Constructor

1. What is a Constructor in C#?

A constructor is a special method that runs when an object of a class is created. It initializes the object and allocates memory. The constructor has the same name as the class and does not have a return type.

Key Points:

• Same name as the class.
• No return type, not even void.
• Can have parameters.
• Can have access modifiers.
• Cannot return a value, but can use return;.

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2. Can we define a method with the same name as the class in C#?

No, you cannot have a method with the same name as the class. It will result in a compile-time error.

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3. How many types of constructors are there in C#?

• Default Constructor
• Parameterized Constructor
• Copy Constructor
• Static Constructor
• Private Constructor

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4. What is a Default Constructor?

A default constructor has no parameters. It can be:

• System-defined: Automatically provided by C#.
• User-defined: Explicitly created by the developer.

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5. When should we define a Parameterized Constructor?

Use a parameterized constructor when you want to initialize an object with specific values provided by the user.

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6. What is a Parameterized Constructor?

A parameterized constructor allows you to set different values for each instance of a class. This way, you can create objects with distinct initial values.

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7. How many constructors can be defined in a class?

You can define multiple constructors in a class as long as they have different parameter types or orders. This includes one default constructor and any number of parameterized constructors.

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8. What is a Copy Constructor in C#?

A copy constructor takes an object of the same class as a parameter and initializes a new object with the values from that existing object.

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9. Explain the Static Constructor in C#.

A static constructor is called once, regardless of how many instances of the class are created. It's used to initialize static fields and cannot have parameters or access modifiers.

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10. What is a Private Constructor in C#?

A private constructor restricts object creation from outside the class. It's often used in design patterns like Singleton, ensuring only one instance of the class exists.

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11. When is a Destructor called?

A destructor is called automatically when an object is destroyed, usually by the garbage collector.

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12. When does an object get destroyed?

An object can be destroyed when:

1. The program ends.
2. The garbage collector runs due to memory pressure.
3. You explicitly call GC.Collect().

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13. Can a child class call the constructor of a base class?

Yes, a child class can call a base class constructor using the base keyword.

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14. Which constructor is called first when a child class instance is created?

The base class constructor is called first, followed by the child class constructor.

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15. Can you mark a static constructor with access modifiers?

No, static constructors cannot have access modifiers.

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16. Can static constructors have parameters?

No, static constructors cannot accept parameters.

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17. Give two scenarios where static constructors can be useful.

• Initializing a log file for a class.
• Loading unmanaged code with LoadLibrary.

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18. What is a Destructor?

A destructor is a method that is called when an instance of a class is destroyed. It has the same name as the class, prefixed with a tilde (~).

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19. Can a class have more than one destructor?

No, a class can only have one destructor.

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20. Can you pass parameters to destructors?

No, destructors cannot take parameters and cannot be overloaded.

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21. Can you explicitly call a destructor?

No, destructors are automatically invoked by the garbage collector.

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22. When should you use a Private Constructor?

• To prevent instantiation from outside the class.
• To implement the Singleton design pattern.
• When some constructors should only be used internally.

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23. If a class has a parameterized constructor, do you need a default constructor?

If you have a parameterized constructor, you need to define a default constructor explicitly if you want one.

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24. Can constructors be inherited?

No, constructors cannot be inherited.

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25. How can you call a base class constructor from a child class?

You can call a base class constructor using the base keyword in the child class constructor.

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26. In which order are constructors called in inheritance?

When creating an object of a derived class, the base class constructor is called first, followed by the derived class constructor.

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27. Can constructors be overloaded?

Yes, constructors can be overloaded by varying parameters.

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28. How do you overload a constructor?

You overload a constructor by defining it with different parameter types or numbers.

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29. How do you call one constructor from another in the same class?

You can call one constructor from another using the this keyword.

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30. Which constructor is called first when you create an object of a class?

The first overloaded constructor is called, followed by the default constructor if it exists.

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31. Can a constructor call itself using the this keyword?

No, doing so will result in a compile-time error.

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32. Does memory get allocated when a constructor is called?

Yes, memory is allocated using the new operator when a constructor is invoked.

Programming Related Question Answers

 1. How to reverse a string?

string aa = "Hello World!";

string str = new string(aa.Reverse().ToArray());

                                    OR

string aa = "Hello World!";

var result = aa.ToCharArray().Reverse();

Console.WriteLine(new string(result.ToArray()));

                                    OR

internal static void ReverseString(string str) 

{ 

    char[] charArray = str.ToCharArray(); 

    for (int i = 0, j = str.Length - 1; i < j; i++, j--) 

    { 

        charArray[i] = str[j]; 

        charArray[j] = str[i]; 

    } 

    string reversedstring = new string(charArray); 

    Console.WriteLine(reversedstring); 

}

 

2. Prime number?

public static bool IsPrimeNumbers(int number) 

{ 

    bool returnMsg = false; 

    for (int i = 2; i <= number; i++) 

    { 

        if ((number % i) == 0 && number != i) 

        { 

            returnMsg = false; 

            return returnMsg; 

        } 

        else if (number == i) 

        { 

            returnMsg = true; 

            return returnMsg; 

        } 

    } 

    return returnMsg; 

} 

 

3. Fibonacci series?

public static void PrintFibonacciSeries(int limit) 

{ 

    int digit1, digit2, digit3; 

    digit1 = 0; 

    digit2 = 1; 

    digit3 = digit1 + digit2; 

    Console.WriteLine(digit1); 

    Console.WriteLine(digit2); 

    Console.WriteLine(digit3); 

    for (int i = 0; i < limit; i++) 

    { 

        digit1 = digit2; 

        digit2 = digit3; 

        digit3 = digit1 + digit2; 

        Console.WriteLine(digit3); 

    } 

} 

 

4. How to find if the given string is a palindrome or not?

public bool isPalindrome(string myString)

{

    string string1, rev;

    string1 = "Malayalam";

    char[] ch = string1.ToCharArray();

    Array.Reverse(ch);

    rev = new string(ch);

    bool b = string1.Equals(rev, StringComparison.OrdinalIgnoreCase);

    if (b == true)

    {

        Console.WriteLine("" + string1 + " is a Palindrome!");

    }

    else

    {

        Console.WriteLine(" " + string1 + " is not a Palindrome!");

    }

 

    return b;

}

 

5. Get Factorial of number.

public static int PrintFactorialOfNumber(int number) 

{ 

    // 5*4 

    int result = 1; 

    for (int i = number; i > 0; i--) 

    { 

        result = result * i; 

    } 

    return result; 

} 

 

6. How to remove duplicate characters from a string?

internal static void removeduplicate(string str) 

 { 

     string result = string.Empty; 

 

     for (int i = 0; i < str.Length; i++) 

     { 

         if (!result.Contains(str[i])) 

         { 

             result += str[i]; 

         } 

     } 

     Console.WriteLine(result); 

 }

7. Find third Max salary using LINQ?

List<Employee> employees = new List<Employee>()

            {

                new Employee { Id = 1, UserName = "Anil" , Salary = 5000},

                new Employee { Id = 2, UserName = "Sunil" , Salary = 6000},

                new Employee { Id = 3, UserName = "Lokesh" , Salary = 8000},

                new Employee { Id = 4, UserName = "Vinay" , Salary = 7000},

                new Employee { Id = 5, UserName = "Amit" , Salary = 8000},

                new Employee { Id = 6, UserName = "Lokesh" , Salary = 5500},

                new Employee { Id = 7, UserName = "Mahesh" , Salary = 7000}

            };

var emp = employees.GroupBy(e => e.Salary).OrderByDescending(g => g.Key).Skip(2).First();

8. Join in LINQ?

var query = from department in departments

    join employee in employees

   on department.ID equals employee.DepartmentID 

   select new { employee.Name, Department = department.Name };

9. Left Outer Join in LINQ?

var Ljoin  =    from emp in ListOfEmployees

join proj in ListOfProject

on emp.ProjectID equals proj.ProjectID into JoinedEmpDept

from proj in JoinedEmpDept.DefaultIfEmpty()

select new

{

EmployeeName = emp.Name,

ProjectName = proj != null ? proj.ProjectName : null

};

