class BankVaultDoor extends Door {    // The "extends" keyword used to tell java that BankVaultDoor inherits the functionality of Door.

​

    public void open () {

        enterCombination();

        pull;

    }

​

}

public class Door {

    public void open ()

    {

        push();     // Since this is just a generic "Door" we will assume the simplest opening method.

                    // The actual open method must be overridden by a subclass, as we see below.

                    // Later, a way to force a subclass to override a method will be demonstrated -- 

                    // but for this simple example will do for now.

    }

}