Solid Design Principle # Open - Closed

Open = Open for extend existing behavior
Closed = Closed for change existing code

package solid.openclosed;

public abstract class Animal {

    protected String name; //closed to modification

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    abstract public void move(); //open for extension

    public void callMe() {
        System.out.println("My name is " + getName());
    }
}
package solid.openclosed;

public class Dog extends Animal {

    @Override
    public void move() {
        System.out.println("I can Run.");
    }

}
import solid.openclosed.Animal;
import solid.openclosed.Dog;

public class Main {

    public static void main(String[] args) {

        Animal dog = new Dog();
        dog.setName("MooMoo");
        dog.move();
        dog.callMe();
    }
}

Run แล้วจะได้

I can Run.
My name is MooMoo