Abstract Classes and Interfaces (?) June 21, 2017 Reading Quiz - - PowerPoint PPT Presentation

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Abstract Classes and Interfaces (?) June 21, 2017 Reading Quiz - - PowerPoint PPT Presentation

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Abstract Classes and Interfaces (?) June 21, 2017 Reading Quiz Abstract Classes A. Abstract classes inherit from multiple parents, standard classes only inherit from one parent. B. Abstract classes can only have one instance at a time,

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Abstract Classes and Interfaces (?)

June 21, 2017

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Reading Quiz

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Abstract Classes

  • A. Abstract classes inherit from multiple parents,

standard classes only inherit from one parent.

  • B. Abstract classes can only have one instance at a time,

standard classes can have any number.

  • C. Abstract classes cannot be directly instantiated,

standard classes can be directly instantiated

  • D. Abstract classes can only contain primitive properties,

standard classes can have primitive and reference properties.

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Abstract Methods

  • A. Abstract classes consist of only abstract methods
  • B. Abstract methods do not specify their

implementation

  • C. Abstract methods are the same thing as a "static

final" method

  • D. Abstract methods perform faster than standard

methods

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Interfaces vs. Abstract Classes

  • A. Interfaces always inherit from Abstract Classes
  • B. Abstract Classes always implement Interfaces
  • C. Interfaces cannot inherit from Abstract Classes
  • D. Abstract Classes cannot implement Interfaces
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Whats the Result?

  • A. "Child💕Person"
  • B. "Person💕Child"
  • C. "null💕null"
  • D. Won't compile
  • E. Runtime error

abstract class Person { public String name() { return "Person";
 }
 } class Child extends Person { public String name() { return "Child";
 }
 } Child aKindChild = new Child(); Person aMeanPerson = new Person(); System.out.println(
 aMeanPerson.name() + "💕 " + aKindChild.name()
 );

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Whats the Result?

  • A. "🐲"
  • B. "🐷"
  • C. "" (ie empty string)
  • D. Won't compile
  • E. Runtime error

interface Emojier { public String asEmoji(); } class Dog implements Emojier { public String asEmoji() { return "🐷 ";
 }
 } class Cat implements Emojier { public String asEmoji() { return "🐲 ";
 }
 } Cat toonces = new Cat(); String anEmoji = toonces.asEmoji(); System.out.println(anEmoji);

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Done!

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Housekeeping

  • Piazza Recap / Java environments
  • Homework 2 questions
  • Homework 3 incoming
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Abstract Classes

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Problem

  • Types express a Taxonomy and data / functionality
  • Some types are meant to represent data in a

program

  • Some types are "only" categorization
  • Code should enforce this distinction
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Animals Mammals Reptiles Dogs Whales Snakes Lizards isWarmBlooded() -> true isWarmBlooded() -> false

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Animals Mammals Reptiles Dogs Whales Snakes Lizards isWarmBlooded() -> true isWarmBlooded() -> false

Categorization <– –> Program Logic

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Animals Mammals Reptiles Dogs Whales Snakes Lizards isWarmBlooded() -> true isWarmBlooded() -> false

Categorization <– –> Program Logic

Abstract

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Java Solution:
 Abstract Classes

  • Can not be instantiated, but can be inherited
  • Standard inheritance model
  • Arbitrarily deep
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Animals Mammals Whales Dogs Sad Dogs Kujo Old Yeller

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Animal Mammals Whale Dog SadDog DeadDog JerkDog

Which are Valid?

  • A. new Mammal()
  • B. new SadDog()
  • C. new Dog()
  • D. new JerkDog()
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Abstract Use Cases?

Abstract Concrete Subtype(s) 1 SimpsonCharacter Bart, Lisa 2 AdminUser StandardUser, AnonymousUser 3 MembersOfTheRamones JoeyRamone, TommyRamone 4 CreditCardChargeError RareCreditCardChargeError

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Animal.java –>

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Abstract Methods

  • Taxonomy can impose "helpful" restrictions too
  • Things below me must implement these methods
  • Keep types clean
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Fur.java –>

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Interfaces

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Problem

  • Classes categorize data in a single, global way
  • Multiple categorizations possible
  • Redundancy, or insane hierarchies
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TrickyTypes.md –>

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Entertainment Live Recorded Opera Performance Jazz Performance Books Photographs Whirly Ball Records

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Entertainment Live Recorded Opera Performance Jazz Performance Books Photographs Whirly Ball Records

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Entertainment Live Recorded Opera Performance Jazz Performance Books Photographs Whirly Ball Vinyl void record(? item);

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Java Solution

  • Interfaces
  • Hierarchical, but separate
  • Same modifiers, same inheritance rules
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Interfaces vs. Classes

  • Classes for data
  • Animals
  • Music Categories
  • Movies
  • Interfaces for Functionality
  • Pet-able
  • Danceable
  • Recordable
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Interfaces.java –>

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Interfaces Specifics

  • Classes can implement multiple interfaces
  • ArrayList implements Serializable, Iterable,

Collection, List

  • Small, light
  • Similar to Abstract Classes
  • Inheritance, default methods
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Taxonomizing File Types

  • /etc/mime.types
  • Mime is a very simple taxonomy system
  • Lets implement in code!