#Learning and Practice OOPS from scratch with .NET Day 2:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
Console.WriteLine("Hello");
Console.WriteLine("Plz enter your name");
String Username = Console.ReadLine();
Console.WriteLine("Plz enter your last name");
String LastName = Console.ReadLine();
Console.WriteLine("Welcome " + Username);
Console.WriteLine("Welcome {0} {1}", Username,LastName);
}
}
}
Day 5:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
int number = 15;
int num = 10;
bool isNum = num == 10 ? true : false;
bool isNumber = true;
if (number == 10)
{
isNumber = true;
}
else
{
isNumber = false;
}
Console.WriteLine("number==10 is {0}", isNumber);
Console.WriteLine("number==10 is {0}", isNum);
}
}
}
Day 6:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
int? TcketsOnSale = null;
bool? AreYouMajor = null;
int AvailableTckets;
if(TcketsOnSale==null)
{
AvailableTckets = 0;
}
else
{
AvailableTckets = TcketsOnSale.Value;
}
Console.WriteLine("Available Tickets {0}", AvailableTckets);
int AvTickets = TcketsOnSale ?? 0;// returns the value of its left-hand operand if it isn't null; otherwise, it evaluates the right-hand operand
Console.WriteLine("Available Tickets {0}", AvTickets);
}
}
}
Day 7:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
int a = 100;
float b = a;
Console.WriteLine(b);
float c = 123.34F;
int d = (int)c;
int e = Convert.ToInt32(c);
Console.WriteLine(d);
Console.WriteLine(e);
float f= 12311111111111111111.34F;
int g = (int)f;
int h = Convert.ToInt32(g);
Console.WriteLine(g);
Console.WriteLine(h);
string s = "100";
int i = int.Parse(s);
Console.WriteLine(i);
string st = "100ST";
int j = 0;
bool isConversionSuccessfull = int.TryParse(st, out j);
if (isConversionSuccessfull)
{
Console.WriteLine(j);
}
else
{
Console.WriteLine("Please enter valid no");
}
}
}
}
Day 8:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
int[] evenNo = new int[3];
evenNo[0] = 0;
evenNo[1] = 1;
evenNo[2] = 3;
evenNo[3] = 5;
Console.WriteLine(evenNo[2]);
}
}
}
Day 11:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
Console.WriteLine("Enter a no");
int n = Convert.ToInt32(Console.ReadLine());
switch (n)
{
case 10:
case 20:
case 30:
Console.WriteLine("Your no is { }",n);
break;
default:
Console.WriteLine("Wrong No");
break;
};
}
}
}
Day 12:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
int TotalCost=0;
Begin:
Console.WriteLine("Small Coffee 1 - Medium Coffee 2 - Large Coffee 3");
int n = int.Parse(Console.ReadLine());
switch (n)
{
case 1:
TotalCost += 1;
break;
case 2:
TotalCost += 2;
break;
case 3:
TotalCost += 3;
break;
default:
Console.WriteLine("No Coffee for your choice {0}- Please try again...",n);
goto Begin;
}
Console.WriteLine("Bill amount is {0}", TotalCost);
Middle:
Console.WriteLine("Do you want anoter coffee? Yes or No");
string s = Console.ReadLine();
switch (s.ToUpper())
{
case "YES":
goto Begin;
case "NO":
break;
default:
Console.WriteLine("Wrong choice {0}- Please try again...", s);
goto Middle;
}
Console.WriteLine("Thank you for shopping with me! Bill amount is {0}", TotalCost);
}
}
}
Day14:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
string userChoice = string.Empty;
do
{
Console.WriteLine("Please enter your target");
int n = int.Parse(Console.ReadLine());
int start = 0;
while (start <= n)
{
Console.Write(start + " ");
start = start + 2;
}
do
{
Console.WriteLine("Do you want to continue - Yes or No");
userChoice = Console.ReadLine().ToUpper();
if (userChoice != "YES" && userChoice != "NO")
{
Console.WriteLine("Please enter a valid choice Yes or No");
}
} while (userChoice != "YES" && userChoice != "NO");
} while (userChoice == "YES");
}
}
}
Day14 2:
using System;
using System.Collections.Generic;
using System.Text;
namespace IntroductionToCSharp
{
class Program
{
static void Main()
{
int TotalCost = 0;
int userChoice;
