Chapter10-Object-OrientedProgrammingPolymorphism.ppt

Chapter 10 - Object-Oriented Programming: Polymorphism Chapter 10 - Object-Oriented Programming: Polymorphism 10.1 Introduction Polymorphism “Program in the general” Treat objects in same class hierarchy as if all superclass objects Abstract class Common functionality Makes programs extensible New classes added easily, can still be processed In our examples Use abstract superclass Shape Defines common interface (functionality) Point, Circle and Cylinder inherit from Shape Class Employee for a natural example 10.2 Relationships Among Objects in an Inheritance Hierarchy Previously (Section 9.4), Circle inherited from Point Manipulated Point and Circle objects using references to invoke methods This section Invoking superclass methods from subclass objects Using superclass references with subclass-type variables Subclass method calls via superclass-type variables Key concept subclass object can be treated as superclass object “is-a” relationship superclass is not a subclass object 10.2.1 Invoking Superclass Methods from Subclass Objects Store references to superclass and subclass objects Assign a superclass reference to superclass-type variable Assign a subclass reference to a subclass-type variable Both straightforward Assign a subclass reference to a superclass variable “is a” relationship HierarchyRelationshipTest1.javaLine 11Assign superclass reference to superclass-type variableLine 14 Assign subclass reference to subclass-type variableLine 17Invoke toString on superclass object using superclass variableLine 22Invoke toString on subclass object using subclass variable 1 // Fig. 10.1: HierarchyRelationshipTest1.java 2 // Assigning superclass and subclass references to superclass- and 3 // subclass-type variables. 4 import javax.swing.JOptionPane; 5 6 public class HierarchyRelationshipTest1 { 7 8 public static void main( String[] args ) 9 { 10 // assign superclass reference to superclas