Vb.net iii

ArguS academy V.B-PART-III

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Exception Handling An exception is a response to an abnormal or unexpected condition occurring in a program in a program, due to which the execution of a program may be aborted. To avoid the abrupt termination of the program, the exception is generally “caught” and “handled” appropriately. Code is written such that in case an exception occurred, alternative action is taken instead of aborting the program abruptly.

VB.Net used a structured mechanism to handle exceptions- the try …catch…end try block.

Module mtry Sub main() Dim a as integer=9 Dim b as integer

Dim c as integer Try c=a/b System.Console.WriteLine(c) Catch s as System.Exception System.Console.WriteLine(“Error ….divide by zero”) End try

End sub End module

When keyword Module mtry1 Sub main() Dim a as short Dim b as short Dim c as decimal System.Console.WriteLine(“Enter values of a and b”) a=System.Console.ReadLine() b= System.Console.ReadLine() try c=a/b System.Console.WriteLine(c) Catch s as System.Exception when b=0 System.Console.WriteLine(“Error…..divide by zero”) Finally System.Console.WriteLine(“End of main”) End try End sub End module

Multiple catch block There can be multiple catch blocks in one Try…End Try block. The order in which these catch statements are placed is very important. If a catch with a generic exception is placed right at the beginning followed by specific exception handlers, the specific exception handlers will never be executed as the generic exception handler will be executed first.

Option Strict on Module trym Sub main() Dim a as short Dim b as long a=5000 b=50000 try a=CType(b,Short) System.Console.WriteLine(a) Catch s as System.OverflowException System.Console.WriteLine(“Error…..value exceeds range of short”) Catch s as System.Exception System.Console.WriteLine(“Exception Occured”) System.Console.WriteLine(s) End try End sub End module


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Finally The finally Keyword is optionally used with the Try ….Ent try Block when an action when an action has to be carried out regardless of whether an exception occurred or not. If the exception occurs, the control is transferred to the catch block wherein the statements enclosed within are executed. The control is then passed onto the finally statement.

Module trym12

Sub main() Dim a as integer Dim b as integer Dim c as integer System.Controle.WriteLine(“Enter value of a and b”) a=System.Console.ReadLine() b=System.Console.ReadLine() try c=a/b System.Console.WriteLine(c) Catch s as System.Exception System.Console.WriteLine(“Error…divide by zero”) Finally System.Console.WriteLine(“End of main”) End Try End sub End module

Enumeration Enumeration are used when we need to refer to values of primitive types such as byte, short, integer and long as constants or literals

Module m1 Enum cities as short Ranchi Bokaro Dhanbad Jamshed Pur End Enum Sub main() System.Console.WriteLine(cities.Dhanbad) End sub End module

E.g.-ii Enum Grade as Byte A=100 B=80 C=70 D=60 E=40 End Enum Module m12 Sub main() Dim gradevalue as byte System.Console.WriteLine(“Choose one of the values: 40/60/70/80/100”) Gradevalue=System.Console.ReadLine() Select case gradevalue Case grade.A System.Console.WriteLine(“You got an A”) Case grade.B System.Console.WriteLine(“You got an B”) Case grade.C System.Console.WriteLine(“You got an C”) Case grade.D System.Console.WriteLine(“You got an D”) Case grade.E


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System.Console.WriteLine(“You got an E”) Case Else System.Console.WriteLine(“Wrong Choice”) End select End sub End Module

Structure A structure is a composite user-defined data type using which we can group data of different data types together. A structure is useful when we wish to create a record-like structure for an entity. A structure can hold not only fields but also methods, properties and events.

Module m12 Public structure book Public title as string Public author as string Public pages as integer Public price as single End structure Sub main() Dim b as new book() System.Console.WriteLine(“Enter Book Title”) b.title=System.Console.ReadLine() System.Console.WriteLine(“Enter Author Name”) b.author=System.Console.ReadLine() System.Console.WriteLine(“Enter Page”) b.page=System.Console.ReadLine() System.Console.WriteLine(“Enter Price”) b.price=System.Console.ReadLine() System.Console.WriteLine(“Book Title ”&b.title) System.Console.WriteLine(“Author Name “&b.author) System.Console.WriteLine(“Page “&b.page) System.Console.WriteLine(“Price “&b.price) Ens sub End module

Array within structures

Module m123 Public structure x Public arr() as integer End structure Sub main() Dim obj as x Redim obj.arr(1) obj.arr(0)=155 obj.arr(1)=200 System.Console.WriteLine(“1

st Values ”& obj.arr(0))

System.Console.WrteLine(“2nd

Values ”& obj.arr(1)) End sub End module

Procedures within Structure In addition to data members, a structure can also define functions and procedures within its declaration Module m123 Structure stud Public name as string Public rollno as integer Public sub accept()


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System.Console.WriteLine(“Enter Name”) name=System.Console.ReadLine() System.Console.WriteLine(“Enter Roll No”) rollno=System.Console.ReadLine() end sub end structure sub main() dim s as stud s.accept() System.Console.WriteLine(“The student details are”) System.Console.WriteLine(“Name ” & s.name) System.Console.WriteLine(“Roll No ” &s.rollno) End sub End Module

Structure within structure

A structure can be declared within another structure. This can be useful when a structure contains a composite data type as it member.

Module m321 Structure dateofbirth Public day as integer Public month as integer Public year as integer End structure Structure stud Public name as String Public rollno as integer Public dob as dateofbirth Public sub accept() System.Console.WriteLine(“enter name”) name=System.Console.readLine() System.Console.WriteLine(“enter roll no”) rollno=System.Console.readLine() end sub public void acceptdob() System.Console.WriteLine(“enter day”) dob.day=System.Console.readLine() System.Console.WriteLine(“enter month”) dob.month=System.Console.readLine() System.Console.WriteLine(“enter year”) dob.year=System.Console.readLine() end sub end structure sub main() dim s as stud s.accept() s.acceptdob() System.Console.WriteLine(“The Student details are”) System.Console.WriteLine(“Student Name ”& s.name) System.Console.WriteLine(“Roll No ” &s.rollno) System.Console.WriteLine(“Date ” & s.dob.day & ”/”) System.Console.WriteLine(“Month ” & s.dob.month & ”/”) System.Console.WriteLine(“Year ” & s.dob.year & ”/”) End sub End module

Object oriented programming Object oriented programming (oop) is based on a real world interpretation of programming elements. It is a type of programming in which programmers define not only the data elements but also the operations that can be performed on the data elements. An object is an entity consisting of data as well as actions.


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Object oriented programming are analogous to real words object and define not only the data elements but also define operation that may be applied to the elements. An object can have attributes and operations. Public class vehicle Public companyname as string Public price as integer Public mileage as integer End class Public sub mian() Dim car as new vehicle Dim truck as new vehicle System.Console.WriteLine(“Enter car company name ”) car.companyname=System.Console.readLine() System.Console.WriteLine(“Enter car price ”) car.price=System.Console.readLine() System.Console.WriteLine(“Enter car mileage”) car.mileage=System.Console.readLine() System.Console.WriteLine(“Enter truck company name ”) truck.companyname=System.Console.readLine() System.Console.WriteLine(“Enter truck price ”) truck.price=System.Console.readLine() System.Console.WriteLine(“Enter truck mileage”) truck.mileage=System.Console.readLine() end sub end module

Methods Methods govern the behaviour of the object. Methods in a class typically consist of action statements similar to a function or a procedure and are written using a sub main()…. End sub block

Module m145 Public class data1 Public a as integer Public b as integer Public c as integer Public sub getdata() System.Console.WriteLine(“Enter two no”) a=System.Console.ReadLine() b=System.Console.ReadLine() c=a+b end sub end class public sub main() dim ob as new data1 ob.getdata() System.Console.WriteLine(“Value of A =” & ob.a) System.Console.WriteLine(“value of B= ” & ob.b) System.Console.WriteLine(“sum of A & B = ” & ob.c) End sub End module

e. g. ii Module m111 Public name as String Public gender as char Private age as integer Public address as String Public property agevalue() as integer Set(ByVal value as integer) age=value end set


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get return age end get end property public sub input() System.Console.WriteLine(“Enter the name, gender and address”) name=System.Console.ReadLine() gender= System.Console.ReadLine() address= System.Console.ReadLine() end sub end class public sub main() dim student as new person student.age=19

student.input() System.Console.writeLine() System.Console.writeLine(“Student details are ”) System.Console.writeLine() System.Console.writeLine(“Student Name ” & student.name) System.Console.writeLine(“Student Gender ” & student.gender) System.Console.writeLine(“Student Age ” & student.age) System.Console.writeLine(“Student Address ” & student.address)

End sub End module

Constructor and Destructors A constructor is a method having the same name as the class within which it is defined. This method executes automatically every time an object is created. Constructor are typically declared public and are used for initialization purposes. Destructors are methods that execute whenever the object goes out of scope or is destroyed.

