Abstract Classes

An abstract class has the following key characteristics:

• It defines the behavior for each of the subclasses, but we cannot directly instantiate the abstract class itself.
• It allows us to create abstract methods.
  • An abstract method is a method that does not contain an implementation body. Instead, it simply provides a header for the method.
  • Subclasses that extend an abstract class are required to override all abstract methods and provide a specific implementation.

Example: Abstract Vehicle Class

Here's the example we looked at in the video. To ensure that we will not be able to directly instantiate Vehicle objects from this class, we define it using the abstract keyword:

public abstract class Vehicle {
    protected String start;
    protected String stop;
    protected String direction;

    public Vehicle(String start, String stop,
                                  String direction) {
        this.start = start;
        this.stop = stop;
        this.direction = direction;
    }

    public abstract void speed();   

}

Next, we use the Extends keyword to have our Car class extend the Vehicle class:

public class Car extends Vehicle {

    public Car() {
    super("Car start", "Car stop", "Car direction");
    }
    @Override
    public void speed() {
        System.out.println("55");
    }
}

Thus, although we cannot directly instantiate objects from the abstract Vehicle class, we can instantiate objects from the Car class, and they will have all the behavior of a Vehicle.