An interface specifies the externally visible operations of a class, component, package, or other element without specifying internal structure.
An interface has operations but no attributes, states, or associations. In terms of notation, an interface can be represented in two ways:
As a class shape with the stereotype <<interface>> attached to the element that supports it by a realizes relationship.
By a circle attached to the element that supports it by a solid line.
A realizes relationship is a relationship that means the client at the tail of the arrow supports or inherits all the operations of the supplier at the arrowhead. Use realizes relationships between a class (as the supplier) and its interface (when the interface is represented by a class shape with the stereotype <<interface>>), or between an implementation class (as the supplier) and a type.
Change which shape displays for an interface
Right-click the Interface shape and click Show as Class-like Interface or Show as Lollipop Interface.
Name an Interface shape and add other property values
Open the element's UML Properties dialog box by double-clicking the icon that represents the element in the tree view or the shape that represents the element in a diagram.
Control which property values display on a shape in a diagram by right-clicking the shape, and then clicking Shape Display Options. In the UML Shape Display Options dialog box, select and clear options to display or hide property values.
Control which property values are displayed on the Interface shape
Right-click the shape, click Shape Display Options, and then select or clear options to show or hide values.
Navigate to other views of the interface
Right-click the shape, click Views, select the view you want, and then click OK.
Show, in a view, the relationships between the interface and other elements
Right-click the shape, and then click Show Relationships.
Change the size of the circle at the end of the linear Interface shape
Drag the control handle .