Constructors In VB. Net, the lifetime of an object begins when it is created with the New keywords. Constructors in VB. Net are written using the sub New() … end Sub block Module mcon Public class point Public x as integer Public y as integer Public sub New() System.Console.WriteLine(“This is a Constructor”) System.Console.WriteLine(“Enter values for point”) x= System.Console.ReadLine() y= System.Console.ReadLine() end sub end class public sub main() dim p as new point() System.Console.WriteLine(“Point p is”) System.Console.WriteLine(“Value of x= ” & p.x) System.Console.WriteLine(“Value of y= ” & p.y) End sub End module

Destructors Module mdes Public class point Public x as integer Public y as integer Public sub new() System.Console.WriteLine(“This is a constructor”) System.Console.WriteLine(“Enter values for point”) x= System.Console.ReadLine()


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y= System.Console.ReadLine() end sub overrides protected sub finalize() System.Console.WriteLine(“This is a destructor executing since object is now going to be destroyed”)

End sub End class Public sub main() Dim p as new point() System.Console.WriteLine(“Point p is ”) System.Console.WriteLine(p.x) System.Console.WriteLine(p.x) End sub End module

Overloading, Inheritance and overriding

Overloading is the process of declaring method of a class having the same name but different signatures. The signature of a method comprises of the name of the method, the number and type of arguments. The return type of a method is not a part of the signature and hence cannot be used as a factor for overloading. The overloads keyword indicates that the method or property is being overloaded. It is not mandatory to use the overloads keyword. However, once it is used with a method all subsequent overloaded methods must use it.

Procedure and function Overloading Module m121 Class x Sub max(a as integer, b as integer) Dim c as integer c=a+b System.Console.WriteLine(“Sum of a and b is ” & c) End sub Sub max(s1 as String, s2 as String) Dim s3 as String s3=s1+s2 System.Console.WriteLine(“the combined string is ” & s3) End sub End class Sub main() Dim y as new x() y.max(10,15) y.max(“Argus”, “Academy”) end sub end module

Constructor overloading is a special case of method overloading. Parameterized constructors that satisfy the rule for overloading can be used within classes.

Module m1234 Class base Public sub new() System.Console.WriteLine(“Parameterless constructor ”) End sub Public sub new(x as integer) System.Console.WriteLine(“integer parameter constructor ”) End sub Public sub new( s as String) System.Console.WriteLine(“String parameter constructor ”) End sub End class

Sub main() Dim b1 as new base() Dim b2 as new base() Dim b3 as new base(“Hello”) End sub


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End module

Property Overloading Just as procedures and function can be overloaded, properties within a class too can be overloaded.

Module m1 Public class x Private addr as string Private addr2 as sting Overloads public property address() as string Set(Byval add as String) addr=add end set get return addr end get end property overloads public property Address (s as string) as string set (Byval add as string) addr2=add end set get return addr2 end get end property end class public sub main() Dim y as new x() Dim s as String System.Console.WriteLine(“Enter Company Address”) y.address()=System.Console.ReadLine() System.Console.WriteLine(“Enter residence address”) y.address(“residence”)=System.Console.ReadLine() System.Console.Writeline(“the residence Address is :”) System.Console.Writeline(y.address(“residence”)) System.Console.Writeline(“the Company Address is :”) System.Console.Writeline(y.address()) End sub End module

Inheritance Inheritance is the process of creating classes based on existing classes. Inheritance is based on the principle of code reuse. Instead of creating a class from scratch, we can add new methods, properties, and events to existing classes, thus saving time and effort. The class based on which the new class is created is called base class or parent class and the class that is created is called derived or child class.

