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();  
}  
}  

how to make abstract method in java

public abstract class Account {		//abstract class //perent class
    protected int accountNumber;
    protected Customer customerObj;
    protected double balance;
  	//constructor
  	public Account(int saccountNumber, Customer scustomerObj,double sbalance){
        accountNumber = saccountNumber;
        customerObj = scustomerObj;
        balance = sbalance;
    }
  	// abstract Function
    public abstract boolean withdraw(double amount); 
}   

public class SavingsAccount extends Account { // child class
    private double minimumBalance;
  	// constructor
    public SavingsAccount(int saccountNumber, Customer scustomerObj, double sbalance, double sminimumBalance) {
        super(saccountNumber, scustomerObj, sbalance);
        minimumBalance = sminimumBalance;
    }
	// Implementation of abstract function in child class
    public boolean withdraw(double amount) {
        if (balance() > minimumBalance && balance() - amount > minimumBalance) {
            super.setBalance(balance() - amount);
            return true;
        } else {
            return false;
        }
    }
}

What are abstract methods in java

An abstract method is the method which does’nt have any body. 
Abstract method is declared with
keyword abstract and semicolon in place of method body.

  public abstract void <method name>();
Ex : public abstract void getDetails();
It is the responsibility of subclass to provide implementation to 
abstract method defined in abstract class

how to create object of abstract class in java

We cannot create objects of an abstract class. To implement features of an abstract class, we inherit subclasses from it and create objects of the subclass. A subclass must override all abstract methods of an abstract class. However, if the subclass is declared abstract, it's not mandatory to override abstract methods.

is it necessary for abstract class to have abstract method

No, abstract class can have zero abstract methods.

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");
    }
}

is it necessary for abstract class to have abstract method

Abstract classes CAN have non-abstract methods. 

can abstract class have non abstract methods in java

abstract class AbstractDemo { // Abstract class
   private int i = 0;
   public void display() { // non-abstract method
      System.out.print("Welcome to Tutorials Point");
   }
}
public class InheritedClassDemo extends AbstractDemo {
   public static void main(String args[]) {
      AbstractDemo demo = new InheritedClassDemo();
      demo.display();
   }
}

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

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.  

what is abstract class with example

<?php
abstract class Cars
{
    abstract function car_details();
}
class Maruti extends Cars
{
    function car_details()
    {
        echo "Maruti Details";
    }
}
class Honda extends Cars
{
    function car_details()
    {
        echo "<br>Honda Details<br>";
    }
}

class Scoda extends Cars
{
    function car_details()
    {
        echo "<br>Scoda Details<br>";
    }
}

$obj = new Maruti();
$obj -> car_details();

$obj1 = new Honda();
$obj1 -> car_details();

$obj2 = new Scoda();
$obj2 -> car_details();
?>

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();

Java Abstract Method

abstract void display();