string userAgainChoice = string.Empty;
do
{
do
{
Console.WriteLine("Small Coffee 1 - Medium Coffee 2 - Large Coffee 3");
while (!int.TryParse(Console.ReadLine().Trim(), out userChoice))
{
if (userChoice==0)
{
Console.WriteLine("Please provide a number from above");
}
}
switch (userChoice)
{
case 1:
TotalCost += 1;
break;
case 2:
TotalCost += 2;
break;
case 3:
TotalCost += 3;
break;
default:
Console.WriteLine("No Coffee for your choice {0}- Please try again...", userChoice);
break;
}
} while (userChoice != 1 && userChoice != 2 && userChoice != 3);
Console.WriteLine("Bill amount is {0}", TotalCost);
do
{
Console.WriteLine("Do you want anoter coffee? Yes or No");
userAgainChoice = Console.ReadLine().ToUpper();
if (userAgainChoice != "YES" && userAgainChoice != "NO")
{
Console.WriteLine("Wrong choice {0}- Please try again...", userAgainChoice);
}
} while (userAgainChoice != "YES" && userAgainChoice != "NO");
} while (userAgainChoice != "NO");
Console.WriteLine("Thank you for shopping with me! Bill amount is {0}", TotalCost);
}
}
}
Day 15:
using System;
class Program
{
static void Main()
{
int[] arr = new int[4];
arr[0] = 100;
arr[1] = 101;
arr[2] = 102;
int i = 0;
while (i < arr.Length)
{
Console.WriteLine(arr[i]);
i++;
}
for (int j = 0; j < arr.Length; j++)
{
Console.WriteLine(arr[j]);
}
foreach(int k in arr)
{
Console.WriteLine(k);
}
for(int l = 0; l <= 20; l++)
{
if(l % 2 == 1)
continue;
Console.WriteLine(l);
}
}
}
day 16:
using System;
class Program
{
static void Main()
{
int[] a = new int[3];
a[0] = 100;
a[1] = 101;
a[2] = 102;
Program program = new Program();
program.printArray(a);
Program.printArray2(a);
}
public void printArray(int[] arr)
{
foreach (int k in arr)
{
Console.WriteLine(k);
}
}
public static void printArray2(int[] arr)
{
foreach (int k in arr)
{
Console.WriteLine(k);
}
}
}
Day 17
using System;
class Program
{
public static void Main()
{
int i = 0;
Program.simpleMethod(i);
Console.Write(i);
}
public static void simpleMethod(int j)
{
j = 101;
}
}
using System;
//----------------------------------
class Program
{
public static void Main()
{
int i = 0;
Program.simpleMethod(ref i);
Console.Write(i);
}
public static void simpleMethod(ref int j)
{
j = 101;
}
}
//-------------------------------
using System;
class Program
{
public static void Main()
{
int[] Numbers = new int[3];
Numbers[0] = 100;
Numbers[1] = 101;
Numbers[2] = 102;
Program.paramsMethod();
Program.paramsMethod(Numbers);
Program.paramsMethod(1,2,3,6,7,70,12);
}
public static void paramsMethod(params int[] num)
{
Console.WriteLine("There are {0} numbers in the array", num.Length);
foreach(int i in num)
{
Console.WriteLine(i);
}
}
}
Day18
using System;
using PATA=ProjectA.TeamA;
using PATB=ProjectA.TeamB;
class Program
{
public static void Main()
{
//ProjectA.TeamA.ClassA.Print();
//ProjectA.TeamB.ClassA.Print();
PATA.ClassA.Print();
PATB.ClassA.Print();
}
}
namespace ProjectA
{
namespace TeamA
{
class ClassA
{
public static void Print()
{
Console.WriteLine("My Team is TeamA");
}
}
}
}
namespace ProjectA
{
namespace TeamB
{
class ClassA
{
public static void Print()
{
Console.WriteLine("My Team is TeamB");
}
}
}
}
Day 19:
Constructor does not have return type and same name as class, can take parameters
Destructor used to call automatically to clean resources by garabage collector in C#, no return type and no parameters
Default constructor does not have any parameters
Paramiterized Constructor: Used to create instance of a class by passing the required parameter of the class
using System;
class Customer
{
string _firstName;
string _lastName;
public Customer() :
this("No FirstName","No LastName")
{
}
public Customer(string FirstName, string LastName)
{
this._firstName = FirstName;
this._lastName = LastName;
}
public void printFullName()
{
Console.WriteLine("Full name is {0}", this._firstName + " " + this._lastName);
