Polymorphism

1
Polymorphism
2
Static vs. Dynamic Binding

• Binding
• The determination of which method in the class
• hierarchy is to be used for a particular object.
• Static (Early) Binding
• When the compiler can determine which method in
  the
• class hierarchy to use for a particular object.
• Dynamic (Late) Binding
• When the determination of which method in the
  class
• hierarchy to use for a particular object occurs
  during
• program execution.

3
Static Binding

• Compiler can determine
• For example,
• Time t1
• ExtTime et2
• t1.Set() // static binding
• et1.Set() // static binding
• t1.Write() // static binding
• et1.Write() // static binding

4
Dynamic Binding

• Compiler cannot determine binding of object to
  method
• Binding is determined dynamically at runtime
• To indicate that a method is to be bound
  dynamically,
• must use the reserved word virtual
• virtual void Write() // dynamic binding
  will occur
• When a method is defined as virtual, all
  overriding methods
• from that point on down the hierarchy must be
  defined as
• virtual
• A pure virtual method is defined as
• virtual void Write() const 0
• When a class contains a pure virtual method, the
  class is
• truly abstract I.e., it cannot be instantiated

5
Static vs. Dynamic Binding Example
Class Attributes
Methods Shape - virtual
computeArea - virtual computeVolume
- pure virtual printShapeName
- pure virtual
print Point x - virtual
printShapeName y -
virtual print - constructor
- setPoint - getX -
getY Circle radius - virtual
printShapeName -
virtual print - virtual computeArea
- setRadius - getRadius
- constructor Cylinder height - virtual
printShapeName - virtual print
- virtual computeArea - virtual
computeVolume -
setHeight - getHeight - constructor

6
Static vs. Dynamic Binding Example (cont)
void virtualViaPointer(const Shape) void
virtualViaReference(const Shape ) void main()
Point point(7, 11) Circle circle(3.5,
22, 8) Cylinder cylinder(10, 3.3, 10, 10)
point.printShapeName() // static
binding point.print() cout ltlt endl //
static binding circle.printShapeName()
// stataic binding circle.print() cout ltlt
endl // static binding cylinder.printShape
Name() // static binding
cylinder.print() cout ltlt endl // static
binding
7
Static vs. Dynamic Binding Example (cont)
Shape arrayOfShapes3 // array of base
class pointers arrayOfShapes0 point
arrayOfShapes1 circle arrayOfShapes2
cylinder for (int I 0 I lt 3 I)
virtualViaPointer(arrayShapesI) for (int j
0 j lt 3 j) virtualViaReference(arraySh
apesj)
8
Static vs. Dynamic Binding Example (cont)
void virtualViaPointer(const Shape
baseClassPtr) // Dynamic binding takes
place baseClassPtr-gtprintShapeName()
baseClassPtr-gtprint() cout ltlt Area ltlt
baseClassPtr-gtcomputeArea() ltlt endl ltlt
Volume ltlt baseClassPtr-gtcomputeVolume()
ltlt endl
9
Static vs. Dynamic Binding Example (cont)
void virtualViaReference(const Shape
baseClassRef) // Dynamic binding takes
place baseClassRef.printShapeName()
baseClassRef.print() cout ltlt Area ltlt
baseClassRef.computeArea() ltlt endl ltlt
Volume ltlt baseClassRef.computeVolume()
ltlt endl