SQL Server Query Related Questions and Answers

1. Write an SQL query to print the first three characters of  FIRST_NAME from Worker table.

Select substring(FIRST_NAME,1,3) from Worker;

2. Write an SQL query to find the position of the alphabet (‘a’) in the first name column ‘Amitabh’ from Worker table.

Select INSTR(FIRST_NAME, BINARY'a') from Worker where FIRST_NAME = 'Amitabh';

3. Write an SQL query to print the FIRST_NAME from Worker table after replacing ‘a’ with ‘A’.

Select REPLACE(FIRST_NAME,'a','A') from Worker;

4. Write an SQL query to print details for Workers with the first name as “Vipul” and “Satish” from Worker table.

Select * from Worker where FIRST_NAME in ('Vipul','Satish');

5. Write an SQL query to print details of workers excluding first names, “Vipul” and “Satish” from Worker table.

Select * from Worker where FIRST_NAME not in ('Vipul','Satish');

6. Write an SQL query to print details of Workers with DEPARTMENT name as “Admin”.

Select * from Worker where DEPARTMENT like 'Admin%';

7. Write an SQL query to fetch the no. of workers for each department in the descending order.

SELECT DEPARTMENT, count(WORKER_ID) No_Of_Workers 

FROM worker 

GROUP BY DEPARTMENT 

ORDER BY No_Of_Workers DESC;

8. Write an SQL query to determine the nth (say n=5) highest salary from a table.

SELECT TOP 1 Salary

FROM (

 SELECT DISTINCT TOP n Salary

 FROM Worker 

 ORDER BY Salary DESC

 ) as temp

ORDER BY Salary ASC;

9. Write an SQL query to fetch nth max salaries from a table.

SELECT distinct Salary from worker a WHERE n >= (SELECT count(distinct Salary) from worker b WHERE a.Salary <= b.Salary) order by a.Salary desc;

10. Write an SQL query to show the second highest salary from a table.

Select max(Salary) from Worker 

where Salary not in (Select max(Salary) from Worker);

11. Write an SQL query to fetch the list of employees with the same salary.

Select distinct W.WORKER_ID, W.FIRST_NAME, W.Salary 

from Worker W, Worker W1 

where W.Salary = W1.Salary 

and W.WORKER_ID != W1.WORKER_ID;

12. Write an SQL query to fetch the first 50% records from a table.

SELECT * FROM WORKER

WHERE WORKER_ID <= (SELECT count(WORKER_ID)/2 from Worker);

13. Write an SQL query to fetch the departments that have less than five people in it.

SELECT DEPARTMENT, COUNT(WORKER_ID) as 'Number of Workers' 

FROM Worker 

GROUP BY DEPARTMENT 

HAVING COUNT(WORKER_ID) < 5;

14. Write an SQL query to show all departments along with the number of people in there.

SELECT DEPARTMENT, COUNT(DEPARTMENT) as 'Number of Workers' 

FROM Worker 

GROUP BY DEPARTMENT;

15. Write an SQL query to print the name of employees having the highest salary in each department.

SELECT t.DEPARTMENT,t.FIRST_NAME,t.Salary from(SELECT max(Salary) as TotalSalary,DEPARTMENT from Worker group by DEPARTMENT) as TempNew 

Inner Join Worker t on TempNew.DEPARTMENT=t.DEPARTMENT 

 and TempNew.TotalSalary=t.Salary;

16. Delete duplicate rows from a SQL Server Table?

DELETE FROM [Employee]

    WHERE ID NOT IN

    (

        SELECT MAX(ID) AS MaxRecordID

        FROM [Employee]

        GROUP BY [FirstName],[LastName],[Country]

    );

Using CTE:

WITH CTE([FirstName],[LastName],[Country],DuplicateCount)

AS (SELECT [FirstName],[LastName],[Country],

           ROW_NUMBER() OVER(PARTITION BY [FirstName],[LastName],[Country]

           ORDER BY ID) AS DuplicateCount

    FROM [Employee])

DELETE FROM CTE

WHERE DuplicateCount > 1;