}
~Customer()
{
}
public static void Main()
{
Customer custormer1 = new Customer("Chinmoy","Jana");
Customer custormer2 = new Customer();
custormer1.printFullName();
custormer2.printFullName();
}
}
public class LandingPage {
WebDriver driver;
WebDriverWait wait;
public LandingPage(WebDriver driver, WebDriverWait wait) {
this.driver=driver;
this.wait = wait;
}
} public class HomePageTest extends Base{ LandingPage l; public WebDriver driver; public WebDriverWait wait; public void LogInTry(){ l = new LandingPage(driver,wait);//passing same object instances while creating the object of the parent class } }
Day20:
by default access modifier is private
static constructor called only once no matter how many times being called and it is called before instance constructor
using System;
public class Circle
{
public static float _PI;
int _Radius;
static Circle()
{
Console.WriteLine("Static Constructor Called");
Circle._PI = 3.141F;
}
public Circle(int Radus)
{
Console.WriteLine("Instance Constructor Called");
this._Radius = Radus;
}
public float CalculateArea()
{
return Circle._PI * this._Radius * this._Radius;
}
}
public class Program
{
public static void Main()
{
Circle circle1 = new Circle(5);
float Area1 = circle1.CalculateArea();
Console.WriteLine("{0}",Area1);
Circle circle2 = new Circle(10);
float Area2 = circle2.CalculateArea();
Console.WriteLine("{0}", Area2);
Console.WriteLine(Circle._PI);
}
}
Day 21:
One class cannot inheritate from multiple base class but multiple class can be inheritate from one base class
using System;
public class Employee
{
public string FirstName;
public string LastName;
public string Email;
public void PrintEmployeeDetails()
{
Console.WriteLine(FirstName +" "+ LastName);
Console.WriteLine(Email);
Console.WriteLine("No such Property");
}
}
public class FullTimeEmployee : Employee
{
public float YearlySalary;
}
public class PartTimeEmployee : Employee
{
public float HourlySalary;
}
public class A : FullTimeEmployee
{
public string Designation;
}
public class Program
{
public static void Main()
{
FullTimeEmployee fullTimeEmployee = new FullTimeEmployee();
fullTimeEmployee.FirstName = "Priya";
fullTimeEmployee.LastName = "Paul";
fullTimeEmployee.Email = ppaul@gmail.com;
fullTimeEmployee.YearlySalary = 85000.00F;
fullTimeEmployee.PrintEmployeeDetails();
PartTimeEmployee partTimeEmployee = new PartTimeEmployee();
partTimeEmployee.FirstName = "Pagli";
partTimeEmployee.LastName = "Paul";
partTimeEmployee.Email = pgpaul@hotmail.com;
partTimeEmployee.HourlySalary = 50.00F;
partTimeEmployee.PrintEmployeeDetails();
}
}
//---------------------------------------------------
//Parent class contructor called first
//Using base keyword in child class contructor, child class can choose base class contructor
using System;
public class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Class Contructor Called");
}
public ParentClass(string Message)
{
Console.WriteLine("Parent Class Contructor 2 Called");
}
}
public class ChildClass : ParentClass
{
public ChildClass() : base("Controlling Parent Class Constructor")
{
Console.WriteLine("Child Class Constructor called");
}
}
public class Program
{
public static void Main()
{
ChildClass childClass = new ChildClass();
}
}
//Day 22:
//Instance of clild class object prefers child class method over parent class method, that means inherited method hides. //New keyword used to make it intentional hide //base keyword used in child class properties to use base class properties
using System; public class Employee { public string FirstName; public string LastName; public void printName() { Console.WriteLine(FirstName + " " + LastName + "- Parent Class"); } }
public class PartTimeEployee : Employee { public new void printName() { base.printName(); // Call the parent class method Console.WriteLine(FirstName + " " + LastName + "- Child Class"); } }
