Computer Science A
  • Introduction
  • Overview
  • Course at a Glance
  • Course Exam and Description
  • Quick Reference Sheet
  • Unit 1 Primitive Types
    • 1.1 Why Programming? Why Java?
    • 1.2 Variables and Data Types
    • 1.3 Expressions and Assignment Statements
    • 1.4 Compound Assignment Operators
    • 1.5 Casting and Ranges of Variables
  • Unit 2 Using Objects
    • 2.1 Objects: Instances of Classes
    • 2.2 Creating and Storing Objects (Instantiation)
    • 2.3 Calling a Void Method
    • 2.4 Calling a Void Method with Parameters
    • 2.5 Calling a Non-void Method
    • 2.6 String Objects: Concatenation, Literals, and More
    • 2.7 String Methods
    • 2.8 Wrapper Classes: Integer and Double
    • 2.9 Using the Math Class
  • Unit 3 Boolean Expressions and if Statements
    • 3.1 Boolean Expressions
    • 3.2 if Statements and Control Flow
    • 3.3 if-else Statements
    • 3.4 else if Statements
    • 3.5 Compound Boolean Expressions
    • 3.6 Equivalent Boolean Expressions
    • 3.7 Comparing Objects
  • Unit 4 Iteration
    • 4.1 while Loops
    • 4.2 for loops
    • 4.3 Developing Algorithms Using Strings
    • 4.4 Nested Iteration
    • 4.5 Informal Code Analysis
  • Unit 5 Writing Classes
    • 5.1 Anatomy of a Class
    • 5.2 Constructors
    • 5.3 Documentation and Comments
    • 5.4 Accessor Methods
    • 5.5 Mutator Methods
    • 5.6 Writing Methods
    • 5.7 Static Variables and Methods
    • 5.8 Scope and Access
    • 5.9 this Keyword
    • 5.10 Ethical and Social Implications of Computing Systems
  • Unit 6 Array
    • 6.1 Array Creation and Access
    • 6.2 Traversing Arrays
    • 6.3 Enhanced for Loop for Arrays
    • 6.4 Developing Algorithms Using Array
  • Unit 7 ArrayList
    • 7.1 Introduction to ArrayList
    • 7.2 ArrayList Methods
    • 7.3 Traversing ArrayLists
    • 7.4 Developing Algorithms Using ArrayLists
    • 7.5 Searching
    • 7.6 Sorting
    • 7.7 Ethical Issues Around Data Collection
  • Unit 8 2D Array
    • 8.1 2D Arrays
    • 8.2 Traversing 2D Arrays
  • Unit 9 Inheritance
    • 9.1 Creating Superclasses and Subclasses
    • 9.2 Writing Constructors for Subclasses
    • 9.3 Overriding Methods
    • 9.4 super Keyword
    • 9.5 Creating References Using Inheritance Hierarchies
    • 9.6 Polymorphism
    • 9.7 Object Superclass
  • Unit 10 Recursion
    • 10.1 Recursion
    • 10.2 Recursive Searching and Sorting
  • Free Response Questions
    • 2021
    • 2022
    • 2023
    • 2024
  • Code
    • Week 1
    • Week 2
    • Week 3
    • Week 4
    • Week 5
    • Week 6
    • Week 7
    • Week 8
    • Week 9
    • Week 10
    • Week 11
    • Week 12
    • Week 13
    • Week 14
    • Week 15
    • Week 16
    • Week 17
    • Week 18
    • Week 19
    • Week 20
    • Week 21
    • Week 22
    • Week 23
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  • Learning Objective
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  1. Unit 9 Inheritance

9.5 Creating References Using Inheritance Hierarchies

Enduring Understanding

When multiple classes contain common attributes and behaviors, programmers create a new class containing the shared attributes and behaviors forming a hierarchy. Modifications made at the highest level of the hierarchy apply to the subclasses.

Learning Objective

Define reference variables of a superclass to be assigned to an object of a subclass in the same hierarchy.

Essential Knowledge

When a class S “is-a” class T, T is referred to as a superclass, and S is referred to as a subclass.

If S is a subclass of T, then assigning an object of type S to a reference of type T facilitates polymorphism.

If S is a subclass of T, then a reference of type T can be used to refer to an object of type T or S.

Declaring references of type T, when S is a subclass of T, is useful in the following declarations:

§ Formal method parameters § arrays — T[] var ArrayList<T> var

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