Objective: Find out the reusable methods and create a super class for all the browsers like IE,FF,CH.

public abstract class WebDriver
{

public abstract void openBrowser(String url);

public abstract void closeBrowser();

}

Interface Definition:
-----------------------------

If the class contains 100% abstract methods then the class is defined as interface.
public interface WebDriver
{

public void open(String url);

public void close();

}
1. An interface contains 100% abstract methods.
2. In interface methods are by default public and abstract.

public interface WebDriver
{

void open(String url);

public abstract void close();

}
3. In interface, variables are 'public static final' by default.

public ->Accessible everywhere
static->Classname.variable
final->Constant. Once intialized we cannot re-assign the new value;

4. The final variables in interface are intialized at the time of declaration.
int i;//declaration
i=10;//intialization or Assignment

int i =10;//Declaration and intialization.

5.A class uses an interface should use an keyword called 'implements'.


IE,FF,CH

public class IEDriver implements WebDriver
{
void open(String url){}
public void close(){}
}

public class FFDriver implements WebDriver
{
void open(String url){}
public void close(){}
}

public class CHDriver implements WebDriver
{
void open(String url){}
public void close(){}
}

6. A class can implement multiple interfaces, but extends only one class at a time.

   A interface extends an another interfaces

7. A class together can use implements and extends keywords together.

public class ThreadEx extends ClassB implements Runnable,InterfaceA
{

}

If a class is implementing an interfaces then we can write as follows:

InterfaceName refV = new ClassName();

WebDriver      driver = new FFDriver();

driver.open("http://www.google.com");
driver.close();


final variables are constants
--------------------------------------
public final int i =20;
i=10;// not possible i is final

final classes cannot be extended
----------------------------------------
public final class String
{
}
public class A extends String// cannot extend an final class
{

}
final methods cannot be overriden
--------------------------------------------
public final void equals()
{


}
@Override:
-------------------
Whenever the same method name with same parameters available in the super class and 
subclass or interface and subclasses.. those methods are overriden methhods.
@Override is an annotation which is an special instruction to the compiler.

Advantages of re-usability:

1. Save time and effort
2. Maintenance of code is easy means if you want to modify the code. We will change the code in one place.








OOPs Concept Inheritance: 

1. The objective of inheritance is re-usability.

2. The process of acquiring the methods and variables from Super-class to Sub-Class is called Inheritance.

Class members are methods and variables.

Two types of class members -> static and nonstatic

Static Members are accessed using Class Name:
public static void display()
{

}

Non-Static Members are accessed using Object:
public void display()
{

}

Only object level class members are inherited to subclass.


3. Inheritance is achieved between two classes using the keyword called 'extends'. From now on-wards 'extends' means inheritance.

4. Single Inheritance is between two classes is achieved using the extends keyword

Class A
{
public int i=20;

public void display()
{
}

}

Class B extends ClassA
{

}



5. Multilevel Inheritance : mean the subclass(child) can access superclass(Father) and Superclass SuperClass (GrandFather) also.

  Class A   
  {


 }


 Class B extends Class A
 {


 }



 Class C extends Class B
 {


}

6. Multiple Inheritance:

   In java we cannot extend more than one class at a time.
   Multiple classes cannot be inherited at the same time.
   So, multiple inheritance is not supported in java.


   Class C extends Class B,Class A  //Not Valid in java

   Diamond Problem in java.


7. By Default a Class extends Object Class. So we can access the object class Members. Object is a class available in the package java.lang.

8. Only non-static variables and methods are inherited to the subclass.  Static variables and Methods are at the class level not at the object  level. So cannot be inherited to the subclass.

9. Global and Local Variables

public class Variables {


int a = 20; // Global variable

public static void main(String[] args) {

int a =10;
System.out.println(a); // local variable

Variables v = new Variables();
System.out.println(v.a);


}


}