Java Interview Questions page 3
Question: How many methods in the Serializable interface?
Answer:There is no method in the Serializable interface. The
Serializable interface acts as a marker, telling the object
serialization tools that your class is serializable.
Question: . How many methods in the Externalizable interface?
Answer: There are two
methods in the Externalizable interface. You have to implement these two
methods in order to make your class externalizable. These two methods are
readExternal() and writeExternal().
Question: What is the difference between Serializalble and Externalizable
interface?
Answer: When you use Serializable interface, your class is serialized
automatically by default. But you can override writeObject() and readObject()
two methods to control more complex object serailization process. When you
use Externalizable interface, you have a complete control over your class's
serialization process.
Question: What is a transient variable?
Answer: A transient variable is a variable that
may not be serialized. If you don't want some field to be serialized, you
can mark that field transient or static.
Question: Which containers use a border layout as their default layout?
Answer: The
Window, Frame and Dialog classes use a border layout as their default
layout.
Question: . 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.
Question: 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.
Question: 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.
Question: 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.
Question: 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.