classDiagram
  class Shape {
    <<abstract>>
    +draw() void
  }
  class Circle {
    +radius int
    +draw() void
  }
  Shape <|-- Circle
---
+--------------+    
| <<abstract>> |    
| Shape        |    
+--------------+    
|              |    
+--------------+    
| +draw: void  |    
+--------------+    
        ^           
        |           
        |           
+--------------+    
| Circle       |    
+--------------+    
| +int: radius |    
+--------------+    
| +draw: void  |    
+--------------+