INTRODUCTION TO JAVA PROGRAMMING教学（华南理工）review-upcasting 4.pptVIP

OOPData abstraction, Inheritance Polymorphism Data abstraction Inheritance Polymorphism Polymorphism pitfall private methods Fields static methods Only non-private methods may be overridden Any field accesses are resolved by the compiler, are not polymorphic. If a method is static, it doesnt behave polymorphically. Static methods are associated with the class, not the individual objects. constructors Order of constructor calls public class Sandwich extends PortableLunch { static { System.out.println(Sandwich block); } private Bread b = new Bread(); private Cheese c = new Cheese(); private Lettuce l = new Lettuce(); public Sandwich() { System.out.println(Sandwich()); } public static void main(String[] args) { new Sandwich(); } } Meal block Lunch block Portable block Sandwich block Lettuce block Bread block Cheese block Cheese() Bread() Lettuce() Meal() Cheese() Lunch() PortableLunch() Cheese() Bread() class Cheese { static { System.out.println(Cheese block); } Cheese() {System.out.println(Cheese()); } } class Lettuce { static { System.out.println(Lettuce block); } private Bread b = new Bread(); Lettuce() { System.out.println(Lettuce()); } } class Bread { static { System.out.println(Bread block); } private Cheese c = new Cheese(); Bread() { System.out.println(Bread()); } } class Lunch extends Meal { static { System.out.println(Lunch block); } private Cheese c = new Cheese(); Lunch() { System.out.println(Lunch()); } } class PortableLunch extends Lunch { static { System.out.println(Portable block); } PortableLunch() { System.out.println(PortableLunch());} } class Meal { static { System.out.println(Meal block); } private Lettuce l = new Lettuce(); Meal() { System.out.println(Meal()); } } Cheese() * method method A Hierarchy from Generic to Specific class Employe