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Question 6 :

If a class is located in a package, what do you need to change in the OS environment to be able to use it?

Answer :

You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:

c:\>java com.xyz.hr.Employee

 


Question 7 :

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 8 :

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 9 :

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 10 :

What is a transient variable in Java?

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.