12. What is the difference
between optimistic lock and pessimistic
lock?
Optimistic lock
is an implicit lock that tries to make best assumption about locking
strategy and minimize time spent in lock of resource. Optimistic lock is
usually implemented with some kind of timestamp strategy. Pessimistic
lock is an explicit lock that set by
client.
13.
Is null a
reserved word in Java? Can you declare a variable with a name of
null?
Yes, null is a
reserved word in Java, we cannot declare null as a variable
name.
14.
What is the
word transient?
Transient means
that the value of this member variable does not have to be serialized
with the object.
15.
When do you
need explicit casting of objects?
If we assign a
superclass to a variable of subclass data type then we need to cast that
object.
16.
What is the
method sleep()? How is it different from
wait()?
The code
sleep(1000);