JAVA

abstract class in java

Sometimes we may come across a situation where we cannot provide 
implementation to all the methods in a class. We want to leave the 
implementation to a class that extends it. In such case we declare a class
as abstract.To make a class abstract we use key word abstract. 
Any class that contains one or more abstract methods is declared as abstract. 
If we don’t declare class as abstract which contains abstract methods we get 
compile time error.
  
  1)Abstract classes cannot be instantiated
  2)An abstarct classes contains abstract method, concrete methods or both.
  3)Any class which extends abstarct class must override all methods of abstract
    class
  4)An abstarct class can contain either 0 or more abstract method.    

abstract class in java

/*Abstract class:
A class which is declared as abstract is known as an abstract class. 
It can have abstract and non-abstract methods. It needs to be extended 
and its method implemented. It cannot be instantiated.

*/

// Example of abstract class
abstract class A{}  
// Example of Abstract class that has an abstract method
abstract class Bike{  
  abstract void run();  
}  
class Honda4 extends Bike{  
void run(){System.out.println("running safely");}  
public static void main(String args[]){  
 Bike obj = new Honda4();  
 obj.run();  
}  
}  

abstract class java constructor

/**
 * Simple Java program to prove that abstract class can have constructor in Java.
 * @author http://java67.blogspot.com
 */
public class AbstractConstructorTest {

    public static void main(String args[]) {
       Server server = new Tomcat("Apache Tomcat");
       server.start();
    }
}

abstract class Server{
    protected final String name;
   
    public Server(String name){
        this.name = name;
    }
   
    public abstract boolean start();
}

class Tomcat extends Server{
   
    public Tomcat(String name){
        super(name);
    }

    @Override
    public boolean start() {
       System.out.println( this.name + " started successfully");
       return true;
    }
   
}

Output:
Apache Tomcat started successfully

abstract class in java

Sometimes we may come across a situation
where we cannot provide implementation to
all the methods in a class. We want to leave the 
implementation to a class that extends it.
  In that case we declare a class
as abstract by using abstract keyword on method
signature.In my framework I have created my
PageBase class as super
class of the all page classes. 
I have collected all common elements
and functions into PageBase class and
all other page classes extent PageBase class.
By doing so, I don't have to locate very
common WebElements and it provides
reusability in my framework.
Also
1)Abstract classes cannot be instantiated
2)An abstarct classes contains abstract method,
concrete methods or both.
3)Any class which extends abstarct class must
  override all methods of abstract class
4)An abstarct class can contain either
  0 or more abstract method.   

how to use an abstract class in java

interface methods{
    public void hey();
    public void bye();
}

//unable to implement all the abstract methods in the interface so 
// the other class automatically becomes abstract
abstract class other implements methods{
    public void hey(){
        System.out.println("Hey");
    }
}

//able to implement all the methods so is not abstract
class scratch implements methods {
    public void hey(){
        System.out.println("Hey");
    }
    public void bye() {
        System.out.println("Hey");
    }
}

Can you add a constructor to an abstract class

We can create constructor in abstract class , it does’nt give any compilation 
error. 

Java Abstract Class and Method

abstract class Language {

  // method of abstract class
  public void display() {
    System.out.println("This is Java Programming");
  }
}

class Main extends Language {
  public static void main(String[] args) {
    
    // create an object of Main
    Main obj = new Main();

    // access method of abstract class
    // using object of Main class
    obj.display();
  }
}

abstract class java

Abstract classes have some special features:

it's impossible to create an instance of an abstract class;
an abstract class can contain abstract methods that must be implemented in non-abstract subclasses;
it can contain fields and non-abstract methods (including static);
an abstract class can extend another class, including abstract;
it can contain a constructor.

how to create an abstract class in java

abstract class scratch{
  
}

can abstract class have constructor

In Java, Abstract classes can have constructors even when they are only called from their concrete subclasses.

what are abstract classes in java

Sometimes we may come across a situation
where we cannot provide implementation to
all the methods in a class. We want to leave the 
implementation to a class that extends it.
  In that case we declare a class
as abstract by using abstract keyword on method
signature.In my framework I have created my
PageBase class as super
class of the all page classes. 
I have collected all common elements
and functions into PageBase class and
all other page classes extent PageBase class.
By doing so, I don't have to locate very
common WebElements and it provides
reusability in my framework.

i)List<String> webs=driver.getWindowHandles();
=>create a list first to store web URLs in list

ii)findElements evaluates multiple elements so therefore will assigned to List <WebElement>

iii)To handle dynamic elements store it in the list and identify by index:
List<WebElement> all=driver.findElements(By.tagname(“”)); (or other locators).
Also
1)Abstract classes cannot be instantiated
2)An abstarct classes contains abstract method,
concrete methods or both.
3)Any class which extends abstarct class must
  override all methods of abstract class
4)An abstarct class can contain either
  0 or more abstract method.  

Java Abstract Class

// create an abstract class
abstract class Language {
  // fields and methods
}
...

// try to create an object Language
// throws an error
Language obj = new Language();