The concept of interface is that we have a set of behavior that an
implementing class is supposed to provide, after which we can use all
such classes and their objects similarly as we know that the behavior is
available.
For example, if we have a Drawable interface that defines a method
draw(), then if our Player class and our Ball class both implement the
interface, we can add them to an array of Drawable and just send the
array to the paint method to draw.
The keyword interface is used like
interface SomeInterface
{
void aMethod();
…
}
and when implemented, something like
class SomeClass implements SomeInterface
{
void aMethod();
…
}