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Core Java Interview Questions and Answers

Ques 186. What restrictions are placed on the location of a package statement within a source code file?

A package statement must appear as the first line in a source code file (excluding blank lines and comments).

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Ques 187. Which package is always imported by default?

The java.lang package is always imported by default.

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Ques 188. What is a package?

To group set of classes into a single unit is known as packaging. Packages provides wide namespace ability.

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Ques 189. Explain the usage of Java packages.

This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.

e.g.
java.lang basic language functionality and fundamental types
java.util collection data structure classes
java.io file operations
java.math multiprecision arithmetics
java.nio the New I/O framework for Java
java.net networking operations, sockets, DNS lookups
java.security key generation, encryption and decryption
java.sql Java Database Connectivity (JDBC) to access databases
java.awt basic hierarchy of packages for native GUI components
javax.swing hierarchy of packages for platform-independent rich GUI components
java.applet classes for creating an applet

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Ques 190. If a class is located in a package, what do you need to change in the OS environment to be able to use it?

You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Lets 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

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