public class FullTimeEmployee : Employee { public int Salary; public new void printName() { Console.WriteLine(FirstName + " " + LastName + "- Child Class"); } }
public class Program { public static void Main() { PartTimeEployee PTE = new PartTimeEployee(); PTE.FirstName = "Chinmoy"; PTE.LastName = "Jana"; PTE.printName(); FullTimeEmployee FTE = new FullTimeEmployee(); FTE.FirstName = "Sanu"; FTE.LastName = "Jana"; FTE.printName(); ((Employee)FTE).printName(); // Call the parent class method //FullTimeEmployee FTE1 = new Employee(); Not possible Employee FTE2 = new FullTimeEmployee(); // Base class reference variable can point to child class object FTE.FirstName = "Priya"; FTE.LastName = "Jana"; FTE.Salary = 1000; //FTE2.Salary = 1000; Cannot access child object FTE2.printName(); // Call the parent class method } }
Day23
//Polymorphism: Invoke derived class method using parent class reference variable at runtime //Run-Time Polymorphism: using System; public class Employee { public string FN = "FN"; public string LN = "LN"; public virtual void printName() { Console.WriteLine(FN + " " + LN); } }
public class PartTimeEmployee : Employee { public override void printName() { Console.WriteLine(FN + " " + LN + "PartTimeEmployee"); } }
public class FullTimeEmployee : Employee { public override void printName() { Console.WriteLine(FN + " " + LN + "FullTimeEmployee"); } }
public class TemporaryTimeEmployee : Employee { public new void printName()//New keyword used to make it intentional hide { Console.WriteLine(FN + " " + LN + "TemporaryTimeEmployee"); } }
public class Program { public static void Main() { Employee[] employees = new Employee[4]; employees[0] = new PartTimeEmployee(); employees[1] = new FullTimeEmployee(); employees[2] = new TemporaryTimeEmployee();// Will not call clild class as it's intance of parent class employees[3] = new Employee(); foreach( Employee e in employees) { e.printName(); } Employee[] employees2 = new TemporaryTimeEmployee[1]; employees2[0] = new TemporaryTimeEmployee();// Will not call clild class foreach (Employee e in employees2) { e.printName(); }
}
}
Day 24: Method Hiding vs Method Overriding
using System; public class BaseClass { public virtual void print() { Console.WriteLine("I am the Base Class"); } }
public class DerivedClassOverride : BaseClass { public override void print() { Console.WriteLine("I am the Child Class - override"); } }
public class DerivedClassHiding : BaseClass { public new void print() { Console.WriteLine("I am the Child Class - hiding"); } }
public class Program { public static void Main() { BaseClass baseClassForOverride = new DerivedClassOverride(); baseClassForOverride.print(); BaseClass baseClassForHiding = new DerivedClassHiding(); baseClassForHiding.print(); } }
//Day25
//Overloading: Based on Params(no, datatype), name of method ////Compile-Time Polymorphism: //Compile error if try to overload by only changing retun type or params modifier
using System;
public class Program {
public static void Main()
{
add(1,2);
}
public static void add(int a, int b)
{
Console.WriteLine("Addition is {0}", a+b);
}
public static void add(int a, int b, int c)
{
Console.WriteLine("Addition is {0}", a + b);
}
public static void add(int a, float b)
{
Console.WriteLine("Addition is {0}", a + b);
}
public static void add(int a, int b, out int sum)
{
sum = a + b;
Console.WriteLine("Addition is {0}", sum);
}
public static int add(int a, int b)
{
Console.WriteLine("Addition is {0}", a + b);
return a + b;
}
public static void add(int a, int b, params int[] list)
{
list[0] = a;
list[1] = b;
Console.WriteLine("Addition is {0}", a + b);
}
public static void add(int a, int b, int[] list)
{
list[0] = a;
list[1] = b;
Console.WriteLine("Addition is {0}", a + b);
}
}
//Day 25: Why Properties?
