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IN java collections we have both interfaces and classes.
instead of using interfaces why we can't use classes only
like that why we can't use interfaces only. why we need two
things interface and class.
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Answer Posted / shaik baji
Interface in the sence a generic templet that means it will
define a generic functionalities of a group.
For Ex:- We can say "Car" as an interface
1)let's asume if you want a List interface functionalities
the your class should implements the List interface, that
means you should implement all the methods which are
available in List interface even you are not using all the
methods so that the Java developers designed the classes
which are implements the java.util interfaces.
Now if you want any interface functionalities then you just
create an object of that related java.utill package class
and call the methods by using the object.
2)Java doesn't support multiple inheritance.We achieve
multiple inheritance using interface concept.A class can
have only one super class and number of interface.
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The following program reads data (details of students) from a file named students.txt and converts it into e-mail addresses. The results are written to a file named studentemail.txt. students.txt consists of a number of lines, each containing the data of a student in colon delimited format: Last Name:First Name:Student Number Each input record is converted to an e-mail address and written to studentemail.txt in the following format: the first character of the last name + the first character of the first name + the last four digits of the student number + “@myunisa.ac.za” import java.io.*; public class EmailConverter { public static void main(String[] args) throws IOException { BufferedReader input = new BufferedReader(new FileReader ("students.txt")); PrintWriter output = new PrintWriter(new FileWriter ("studentemail.txt")); String line = input.readLine(); while (line != null) { // Extract the information for each student String[] items = line.split(":"); // Generate the email address String email = "" + items[0].charAt(0) + items[1].charAt(0) + items[2].substring(4,8) + "@myunisa.ac.za"; email = email.toLowerCase(); // Output output.println(email); line = input.readLine(); } input.close(); output.close(); } } Rewrite the class so that it handles possible errors that may occur. In particular, it should do the following: • It should catch at least three appropriate exceptions that might occur, and display suitable messages. • At this stage, the program will not run correctly if there is an empty line in the input file. Change the program so that if an empty line is encountered, an exception is thrown and the empty line is ignored. This exception should be handled with the display of a suitable error message. • Before the e-mail address is added to the output file, check if the student number has 8 digits. If not, throw an InvalidFormatException (which the program should not handle itself)
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