Each time an object is operated in Java, it goes into the area of memory named as heap. The Java heap is named the garbage collectable heap. The garbage collection may not be forced. The garbage collector applies in low memory situations. When it runs, it removes the memory allocated by an unreachable object. The garbage collector gives on a low priority daemon thread. You may simply ask the garbage collector to collect garbage by calling System.gc() but you can't handle it.
An object's life has no meaning unless something has papered to it. If you can't handle it then you can't ask it to do anything. Then the object becomes unreachable and the garbage collector will noted it out. Java automatically reads all the unreachable objects periodically and removes the memory consumed by those unreachable objects to be needed by the future reachable objects.