AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe...
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Transcript of AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe...
![Page 1: AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe persons. Define 3 different attributes that can describe.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f285503460f94c4063e/html5/thumbnails/1.jpg)
An introduction to inheritance
![Page 2: AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe persons. Define 3 different attributes that can describe.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f285503460f94c4063e/html5/thumbnails/2.jpg)
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.)
![Page 3: AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe persons. Define 3 different attributes that can describe.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f285503460f94c4063e/html5/thumbnails/3.jpg)
What is Inheritance?Generalization vs. Specialization
11-3
“is a”
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11-4
Inheritance
Insect
GrasshopperBumbleBee
Contains those attributes and methods that are shared by all insects.
Contains those attributes and methods that specific to a
Bumble Bee.
Contains those attributes and methods that are specific to a
Grasshopper.
Generalization
Specialization
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11-5
Java keyword, “extends”• We can extend the capabilities of a superclass when we make
a subclass.
Parent ChildSuperclass SubclassBase class Derived class
The child extends the parent
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11-6
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 FinalExam extends GradedActivity
![Page 7: AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe persons. Define 3 different attributes that can describe.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f285503460f94c4063e/html5/thumbnails/7.jpg)
11-7
The GradedActivity Example
• Example:– GradedActivity.java,– GradeDemo.java,– FinalExam.java, – FinalExamDemo.java
Contains those attributes and methods that are shared by all graded activities.
Contains those attributes and methods that are specific to the FinalExam
class.Inherits all non-private attributes and methods from the GradedActivity
class.
![Page 8: AN INTRODUCTION TO INHERITANCE. In your group Define 5 attributes that you would use to describe persons. Define 3 different attributes that can describe.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f285503460f94c4063e/html5/thumbnails/8.jpg)
11-8
Inheritance and Constructors
• Constructors are not inherited.
• When a subclass is instantiated, the superclass default constructor is executed first.
• Example: – SuperClass1.java
– SubClass1.java
– ConstructorDemo1.java
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11-9
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:
– SuperClass2.java, SubClass2.java, ConstructorDemo2.java– Rectangle.java, Cube.java, CubeDemo.java
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11-10
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.
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11-11
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: – GradedActivity.java, CurvedActivity.java,
CurvedActivityDemo.java
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11-12
Overriding Superclass Methods
GradedActivity
- score : double
+ setScore(s : double) : void+ getScore() : double+ getGrade() : char
CurvedActivity
- rawScore : double- percentage : double
+ CurvedActivity(percent : double) + setScore(s : double) : void+ getRawScore() : double+ getPercentage() : double
This method is a more specialized version of the setScore method in the superclass, GradedActivity.
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11-13
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.
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11-14
Access SpecifiersAccess Modifier
Accessible to a subclass inside the same package?
Accessible to all other classes inside the same package?
default(no modifier)
Yes Yes
Public Yes Yes
Protected Yes Yes
Private No No
Access ModifierAccessible to a subclass
outside the package?Accessible to all other classes
outside the package?
default(no modifier)
No No
Public Yes Yes
Protected Yes No
Private No No
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11-15
Chains of Inheritance
• A superclass can also be derived from another class. Object
PassFailActivity
PassFailExam
GradedActivity
Example:GradedActivity.javaPassFailActivity.javaPassFailExam.javaPassFailExamDemo.java
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11-16
Chains of Inheritance
• Classes often are depicted graphically in a class hierarchy.
• A class hierarchy shows the inheritance relationships between classes.
PassFailActivity
PassFailExam
GradedActivity
FinalExam