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/**
 * Java abstract class example
 * Abstract class represents skeleton of the classes
 * which will extend this abstract class
 */

    /**
     * Vehicle abstract class is a general class of all vehicles
     * It contains methods and attributes common to all vehicles
     * but you can't create an instance of the Vehicle class
     * Vehicle class is used as a basic structure for all specific vehicles (car,bus...)    
     */
    abstract class Vehicle {
        //subclasses will inherit an attribute
        int maxSpeed;
        //subclasses must implement this method 
        //(otherwise they have to be declared as abstract classes)
        abstract void showMaxSpeed(); 
        //subclass will have this method (through inheritance) as is (default implementation)
        //or they may implement their own implementation (override a method)
        int getWheelsNumber() {
           return 4;
        }
  }
   
   /**Car IS-A Vehicle*/
   class Car extends Vehicle {
     public Car() {
         maxSpeed = 180; 
     }
     
     public void showMaxSpeed() {
        System.out.println("Car max speed: " + maxSpeed + " km/h");
     }
     //Car class will inherit getWheelsNumber() method from the parent class
     //there is no need to override this method because default implementation
     //is appropriate for Car class - 4 wheels
   }
   
   /**Bus IS-A Vehicle*/
   class Bus extends Vehicle {
     public Bus() {
         maxSpeed = 100; 
     }
     
     public void showMaxSpeed() {
        System.out.println("Bus max speed: " + maxSpeed + " km/h");
     }
     //Bus class will override this method because the default implementation
     //is not appropriate for Bus class
     public int getWheelsNumber() {
         return 6;
     }
   }
   
   /**Truck IS-A Vehicle*/
   class Truck extends Vehicle {
     public Truck() {
         maxSpeed = 80;
     }
     
     public void showMaxSpeed() {
        System.out.println("Truck max speed: " + maxSpeed + " km/h");
     }
     //Truck class will override this method because the default implementation
     //is not appropriate for Bus class
     public int getWheelsNumber() {
         return 10;
     }
   }

public class AbstractClassExample {
   
   public static void main(String[] args) {
     Vehicle car = new Car();
     Vehicle bus = new Bus();
     Vehicle truck = new Truck();
     car.showMaxSpeed();
     bus.showMaxSpeed();
     truck.showMaxSpeed();
     System.out.println("Wheels number-car:" + car.getWheelsNumber() + 
             ", bus:" + bus.getWheelsNumber() + ", truck:" + truck.getWheelsNumber());
   }
}