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Abstract

Abstract classes are identified by the keyword abstract. They cannot be instantiated but require a subclass that is inherited from the abstract class. Abstract classes are used to implement a concept that the subclass will then complete. Abstract methods can also be declared in abstract classes. Abstract methods do not allow code or declarations in the method. A subclass must extend the abstract class to use the abstract method.

Example

The following is an example of an abstract class. The Car class extends the abstract class Vehicle. This allows the Car class to override the printInfo() method and it allows you to add functionality to the operate() method that was not included in the abstract class.

Parent Class Vehicle Which is abstract

abstract class VehicleClass{ 
    str owner = "Rumman";       
     int age = 25;         

    // below method is not abstract         
    void printInfo()        {  
        Info(strfmt("%1, %2",owner, age));       
    }    

    // This is a abstract method
     abstract void operate() {}

}

Child Class Car which is extending the Parent Class

class CarClass extends VehicleClass{   
    str model = "Model Awesome";     
 
    // this printInfo method is overrding the parent method    
    void printInfo()    {        
        // overriding default functionality  
        Info(strfmt("%1, %2, %3",owner, age, model)); 
    }      

    // Here is the implementation of operate method which is present in the abstract class    
    void operate()    {  
        Info('running');    
    }   

    public static void main(Args arg)    { 
        CarClass obj = new CarClass(); 
        obj.printInfo();    // call non abstract method   
        obj.operate();    // class abstract method
    }
  }

Output

running
Rumman, 25, Model Awesome

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