What is abstraction with strong example program?
(not a general program)
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Answer Posted / gaurav (accenture)
Just to tell you guys that abstraction and encapsulation are two different concepts of oops. thats why they've use two terminologies. Common Sense. Right.!
The meaning of abstraction is just the same as it is in English but applying it in coding world. Simply we can say as “what” the method or a module does not “how” it does it. The word abstraction is to distill a complicated system down to its most fundamental parts and describe these parts in a simple, precise language.
Let’s compare Java and C++. We have a good example of abstraction. In C++, you have to deal with pointers and references a lot. You have to deal a lot of garbage collection. In essence, you have to work on a low level. (C and C++ in turn abstracted a lot of even lower level machine code.) In Java, those things are abstracted away. You just assume they exist. In essence, abstraction means that you are working on a higher level. You don’t care how pointers work in Java, you just assume that they work. You don’t have to concentrate on the lower level stuff, you work on higher level.
I hope it covers everything.
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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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