Access Modifiers and inheritance

With respect to inheritance, access modifiers play a very importance role. In VB. Net, there are five access modifiers that are relevant to inheritance : Public, private, protected, Friends and protected friend

- All public elements of a class are inherited by its derived classes. - Private elements of a class cannot be inherited by derived class. - Protected access for elements denotes that elements may be used within the derived class but not outside the derive

class. - Friend access modifier is used to denote that the element is accessible throughout the program in which the class is

defined. - Protected Friend access modifier indicates that the elements bears features of both protected and friend modifiers.

Module m123 Public class x Public j as integer


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Private k as integer Protected l as integer Friend m as integer Public sub test() l=100 end sub end class public class y Inherits x Public n as integer End class Public sub main() Dim a as new x() Dim b as new y() a.j=100 a.m=100 a.test() b.j=120 b.m=130 b.test() b.n=150 System.Console.WriteLine(“Value of j in base class ” & a.j) System.Console.WriteLine(“Value of m in base class ” & a.m) System.Console.WriteLine(“Value of j in derive class ” & b.j) System.Console.WriteLine(“Value of m in derive class ” & b.m) System.Console.WriteLine(“Value of n in derive class ” & b.n) End sub End module

Inheriting Constructor and destructor Constructor and destructors are by default, inherited by derived classes. Module m1 Class base Public sub new() System.Console.WriteLine(“Constructor of Base class”) End sub End class Class child Inherits base End class Sub main() Dim b as new base() System.Console.WriteLine(“Now creating child class object”) Dim c as new child() End sub End module

Destructor is inherited by a derived class

Module md Class base Public sub new() System.Console.WriteLine(“Constructor of Base class”) End sub Overrides protected sub Finalize() System.Console.WriteLine(“Destructor of Base Class”) End sub End class Class child Inherits base End class


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Sub main() Dim b as new base() System.Console.WriteLine(“Now creating child class object”) Dim c as new child() End sub End module

Abstract Classes An abstract class is a class that cannot be instantiated. In other words, an abstract class cannot be used to create objects. It is generally used as a template to derive other classes. An abstract class typically has abstract methods which are only method declaration without any implementation. Module m1 MustInherit class absbase Public sub test() System.Console.WriteLine(“Abstract Base Class”) End sub MustOverride Sub AnotherTest() End class Class child Inherits absbase Overrides sub AnotherTest() System.Console.WriteLine(“Implementing abstract method”) End sub End class Sub main() Dim c as new child() c.test() c.AnotherTest() end sub end molude

Final classes Final classes in VB.Net are market with the NotInheritable keyword. Final classes cannot have derived classes but can be used to create objects.

Module m1 NotInheritable class one Public sub test() End sub Public sub test(x as integer) System.Console.WriteLine(“value is ” & x) End sub End class Sub main() Dim f as new one() f.test() f.test(100) end sub end module

Overriding Overriding is the process of overwriting the methods or properties of a base class in a derived class. In case of method overriding, the return type, name and arguments of the method in the derived class must be the same as that of the method being overridden. When an object of the derived class invokes the overridden method, it will be the derived class implementation that will be called. The base class method must be marked with the keyword Overridable and the derived class method must be marked with the keyword Overrides.

Module m12 Class base Overridable public sub test(a as integer, b as integer) System.Console.WriteLine(“Answer is ” & a+b) End sub End class


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Class child Inherits base Overrides public sub test(a as integer, b as integer) System.Console.writeLine(“Answer is ” & a*b) End sub End class Sub main() Dim b as new base() Dim c as new child() b.test(10,20) c.test(10,20) end sub end module

Shadows keyword

If we wish to hide an inherited methods within a derived class, and invoke an overridden version of the method, then we use the shadows keyword cannot be used with the overloads keywords.

Module m12 Class base Public sub test() Public sub test() End sub Public sub test(x as integer) System.Console.writeLine(“ value from base class ” & x) End sub End class Class child Inherits base Shadows sub test(y as integer) System.Console.writeLine(“value from child class ” & y) End sub End class Sub main() Dim c as new child() c.test(100) end sub end module

MyBase Keyword

This keyword is used to refer to the base class method in a derived class that has overridden methods of the base clasystem.s MyBase cannot act as a variable nor does it contain any value that can be passed or assigned. MyBase refer to the immediate base class and its inherited members. It can be used to access only public and protected members of the base class.

