be 4-5 times faster than Strings, but even then string handling is just not fast. See if you can minimize the amount of string handling in your tight loops.
6) Synchronization is quite slow also. It is faster in 1.4, but it is still slow. Don't synchronize unless absolutely necessary. Some synchronized operations can be done instead with volatile variables, unfortunately many things cannot.
7) Make sure you have enough heap space for everything to fit comfortably. If the garbage collector is running during a tight loop, this will kill your performance.
8) Some of the calls to the Java API are very slow. Some standard API classes, such as Hashtable, have synchronized methods, which can cause hidden slowing. Other functions are just plain slow in general.
9) Try using the -Xrunhprof option to profile your code. While it will run much more slowly with the profiler enabled, it will at least indicate where the slowness is. It might not be what you expect.