Virtual method has an implementation & provide the derived class with the option of overriding it.

Abstract method does not provide an implementation & forces the derived class to override the method.

1. Positive test cases (correct data, correct output).

2. Negative test cases (broken or missing data, proper handling).

3. Exception test cases (exceptions are thrown and caught properly).

System.Diagnostics.Process objDocProcess = new System.Diagnostics.Process();

objDocProcess.EnableRaisingEvents = false;

objDocProcess.StartInfo.FileName = @"C:\Excel.xls";

A string is a sequential collection of Unicode characters that is used to represent text. At the other hand the string builder is sealed class(Cannot be inherited)it represents a mutable string of characters.

String is mutable that means that it can't be modified once created, to modify a given string by appending new characters or so the CLR destroy the first string instance and create a new string one and this costs in terms of memory and time process.

 Using the string builder, you create a mutable object that recieves modification without having to be destroyed and reinstanciated for each modifiaction

Poly means many and morph means form. Thus, polymorphism refers to being able to use many forms of a type without regard to the details.

Polymorphism have 2 types :

1. Compile time also called overloading have 3 types.

·         Constructor overloading (i.e., with same constructor name and different no of arguments or different datat types or both )

·         Function overloading (i.e., with same function name and different no of arguments or different data types or both)

·         operator overloading: example : Variable++;

2 Run time

·         It is achieved by overriding parent class method: