Lecture 10

fall 2018

Narges Norouzi

Introduction to inheritance

Class Hierarchies

Terminology

  • Key points:

    • Inheritance is about hierarchical abstraction

    • Inheritance is about is-a relationship

    • Inheritance is about common attributes

 

Inheritance

Inheritance In java

class implementation

  • Faculty is inherited from Employee

  • How do you implement Employee class?

  • How do you implement Faculty class? 

public class Employee{
    String name;
    double salary;

    String getName(){
        return this.name;
    }
    String getSalary(){
        return this.salary;
    }
    void setName(String name){
        this.name = name;
    }
    void setSalary(double salary){
        this.salary = salary
    }
}
public class Faculty{
    //Employee properties
    String name;
    double salary;
    String getName(){
        return this.name;
    }
    String getSalary(){
        return this.salary;
    }
    void setName(String name){
        this.name = name;
    }
    void setSalary(double salary){
        this.salary = salary
    }

    //Faculty-specific properties
    Course[] courses;
    Course[] getOfferedCourses(){
        return this.courses;
    }
    int getNumOfCourses(){
        return this.courses.length;
    }
}

faculty & employee

  • Faculty is inherited from Employee

  • Faculty extends Employee

  • Attributes and behaviors of Employee will be inherited by Faculty

  • Inheritance provides code reuse

faculty class again

public class Faculty extends Employee{
    /* We will inherit properties of Employee class,
    so there is no need to re-write them here. */
    
    //Faculty-specific properties
    Course[] courses;
    Course[] getOfferedCourses(){
        return this.courses;
    }
    int getNumOfCourses(){
        return this.courses.length;
    }
}

class hierarchy

  • Direct superclass

    • Inherited explicitly (one level up hierarchy)

  • ​Indirect superclass
    • Inherited two or more levels up hierarchy
  • Multiple inheritance
    • Inherits from multiple super classes
  • Java does not support multiple inheritance

 

subclasses may ...

  • Add new functionality New members

  • Use inherited functionality Software reuse

  • Override inherited functionality Change parent methods

  • Zybooks chapters we covered

  • Chapter 10: Inheritance

    • Sections 10.1, 10.2, 10.3, 10.4