Question 16 :
How do you know if an explicit object casting is needed?
If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:
Object a; Customer b; b = (Customer) a;
When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
Question 17 :
What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
Question 18 :
How do you restrict a user to cut and paste from the html page?
Using Servlet or client side scripts to lock keyboard keys. It is one of solutions.
Question 19 :
What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
Question 20 :
What is Serialization and deserialization ?
Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.