the superclass/base class object reference is used to call the target method. a subclass object reference is assigned to a superclass/base class object reference. all subclasses override the target method. To use polymorphism, these conditions must be true: the classes are in the same hierarchy. A base-class object is not an object of any of its derived classes. The is-a relationship applies from a derived class to its direct and indirect base classes, but not vice versa. An object of a derived class can be treated as an object of its base class. ĩ Polymorphic Behavior In a method call on an object, the type of the actual referenced object, not the type of the reference, determines which method is called. To refresh the screen, the screen manager periodically sends each object the same message-namely, Draw, while each object responds in its own unique way. A screen-manager application maintains a collection (e.g., a SpaceObject array) of references to objects of the various classes. Each class inherits from the common base class SpaceObject, which contains method Draw. Īs another example, suppose we design a video game that manipulates objects of many different types, including objects of classes Martian, Venusian, Plutonian, SpaceShip and LaserBeam. The polymorphism occurs when an application invokes a method through a base-class variable. These operations also can be performed on other Quadrilaterals, such as Squares, Parallelograms and Trapezoids. Any operation that can be performed on a Quadrilateral object can also be performed on a Rectangle object. If class Rectangle is derived from class Quadrilateral, then a Rectangle is a more specific version of a Quadrilateral.
#Swift downcast vs cast code#
Only client code that instantiates new objects must be modified to accommodate new types.
#Swift downcast vs cast software#
Software that invokes polymorphic behavior is independent of the object types to which messages are sent. ĥ Polymorphism Polymorphism promotes extensibility. Ĥ Introduction Polymorphism enables you to write applications that process objects that share the same base class in a class hierarchy as if they were all objects of the base class.
To determine an object’s type at execution time. How polymorphism makes systems extensible and maintainable. Lecture 8 Polymorphism and Type Casting CSE 1322 ģ OBJECTIVES The concept of polymorphism and how it enables you to “program in the general.” To use overridden methods to effect polymorphism.
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