03-inheretance java code programming .pdf

03-inheretance java code programming .pdf

• 1.
  Inheritance 61
• 2.
  Java Programming: OOP 62 Inheritance •On the surface, inheritance is a code re-use issue. – we can extend code that is already written in a manageable manner. • Inheritance is more, it supports polymorphism at the language level! • Information is made manageable in a hierarchical order
• 3.
  Inheritance cont. • WithInheritance, new class can be derived from existing classes as a building block • New class Inherit properties and methods from the existing class • New class can also added Its own properties and methods • Keyword – Extends – Implements 63
• 4.
  Java Programming: OOP 64 Inheritancecont. • Take an existing object type (collection of fields and methods) and extend it. – create a special version of the code without re- writing any of the existing code (or even explicitly calling it!). – End result is a more specific object type, called the sub-class / derived class / child class. – The original code is called the super class / parent class / base class.
• 5.
  Example 7/11/2015 Budditha Hettige(budditha@yahoo.com) 65 Student University Student Undergraduate Post graduate Employee Phone Employee ----------------- - Name Email Phone FulltimeEmployee ------------------------ Salary Office Manager Manager ------------------ CompanyCar Email Phone Contractor ------------------ HourlyRate, ContractDuration
• 6.
  66 Introduction (Cont.) • Classhierarchy – Direct superclass • Inherited explicitly (one level up hierarchy) – Indirect superclass • Inherited two or more levels up hierarchy – Single inheritance • Inherits from one superclass – Multiple inheritance • Inherits from multiple superclasses
• 7.
  Inheritance 67 Animal Dog public class Animal { } publicclass Dog extends Animal { }
• 8.
  Introduction (Cont.) 68 Animal Dog Animal Dog Private Public Public
• 9.
  69 protected protected protected protected Members • protectedaccess – Intermediate level of protection between public and private – protected members accessible by • superclass members • subclass members • Class members in the same package – Subclass access to superclass member • Keyword super and a dot (.)
• 10.
  Introduction (Cont.) 70 Animal Dog Animal Dog Private Public Public Protected Protected
• 11.
  Example 71
• 12.
  IS-A Relationship (Example) publicclass Animal { } public class Mammal extends Animal { } public class Reptile extends Animal { } public class Dog extends Animal { } 72 Animal Mamal extends
• 13.
  IS-A Relationship (Example) publicclass Dog extends Mammal { public static void main(String args[]) { Animal a = new Animal(); Reptile r = new Reptile(); Mammal m = new Mammal(); Dog d = new Dog(); System.out.println(m instanceof Animal); System.out.println(d instanceof Mammal); System.out.println(d instanceof Animal); } } 73 Animal Mamal Dog Reptile
• 14.
  IS-A Relationship • InObject Oriented terms following are true: – Animal is the superclass of Mammal class. – Animal is the superclass of Reptile class. – Mammal and Reptile are sub classes of Animal class. – Dog is the subclass of both Mammal and Animal classes. 74
• 15.
  IS-A Relationship • IS-Arelationship we can say: – Mammal IS-A Animal – Reptile IS-A Animal – Dog IS-A Mammal – Hence : Dog IS-A Animal as well • Use of the extends keyword the subclasses will be able to inherit all the properties of the superclass except for the private properties of the superclass 75
• 16.
  Java Programming: OOP 76 Accessingsuper class methods • Can use super() to access all (non-private) super class methods. – even those replaced with new versions in the derived class. • Can use super() to call base class constructor.
• 17.
  Java Programming: OOP 77 SingleInheritance • You can't extend more than one class! – the derived class can't have more than one base class. • You can do multiple inheritance with interface inheritance.
• 18.
  Java Programming: OOP 78 InheritanceExample cont. • Employee: name, email, phone – FulltimeEmployee: also has salary, office, benefits, … • Manager: CompanyCar, can change salaries, rates contracts, offices, etc. – Contractor: HourlyRate, ContractDuration, … • A manager a special kind of FullTimeEmployee, which is a special kind of Employee. • The relationship modeled by inheritance is often referred to as a “is a” relationship
• 19.
  Inheritance Example 79 Employee ------------------ Name Email Phone FulltimeEmployee ------------------------ Salary Office Manager Manager ------------------ CompanyCar Email Phone Contractor ------------------ HourlyRate, ContractDuration
• 20.
  Inheritance Example 80 Employee ------------------ Name Email Phone FulltimeEmployee ------------------------ Salary Office Manager Manager ------------------ CompanyCar Email Phone Contractor ------------------ HourlyRate, ContractDuration Is a Isa Is a
• 21.
  Example 7/11/2015 Budditha Hettige(budditha@yahoo.com) 81
• 22.
  Example 7/11/2015 Budditha Hettige(budditha@yahoo.com) 82
• 23.
  Example 7/11/2015 Budditha Hettige(budditha@yahoo.com) 83