Module m12 Public class animal Overridable public sub eats() System.Console.WriteLine(“Eats Food”) End sub End class Public class cow Inherits animal Overrides public sub eats() System.Console.WriteLine(“Eats grass”) End sub Public sub eating() MyBase.eats() System.Console.WriteLine(“is a herbivorous animal ”) End sub End class Sub main() Dim a as new animal() Dim c as new cow() c.eating()


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c.eats() end sub end module

MyClass keyword

This keyword opposite to the way in which MyBase keyword works. Assume that a base class method is overridden in a derived class. If the object that is used to invoke the method is of type derived class.

Module m12 Public class animal Overridable public sub eats() Systen.console.WriteLine(“Animal eats food”) End sub Public sub eatinghabits() System.Console.WriteLine(“Calling method directly”) Eats() System.Console.WriteLine(“Calling method using myclass”) Myclass.eats() End sub End class Public class cow Inherits Animal Overrides public sub eats() System.Console.WriteLine(“Cow eats grass”) End sub End class Sub main() Dim c as new cow() c.eats() c.eatinghabits() end sub end module

Interfaces, Namespaces and Collection

Interface Interfaces are similar to classes except that they have no implementation. Methods are only declared within an interface and do not contain any code. An interface cannot be instantiated. It is typically implemented by a class using the implements keyword. An interface is defined using the interface …. End interface keywords .

Module m12 Public interface I Sub First() Sub Second() End Interface Public class x Implements I Sub First() Implements I.First System.Console.WriteLine(“Implementation of first method”) End sub Sub Second() Implements I.Second System.WriteLine(“Implementation of second method”) End sub End class Public sub main() Dim y as new x() y.First() y.Second() end sub end module

Multiple Inheritance

Module m1 Public Interface I Sub test() End Interface


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Public class T Public Sub Testing() System.Console.WriteLine(“Method Testing”) End sub End class Public class x Inherits T Implements I Sub Test() Implements I.Test System.Console.WriteLine(“Implemented method”) End sub End class Public sub main() Dim y as new x() y.test() y.testting() end sub end module

Namespaces

In VB. Net class libraries are comprised of namespaces. Namespace are used to organize nested entities such as other namespace, classes, interfaces and so on. Namespace take care of the way in which program elements are exposed to other programs with the help of various access modifiers. Modules and classes are generally put inside namespaces. A namespace declaration consists of the keyword Namespace followed by a qualified identifier that servers as the namespace name. Optional namespace member declarations as enclosed between Namespace and End Namespace keywords.

Namespace plants public class abc public fname as String public lname as String public sub print() System.Console.WriteLine("First name " & fname) System.Console.WriteLine("Last Name " & lname) end sub end class end Namespace save this file filename.vb module m1 sub main() dim s as new plants.abc System.Console.WriteLine("Enter first name") s.fname=System.Console.ReadLine() System.Console.WriteLine("Enter Last name") s.lname=System.Console.ReadLine() s.print() end sub end module Save this file –test.vb The option /t: library is include with the vbc command to compile a .vb file to a dll file.


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Example 2 Imports plants Module m1 Sub main() Dim s as new String s.fname=”Argus” s.fname=”Academy” s.print() end sub end module

Collection

A collection is a term used to describe a means of grouping and managing related entities. In VB.Net, a collection is used to manage object that are exposed by a class. The simplest way to do this is to create a public instance of type

System.Collection.ICollection- This interface provides a count() method that counts the total number of items in a collection. It also provides additional methods for advanced operations like multithreading.

System.Collection.IEnumerable- This interface exposes an object that implements IEnumeration interface. This is used whenever a collection contains objects.

System.Collections.IList-this interface provides list type access to a collection. It provides methods to add, remove and search for items or objects in a collection.

Module m1 Public class book Public title as string Public author as string Public sub new() System.Console.WriteLine(“Enter Book Title”) title=System.Console.ReadLine() System.Console.WriteLine(“Enter Author Name”) author=System.Console.ReadLine() end sub end module public bookCollection as new Microsoft.VisualBasic.Collection public sub main() dim b as new book() dim c as new book() dim d as new book() bookCollection.Add(b) bookCollection.Add(c) bookCollection.Add(d) dim i as integer System.Console.WriteLine() System.Console.WriteLine(“list of Book Titles: ”) Syste.Console.WriteLine() For I to bookCollection.count() System.Console.WriteLine(bookCollection.item(i).title()) next end sub end module

The Code declares a class called Book having Title and Author as its data members and a construction method which reads in values for these data members from the used.

