Realization EEE321'07

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RealizationEEE321.07
Royal Military College of Canada Electrical and
Computer Engineering
Refs Ambler Ch 5Booch Ch 1

• Maj JW Paul
• Jeff.Paul_at_rmc.ca
• 1-613-541-6000 x6656

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There are 10 kinds of people in the world.Those
who understand binary,
and those who dont...
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Review

• What is Polymorphism?
• Greek appearing in many forms
• What is overloading?
• meaning based on context
• method signature
• operators
• What is overriding?
• sub-type conversion

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Overriding

• Using a method with the same signature (which
  means?) but in a different way in a different
  class
• The distinction is based on how the object is
  called
• Dynamic binding (at runtime)

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Example of Overriding
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Polymorphism
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An example

• Geometric objects

square
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Restriction in Java

• If a method overrides a superclass method, it is
  not permitted to have a lower access level in the
  subclass than it does in the superclass JLS
  8.4.6.3

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Parametric Polymorphism

• Depends on type of the call parameter at the time
  of the execution of the program.
• A very powerful feature
• Does not exist in Java
• C has templates

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Power of Polymorphism
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Polymorphic
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Good Programming

• Minimize access to classes and methods
• Priority
• Private
• Package (aka Friendly)
• Protected
• Public
• Public access should be very rare

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Restriction in Java

• If a method overrides a superclass method, it is
  not permitted to have a lower access level in the
  subclass than it does in the superclass JLS
  8.4.6.3

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Abstract Classes

• Definition

An Abstract Class can never be implemented (no
objects will be instantiated directly from this
class)
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Abstract vs Concrete Class

• An abstract class can have methods and attributes
• If an abstract class has only methods, what is
  it?
• An interface

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Interface

• An interface is a variation of an abstract class
• all the methods are abstract (what does this
  mean)
• defines only static final member variables
• We do not inherit from interfaces, we realize
  them
• Useful as it allows Java programmer to simulate
  multiple inheritance

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Uses of Interfaces

• Revealing an objects programming interface
  without revealing actual body of the class.
• Capturing similarities between unrelated classes
  without forcing a class relationship
• Describing "function-like" objects that can be
  passed as parameters to methods invoked on other
  objects
• We say that the the implementation of a class is
  hidden behind the interface

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Interface in UML
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Interface in UML (alternate)
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Interface in UML
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Implementation in Java
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Another Example
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Inheritance vs Realization
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Abstract Class vs Interface

• Abstract Class
• only instantiated by a subclass
• may contain implemented methods
• may contain abstract methods.
• may contain attributes.

• Interface
• implemented by another class
• may not contain implemented methods
• may contain method signatures
• may only contain constants (static, final)

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Factory Method
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Pattern Factory Method

• Factory Method gives the responsibility of
  creating instances to the sub class
• Use when
• The class does not know in advace what type of
  object it must create
• The class wants the sub-class to specify what
  type of object needs to be created
• Allows one to decouple the product and the
  producer

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Factory Method General Structure
Creator
Product
factoryMethod()
...
anOperation()
product factoryMethod()
...
ConcreteCreator
constructor
ConcreteProduct
...
factoryMethod()
return new ConcreteProduct
...
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Factory Method example
create
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Factory Method Java
Remarquer le type de retour est Document et non
ascii.
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Good Programming

• Use Factory Method instead of the regular
  constructor Effective Java - item 1.

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Review

• Why is Polymorphism Important?