//To maintain business rules for the class objects
//Example: ID Should not be -ve, Name should be not null and Passmark cannot be changed
using System;
public class Student
{
public string Name;
public int ID;
public int Passmark = 35;
}
public class Program {
public static void Main()
{
Student C1 = new Student();
C1.ID = -12;
C1.Name = null;
C1.Passmark = 40;
Console.WriteLine("ID is {0}, Name is {1}, PassMark is {2}", C1.ID, C1.Name, C1.Passmark);
}
}
// To achieve the business rules, we make properties Private first - this is encapsulation
using System;
public class Student
{
private string _name;
private int _iD;
private int _passmark = 35;
public int GetPassMark()
{
return this._passmark;
}
public void SetID(int ID)
{
if (ID < 0)
{
throw new Exception("ID cannot be negative");
}
else
this._iD = ID;
}
public int GetID()
{
return this._iD;
}
public void SetName(string Name)
{
if (string.IsNullOrEmpty(Name))
{
throw new Exception("Name cannot be Null or Empy");
}
else
this._name = Name;
}
public string GetName()
{
return string.IsNullOrEmpty(this._name) ? "No Name" : this._name;
}
}
public class Program {
public static void Main()
{
Student C1 = new Student();
//C1.SetID(-11);
C1.SetID(101);
//C1.SetName("");
Console.WriteLine("ID is {0}, Name is {1}, Passmark is {2}", C1.GetID(), C1.GetName(), C1.GetPassMark());
}
}
//Get Set Accessors for doing encapsulation
// If no additional logic is there, we can use auto implemented get set method
using System;
public class Student
{
private string _name;
private int _iD;
private int _passmark = 35;
public int Passmark
{
get
{
return this._passmark;
}
}
public int ID
{
set
{
if (value < 0)
{
throw new Exception("ID cannot be negative");
}
this._iD = value;
}
get
{
return this._iD;
}
}
public string Name
{
set
{
if (string.IsNullOrEmpty(value))
{
throw new Exception("Name cannot be Null or Emty");
}
this._name = value;
}
get
{
return string.IsNullOrEmpty(this._name) ? "No Value Provided" : this._name;
}
}
}
public class Program {
public static void Main()
{
Student C1 = new Student();
//C1.SetID(-11);
C1.ID = 101;
//C1.Name ="";
C1.Name = "Priya";
Console.WriteLine("ID is {0}, Name is {1}, Passmark is {2}", C1.ID, C1.Name, C1.Passmark);
}
}
Day 28:
Structs
using System;
public struct Customer
{
private int _id;
private string _name;
public int ID
{
set { this._id = value; }
get { return this._id; }
}
public string Name { get => _name; set => _name = value; }
public Customer(int ID, string Name)
{
this._id = ID;
this._name = Name;
}
public void PrintCustomer()
{
Console.WriteLine("ID is {0} and Name is {1}",this._id,this._name);
}
}
public class Program
{
public static void Main()
{
Customer C1 = new Customer(100,"Priya");
C1.PrintCustomer();
Customer C2 = new Customer();
C2.ID = 101;
C2.Name = "Pagli";
C2.PrintCustomer();
Customer C3 = new Customer
{
ID = 102,
Name = "Peter"
};
C3.PrintCustomer();
}
}
Day 29: //Structs Vs Class
Object reference variable store in Stack but object stores in Heap. Value type variable stores in Stack
Class are store in stack but structs are in Heap.
The object of a reference variable destroyed by garbage collector not after the scope
Assigning one object variable to another, does not copy the object in memory rather pointing to the same loaction in Heap.
Changing the value of the variable of one object will change for another as it points to same location.
using System;
public class Customer
{
public int ID { get; set; }
public string Name { get; set; }
}
public class Program
{
public static void Main()
{
int i = 100;
int j = i;
j = j + 2;
Console.WriteLine("i={0} and j={1}", i, j);
Customer C1 = new Customer();
C1.ID = i;
C1.Name = "Priya";
Customer C2 = C1;
C2.Name = "Pgli";
Console.WriteLine("C1.Name = {0} and C2.Name = {1}", C1.Name, C2.Name);
}
}
// Class can have destructor but Structor can't have
using System;
public class Customer
{
public int ID { get; set; }
public string Name { get; set; }
~Customer()
{
}
}
public class Program
{
public static void Main()
{
}
}
using System;
public struct Customer
{
public int ID { get; set; }
public string Name { get; set; }
~Customer()//Error
{
}
}
public class Program
{
public static void Main()
{
}
}
// Class can have explicit parameters less contructor but struct can't
using System;
public struct Customer
{
public int ID { get; set; }
public string Name { get; set; }
public Customer()//Error
{
}
}
public class Program
{
public static void Main()
{
}
}
// Struct can't inheritate from another class but both can inheritate from same Interface
//Class or struct cannot inheritate from anoter struct, like sealed class.
