Java Interview Questions 32

156. How are Observer and Observable used?
Answer: Objects that subclass the Observable class maintain a list of observers.
When an Observable object is updated it invokes the update() method of each of its
observers to notify the observers that it has changed state. The Observer interface
is implemented by objects that observe Observable objects.

157. What is synchronization and why is it important?
Answer: 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 causes dirty data and leads to significant errors.

158. What are synchronized methods and synchronized statements?
Answer: Synchronized methods are methods that are used to control access to an
object. A thread only executes a synchronized method after it has acquired the lock
for the method's object or class. Synchronized statements are similar to
synchronized methods. A synchronized statement can only be executed after a thread
has acquired the lock for the object or class referenced in the synchronized
statement.

159. How are Observer and Observable used?
Answer: Objects that subclass the Observable class maintain a list of observers.
When an Observable object is updated it invokes the update() method of each of its
observers to notify the observers that it has changed state. The Observer interface
is implemented by objects that observe Observable objects.

160. What is synchronization and why is it important?
Answer: 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 causes dirty data and leads to significant errors.