Question 16 :
What is a transient variable?
A transient variable is a variable that may not be serialized.
Question 17 :
Which containers use a border Layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default layout.
Question 18 :
Why do threads block on I/O?
Threads block on I/O (that is enters the waiting state) so that other threads may execute while the I/O Operation is performed.
Question 19 :
What is the output from System.out.println("Hello"+null);?
Question 20 :
What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.