AN INTRODUCTION TO INHERITANCE In your group Define

In your group • Define 5 attributes that you would use to describe persons.

What is Inheritance? Generalization vs. Specialization “is a” 11 -3

Inheritance Generalization Insect Contains those attributes and methods that are shared by all insects.

Java keyword, “extends” • We can extend the capabilities of a superclass when we

Inheritance • The subclass inherits fields and methods from the superclass without any of

The Graded. Activity Example Contains those attributes and methods that are shared by all

Inheritance and Constructors • Constructors are not inherited. • When a subclass is instantiated,

The Superclass’s Constructor • The super keyword refers to an object’s superclass. • The

Calling The Superclass Constructor • If a parameterized constructor is defined in the superclass,

Overriding Superclass Methods • A subclass may have a method with the same signature

Overriding Superclass Methods Graded. Activity - score : double + set. Score(s : double)

Preventing a Method from Being Overridden • The final modifier will prevent the overriding

Access Specifiers Access Modifier Accessible to a subclass inside the same package? Accessible to

Chains of Inheritance • A superclass can also be derived from another class. Object

Chains of Inheritance • Classes often are depicted graphically in a class hierarchy. •

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AN INTRODUCTION TO INHERITANCE

In your group • Define 5 attributes that you would use to describe persons. • Define 3 different attributes that can describe students but not persons. • Are there any attributes that define persons but not students? (In other words is there anything that is true of persons that is not true of students as well. )

What is Inheritance? Generalization vs. Specialization “is a” 11 -3

Inheritance Generalization Insect Contains those attributes and methods that are shared by all insects. Specialization Bumble. Bee Contains those attributes and methods that specific to a Bumble Bee. Grasshopper Contains those attributes and methods that are specific to a Grasshopper. 11 -4

Java keyword, “extends” • We can extend the capabilities of a superclass when we make a subclass. Parent Superclass Base class Child Subclass Derived class The child extends the parent 11 -5

Inheritance • The subclass inherits fields and methods from the superclass without any of them being rewritten. • New fields and methods may be added to the subclass. • The Java keyword, extends, is used on the class header to define the subclass. public class Final. Exam extends Graded. Activity 11 -6

The Graded. Activity Example Contains those attributes and methods that are shared by all graded activities. Contains those attributes and methods that are specific to the Final. Exam class. Inherits all non-private attributes and methods from the Graded. Activity class. • Example: – – Graded. Activity. java, Grade. Demo. java, Final. Exam. Demo. java 11 -7

Inheritance and Constructors • Constructors are not inherited. • When a subclass is instantiated, the superclass default constructor is executed first. • Example: – Super. Class 1. java – Sub. Class 1. java – Constructor. Demo 1. java 11 -8

The Superclass’s Constructor • The super keyword refers to an object’s superclass. • The superclass constructor can be explicitly called from the subclass by using the super keyword. • Example: – Super. Class 2. java, Sub. Class 2. java, Constructor. Demo 2. java – Rectangle. java, Cube. Demo. java 11 -9

Calling The Superclass Constructor • If a parameterized constructor is defined in the superclass, – the superclass must provide a no-arg constructor, or • subclasses must provide a constructor, and • subclasses must call a superclass constructor. • Calls to a superclass constructor must be the first java statement in the subclass constructors. 11 -10

Overriding Superclass Methods • A subclass may have a method with the same signature as a superclass method. • The subclass method overrides the superclass method. • This is known as method overriding. • Example: – Graded. Activity. java, Curved. Activity. Demo. java 11 -11

Overriding Superclass Methods Graded. Activity - score : double + set. Score(s : double) : void + get. Score() : double + get. Grade() : char Curved. Activity - raw. Score : double - percentage : double This method is a more specialized version of the set. Score method in the superclass, Graded. Activity. + Curved. Activity (percent : double) + set. Score(s : double) : void + get. Raw. Score() : double + get. Percentage() : double 11 -12

Preventing a Method from Being Overridden • The final modifier will prevent the overriding of a superclass method in a subclass. public final void message() • If a subclass attempts to override a final method, the compiler generates an error. • This ensures that a particular superclass method is used by subclasses rather than a modified version of it. 11 -13

Access Specifiers Access Modifier Accessible to a subclass inside the same package? Accessible to all other classes inside the same package? default (no modifier) Yes Public Yes Protected Yes Private No No Accessible to a subclass outside the package? Access Modifier Accessible to all other classes outside the package? default (no modifier) No No Public Yes Protected Yes No Private No No 11 -14

Chains of Inheritance • A superclass can also be derived from another class. Object Example: Graded. Activity. java Pass. Fail. Exam. Demo. java Graded. Activity Pass. Fail. Exam 11 -15

Chains of Inheritance • Classes often are depicted graphically in a class hierarchy. • A class hierarchy shows the inheritance relationships between classes. Graded. Activity Final. Exam Pass. Fail. Activity Pass. Fail. Exam 11 -16