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Core Java Interview Questions and Answers

Ques 11. Explain the usage of Java packages.

Ans. 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.

java.lang basic language functionality and fundamental types
java.util collection data structure classes file operations
java.math multiprecision arithmetics
java.nio the New I/O framework for Java networking operations, sockets, DNS lookups 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 12. If a class is located in a package, what do you need to change in the OS environment to be able to use it?
Ans. 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; and is located in the file c:/dev/ 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:
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Ques 13. What's the difference between J2SDK 1.5 and J2SDK 5.0?
Ans. There's no difference, Sun Microsystems just re-branded this version.
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Ques 14. What would you use to compare two String variables - the operator == or the method equals()?
Ans. I would use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.
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Ques 15. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?
Ans. Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses have to be caught first.
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