Inheritance

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• Inheritance

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Inheritance

• Reusing code is great
• Inheritance is a great way to reuse code
• Result We want to do inheritance

Super class
Sub class1
Sub class2
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Inheritance

• Inheritance is a mechanism used to design two or
  more classes that are different, but share common
  features
• We start with a class that defines the common
  features the super class
• Then we define classes as extentions of the super
  class the sub classes

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Inheritance

• Defining the super class is just like any other
  class
• public class Band
• int volume
• Instrument InstList
• public Band()
• volume 10
• public void makeNoise( )

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Inheritance

• Each subclass uses the extends clause
• public class RockBand extends Band
• // these do not need to be declared (theyre
  inherited)
• // int volume
• // Instrument InstList
• public RockBand()
• super()
• public void makeNoise( )
• // inside of this is different than in Band

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Inheritance

• Each subclass uses the extends clause
• public class Orchestra extends Band
• // these do not need to be declared (theyre
  inherited)
• // int volume
• // Instrument InstList
• public Orchestra()
• super()
• InstList new Instrument250
• public void makeNoise( )
• // inside of this is different than in Band

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Inheritance

• Several classes can be defined using the same
  base class
• They can have the same data members and slightly
  different functionality
• Or the same functionality with slightly different
  data members
• Or slightly different data members and slightly
  different functionality

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Inheritance

• How are data members and methods inherited?
• If the super class has a public data member or
  method
• Inherited
• If the super class has a protected data member or
  method
• Inherited
• If the super class has private data member
• Not inherited

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Inheritance

• Why use protected?
• From classes that do not inherit from this class,
  protected looks like private.
• Make it visible to only special classes!
• All other normal rules apply for all of these
  variables.

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Inheritance

• Questions???

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Inheritance - Constructors

• public class Base
• public Base()
• System.out.println("Base Class")

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Inheritance - Constructors

• public class DerivedClass extends Base
• public DerivedClass()
• System.out.println("DerivedClass")
• If a call to super() isnt made, its
  automatically inserted at the top of the
  constructor

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Inheritance - Constructors

• public class MoreDerivedClass extends
  DerivedClass
• public MoreDerivedClass()
• System.out.println("MoreDerivedClass")
• public static void main(String args)
• Base c new MoreDerivedClass()
• MoreDerivedClass g new MoreDerivedClass()

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Inheritance - Constructors

• What happens when this main is exectued?
• public static void main(String args)
• Base c new MoreDerivedClass()
• MoreDerivedClass g new MoreDerivedClass()

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Inheritance - Constructors

• What happens when this main is exectued?
• public static void main(String args)
• Base c new MoreDerivedClass()
• MoreDerivedClass g new MoreDerivedClass()
• Base Class
• DerivedClass
• MoreDerivedClass
• Base Class
• DerivedClass
• MoreDerivedClass

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Inheritance

• Questions??

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Inheritance

• Abstract classes and methods
• Often we want to create a super class that
  contains all the common information of subclasses
• But we dont want to create instances of the
  super class
• This type of super class is an abstract class
• It is common for an abstract class to have
  abstract methods that must be implemented by the
  sub classes
• If a class has an abstract method, it must be an
  abstract class