Question

As a newly created object is allocated to new generation. Is it possible a newly created object is allocated directly to an old or tenured generation ? if it is, then on which bases ?

Answer 1

See “Frequently Asked Questions about Garbage Collection in the HotspotTM JavaTM Virtual Machine“:

Do objects ever get allocated directly into the old generation?

In 1.4.1 there two situations where allocation may occur directly into
the old generation.

If an allocation fails in the young generation and the object is a
large array that does not contain any references to objects, it can be
allocated directly into the old generation. In some select instances,
this strategy was intended to avoid a collection of the young
generation by allocating from the old generation.

There is a flag (available in 1.4.2 and later)
l-XX:PretenureSizeThreshold= that can be set to limit the
size of allocations in the young generation. Any allocation larger
than this will not be attempted in the young generation and so will be
allocated out of the old generation.

The threshold size for 1) is 64k words. The default size for
PretenureSizeThreshold is 0 which says that any size can be allocated
in the young generation.

In 1.4.2 case 1) the 64k word threshold continues to be true for the
incremental collector (-Xincgc). For the default collector and the
concurrent collector (-XX:+UseConcMarkSweepGC) the threshold value has
been changed so that an attempt to allocate into the old generation
only occurs if the size of the allocation is larger than the entire
young generation (available space when it is empty). It was observed
that there were cases where the 1.4.1 strategy for the default
collector and concurrent collector were leading to full collections
only (no young generation collections were being done). We deemed that
bad enough to raise the threshold.