using System;
public sealed class Customer // Cannot inheritate
{
public int ID { get; set; }
public string Name { get; set; }
public Customer()
{
}
}
public class Program : Customer// Error
{
public static void Main()
{
}
}
Day 30: Interface
//Contains Properties, Method, Delegates but no implementation unlike Class
// Interface members are public by default
//Interface cannot have fields
//Class needs to do the implementation if Inherites a Interface
//Class can inheritate from multiple Interfaces
//Class cannot inheritate from multiple classes
// if a class inherits from a Interface and the interface again inherits from anoter Interface then this class have to implement all the properties of all the interfaces
//Cannot create instances of Interface but an interface reference variable can point to an derived class object
using System;
interface ICustomer1
{
void Print1();
}
interface ICustomer2 : ICustomer1
{
void Print2();
}
public class Customer : ICustomer2
{
public void Print1()
{
Console.WriteLine("Print1");
}
public void Print2()
{
Console.WriteLine("Print2");
}
}
public class Program
{
public static void Main()
{
//ICustomer1 customer1 = new ICustomer1();//Cannot create instances of Interface
ICustomer1 customer = new Customer();
customer.Print1();
//customer.Print2();//Parent Interface does not contain the definition of the function
ICustomer2 customer2 = new Customer();
customer2.Print1();
customer2.Print2();
}
}
Day 31:
//Explicit interface implementation can be done only via interface reference variable not class reference variable
// Access modifier are not allowed for explicit interface implemented interface members
// To make a default interface method, impplement that method normally and explicit others
using System;
interface I1
{
void InterfaceMethod();
}
interface I2
{
void InterfaceMethod();
}
interface I3
{
void InterfaceMethod();
}
public class Program : I1, I2, I3
{
void I2.InterfaceMethod()
{
Console.WriteLine("Interface 2 Method");
}
void I1.InterfaceMethod()
{
Console.WriteLine("Interface 1 Method");
}
public void InterfaceMethod()
{
Console.WriteLine("Interface 3 Method");
}
public static void Main()
{
Program p1 = new Program();
((I2)p1).InterfaceMethod();
((I1)p1).InterfaceMethod();
I2 i2 = new Program();
i2.InterfaceMethod();
p1.InterfaceMethod();
}
}
Day 32:
// Abstract members cannot have implementation in the abstract class
//Abstract class have abstract members also can have non abstract members
//Cannot instantiate abstract class
//If a class inherited from a abstract class either needs to implement the properties or mark himself as abstract
//Abstract class can only used as a Base class but sealed class cannot be used as base class
using System;
public abstract class Customer
{
public abstract void Print1();
public void Print2()
{
Console.WriteLine("Print2");
}
}
public class Program : Customer
{
public override void Print1()
{
Console.Write("Print 1");
}
public static void Main() {
Program p = new Program();
p.Print1();
p.Print2();
Customer c = new Program();
c.Print1();
c.Print2();
}
}
Day 33:
//Abstract Class VS Interface
//Abstract class can have implementation of some of his members but Interface cannot have any implementation
//Abstract class members can have access modifier but Interface members are always public
//Abstract can have fields but interface cannot have fields
//Abstract class can inherited from another abstract class/interface/non abstract class but interface can only inheritate from anoter interface
//Class can inheritate from multiple interfaces but class cannot inheritate from multiple classes
Array vs ArrayList: for dynamic size int[] arr = new int[5]; arr[0]=1; arr[1]=2;
int[] arr = {1,2};
ArrayList<String> arr = new ArrayList<String>();
arr.add("abc");
arr.add("test");
arr.add("peter");
MultiDimensional Array: Collection of arrays