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Inheritance Review

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Inheritance

  • A relationship between classes

Inheritance

  • A relationship between classes
  • Super class - more generalized type

Inheritance

  • A relationship between classes
  • Super class - more generalized type
    • Animal

Inheritance

  • A relationship between classes
  • Super class - more generalized type
    • Animal
  • Sub classes - more specific types of the super class

Inheritance

  • A relationship between classes
  • Super class - more generalized type
    • Animal
  • Sub classes - more specific types of the super class
    • Dog
    • Gnat
    • Robin

Inheritance

  • A relationship between classes
  • Super class - more generalized type
    • Animal
  • Sub classes - more specific types of the super class
    • Dog
    • Gnat
    • Robin
  • Sub class is-a super class

Motivation for Inheritance

  • Code reuse

Motivation for Inheritance

  • Code reuse
  • Identify similar but not identical types

Motivation for Inheritance

  • Code reuse
  • Identify similar but not identical types
  • Use general reference to point to specific object type

JavaFX Button UML

  • Open triangle signifies inheritance (points to super class)

JavaFX Button UML

Code reuse

  • Properties managed by Control:
    • contextMenu
    • skin
    • toolTip
  • Properties managed by Labeled:
    • font
    • graphic
    • lineSpacing
    • etc...
  • Properties managed by ButtonBase:
    • armed
    • onAction

Benefits of Inheritance

Identifying similar but not identical types

  • Separator, MenuBar, Labeled, ScrollPane, ListView, and ToolBar are all specific types of Controls

Benefits of Inheritance

Identifying similar but not identical types

  • Separator, MenuBar, Labeled, ScrollPane, ListView, and ToolBar are all specific types of Controls

General ref can point to specific object type

Control control = new Separator();
Labeled labeledControl = new Label("I'm an enigma");
ButtonBase button = new Button("I'm not a dress shirt");
button = new CheckBox("I don't play hockey");
control = button;
button = labeledControl; // <-- Illegal since a labeled control may not be a button

Analogies

  • I can refer to my daughter as my child
  • I can refer to my maternal grandfather as my ancestor
  • I can refer to my iPhone 8 plus as my cell phone or just phone

Jokes explained

  • An enigma - defies labeling
  • A shirt - needs to be pressed (ironed)
  • Hockey - I don't want to get hurt by being checked

Code Reuse

javafx.scene.control.Control
    javafx.scene.control.Labeled
        javafx.scene.control.ButtonBase
            javafx.scene.control.Button
  • Functionality shared by all objects that are Controls is implemented in the Control class

Code Reuse

javafx.scene.control.Control
    javafx.scene.control.Labeled
        javafx.scene.control.ButtonBase
            javafx.scene.control.Button
  • Functionality shared by all objects that are Controls is implemented in the Control class
    • E.g., setToolTip()

Code Reuse

javafx.scene.control.Control
    javafx.scene.control.Labeled
        javafx.scene.control.ButtonBase
            javafx.scene.control.Button
  • Functionality shared by all objects that are Controls is implemented in the Control class
    • E.g., setToolTip()
  • Functionality shared by all objects that are Labeled controls is implemented in the Labeled class

Code Reuse

javafx.scene.control.Control
    javafx.scene.control.Labeled
        javafx.scene.control.ButtonBase
            javafx.scene.control.Button
  • Functionality shared by all objects that are Controls is implemented in the Control class
    • E.g., setToolTip()
  • Functionality shared by all objects that are Labeled controls is implemented in the Labeled class
    • E.g., setText()

Code-Reuse Classes

  • It may make sense to create a super class solely to promote code reuse

Code-Reuse Classes

  • It may make sense to create a super class solely to promote code reuse
  • The ButtonBase class exists solely for code reuse

Code-Reuse Classes

  • It may make sense to create a super class solely to promote code reuse
  • The ButtonBase class exists solely for code reuse
    • All buttons (buttons, hyperlinks, checkboxes, radio buttons, etc...) need to respond to actions
    • ButtonBase manages what code should be run when the button is pressed
    • Classes with Base or Abstract in the name are typically created to promote "code reuse"

Synonyms

  • Super class ↔ Parent class
  • Sub class ↔ Child class
  • B extends A ↔ B derives from A ↔ B is a sub class of A

Inheritance

  • A relationship between classes
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