Strongly typed Collection

With a simple non-typed collection, any object can be added to the collection. Since it may not be possible to implicitly convert the element type of the collection to the type of the collection to the type of the iteration value, this feature can cause problems later at runtime if we use a for….each loop to iterate through the collection. The for .. each next loop is used with array or collections. The statements within the loop are executed for each element within the array or collection until all the elements have been iterated


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Module m1 Enum Color Amber Purple Tan Blue Black Grey Whyte End Enum Public class colorCollection Inherits System.Collections.CollectionBase Public function add(ByVal col As Color ) As Integer MyBase.List.Add(col) End function Public sub insert(ByVal I as Integer, ByVal c as Color) List.Insert(I,c) End sub Public sub Remove (ByVal c as Color) List.Remove(c) End Default property item(ByVal I as Integer ) As Color Get Return CType(MyBase.List(i),Color) End get Set(ByVal c as Color) myBase.List.Item(i)=c end set end property end class sub main() dim col as new ColorCollection() col.Add(Color.Amber) col.Add(Color.Purple) col.Add(Color.Tan) col.Add(Color.Blue) col.Add(Color.Black) col.Add(Color.Grey) col.Add(Color.White) dim shade as Color for each Shade in col System.Console.WriteLine(shade.ToString) Next Shade =col(1) System.Console.WriteLine(“shade ” & shade.ToString) System.Console.WriteLine() Try Dim n as integer =col.count() System.Console.WriteLine(“Last item added to the collection is ” & col.item(n-1).ToString()) Col.add(“just some text”) Catch e as System.Exception System.Console.WriteLine(e.Message) End try End sub End module


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Assignments Structure Exception Handling

1. WAP to store information of 10 employees and to display information of an employee depending upon the employee no 2. WAP to accept 5 students marks from user and print the students result using structure array inside it. 3. Write a program to accept 2 numbers from the user and calculates their product. Appropriate exception handling code

must be written to take care if the product of the two numbers is very large and does not fit into the data type.

Assignments Class & Object constructor

1. WAP class name student, data member String name, integer rollno, double m1,m2,m3, total, per Member function sub getdata()- accept the name, rollno, and 3 marks from user. Sub calculate()- Calculate the total and percentage. Sub display()- display all the information and grade, grade depends on percentage Per>=95 – Grade A* Per>=80 and per<95 – Grade A Per>=70 and per<80 Grade B* Per>=60 and per<70 Grade B Per>=50 and per<60 Grade C Per>=33 and per< 50 PASS

2. WAP class name counter, data member : integer count Member function: Init() function that initializes count to 0 Inccount() increment count by 1 Givecount() returns the value of count Design a program use this class counter to count the number of ladies, the number of gentlemen and the number of children in a guest list. The guest list is stored as a character type array guest(). It consists of the following codes Code stands for G gentleman L lady C child

3. Declare a class to represent bank account of 10 customers with the following data member : name of depositor, Account Number, type of account (s for savings and c for current account), Balance amount. The class also contains following member functions:

- To initialise data members. - To deposit money - For withdrawal of money after checking the minimum balance (minimum balance is Rs. 1000) - To display the data member.

Assignments Inheritance

1. WAP to read and display information about employees and managers. Employee is the base class and Manager is the sub class

2. WAP to display the area of circle, area of rectangle and area of cylinder all variable will be declared in super class by using the inheritance.

3. Write a program to declare a class student. This class should have two derived classes graduate and undergraduate. The class student should have a method test() that should print a message “This is a student ”. This method should be overridden in the derived classes to print the messages “this is graduate” and “This is undergraduate” respectively . write the code such that in the main block, first only “this is a student ” is displayed no matter which Test() method is invoked.

4. Write a program that will create a namespace N with a class X having three integer members A,B and C. these members are declared public. Make use of this namespace N and X in another namespace M having a class Y. this program should assign the values 100,200 and 300 to the three integer members of class X. Finally display the sum of the three integer variables

Education

Vb.net iii