One of the challenges in adopting SWT is that native resources must be freed when they are no longer needed. Unlike AWT or Swing, which perform these operations automatically when an object is garbage collected, SWT needs manual resource management.
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Why does SWT need manual resource management?
A common question asked is why SWT has this rule, when Java has had perfectly acceptable garbage collection for many years. In part, it's because SWT predated acceptable garbage collection, but it's also to try and return native resources as soon as they are no longer needed.
From a performance perspective, adding a finalize() method to an object also causes the garbage collector to work harder; much of the speed in today's garbage collectors are because they don't need to call methods, as they are invariably missing. It also hurts in SWT's case because the object must post its dispose request onto the UI thread, which delays its garbage collection as the object becomes reachable...