Premature optimization is an root of all evil

This post is for them who is obsessed with performance of there Java application

most people complaint that Java is slow, but after years of experience in Java i can say that Java itself is not slow, poorly written applications are slow. 

Things you should do when you code any application in Java

Java is mostly used as a Server side technology, but if you are making a Desktop application or providing a client application for you web application then you must consider the following suggestions

1. Always run you Swing GUI on EDT(Event Dispatching Thread) and perform your heavy task such as copying a long file or loading a heavy file in a editor using SwingWorker.

WHY SO ?

If you fully understand the Swing Rendering then you should not ask this question

In case if you don't then 

painting of Swing components must happen on the EDT. By calling synchronous paint methods, your code is implying that it is on the correct thread so that the right things will happen at the right time. If the calling code is not on that correct thread, the results could be undefined.

2. prefer Task & ExecutorService over Threads

ExecutorService manage Threads on your behalf it has capabilities to restrict number of threads to be ever created For e.g: if you have a production Server which is heavily loaded all times then this method will help you much because it will only create Threads you mentions which will provide room for others to run there own task and life will be more easier ....

Explaining every thing about concurrency framework is beyond the scope of this post

3. Prefer for each loop over traditional for loop
Although many compilers perform loop fusion techniques to improve performance of for loop it is also necessary to minimize the scope of variable using this technique

// No longer the preferred idiom to iterate

//over an array!
for (int i = 0; i < a.length; i++) {
doSomething(a[i]);
}

These idioms are better than while loops, but they aren’t perfect. The iterator and the index variables are both just clutter. Furthermore, they represent opportunities for error. The iterator and the index variable occur three times in each loop, which gives you two chances to get them wrong. If you do, there is no guarantee that the compiler will catch the problem. The for-each loop, introduced in release 1.5, gets rid of the clutter and the opportunity for error by hiding the iterator or index variable completely. The resulting idiom applies equally to collections and arrays:

// The preferred idiom for iterating over 
//collections and arrays
for (Element e : elements) {
doSomething(e);
}

When you see the colon (:), read it as “in.” Thus, the loop above reads as “for each element e in elements.” Note that there is no performance penalty for using the for-each loop, even for arrays. In fact, it may offer a slight performance advantage over an ordinary for loop in some circumstances, as it computes the limit of the array index only once.

There are more things but i m running out of time ....!! Ta Ta...