X++ interfaces

An interface specifies a set of public instance methods. An interface defines and enforces similarities between unrelated classes without having to derive one class from the other.

All interfaces are public, even if you don't explicitly add the public keyword in front of the interface keyword in interface declaration. The methods on an interface are also public. Explicit inclusion of the keyword public is optional.

To create an interface, follow these steps.

1. In Server Explorer, right-click the project, and then click Add.
2. In the New Item dialog box, select Interface, and then enter a name for the interface.
3. Click Add.

When you add the implements keyword on a class declaration, the class must declare and define the methods that are specified by the interface. A class declaration can implement multiple interfaces. List the interfaces after the single occurrence of the implements keyword, and separate the interface names by using commas.

All interface methods that a class implements must be explicitly declared as public. A class that implements an interface must also be declared as public. An interface can extend another interface by using the extends keyword, however, an interface can't extend more than one interface.

It is customary to preface the name of an interface with I.

Interface example

In the following code example, the Automobile class implements the IDrivable interface. The is keyword tests whether a class implements an interface.

interface IDrivable
{
    int getSpeed()
    {
    }

    void setSpeed(int newSpeed)
    {
    }
}

class Automobile implements IDrivable
{
    int speed;

    public int getSpeed()
    {
        return speed;
    }

    public void setSpeed(int newSpeed)
    {
        speed = newSpeed;
    }
}

class UseAnAutomobile
{
    void DriveAutomobile()
    {
        IDrivable drivable;
        Automobile myAutomobile = new Automobile();
        str temp;

        myAutomobile = new Automobile();

        if (myAutomobile is IDrivable)
        {
            drivable = myAutomobile;
            drivable.setSpeed(42);
            temp = int2str(drivable.getSpeed());
        }
        else
        {
            temp = "Instance is not an IDrivable.";
        }

        info(temp);
    }
}