Question

Is there any possibility that a object which is not referenced anywhere and still existing on heap. I mean is there a possibility that a unused object getting escaped from garbage collector and be there on the heap until the end of the application.

Wanted to know because if it is there, then while coding i can be more cautious.

Answer 1

If an object is no longer referenced, it does still exist on the heap, but it is also free to be garbage-collected (unless we are talking Class objects, which live in PermGen space and never get garbage-collected – but this is generally not something you need to worry about).

There is no guarantee on how soon that will be, but your application will not run out of memory before memory from those objects is reclaimed.

However, garbage collection does involve overhead, so if you are creating more objects than you need to and can easily create less, then by all means do so.

Edit: in response to your comment, if an object is truly not referenced by anything, it will be reclaimed during garbage collection (assuming you are using the latest JVM from Sun; I can’t speak toward other implementations). The reason why is as follows: all objects are allocated contiguously on the heap. When GC is to happen, the JVM follows all references to “mark” objects that it knows are reachable – these objects are then moved into another, clean area. The old area is then considered to be free memory. Anything that cannot be found via a reference cannot be moved. The point is that the GC does not need to “find” the unreferenced objects. If anything, I would be more worried about objects that are still referenced when they are not intended to be, which will cause memory leaks.