Dynamic and Distributed Scheduling in Communication Networks and Manufacturing Systems

1
Applying Inheritance to Solve problems
2
Classification, Generalization and Specialization

• Classification
• the act of identifying and categorizing similar
  objects into classes is known as classification
• the resulting categories are known as classes
  which form meaningful abstractions for organizing
  information

List of people objects in a furniture shop
3
Classification, Generalization and Specialization

• People in Furniture Shop

4
Classification, Generalization and Specialization

• Generalization
• generalization is the act of capturing
  similarities between classes and defining the
  similarities in a new generalized class
• the original classes are known as subclasses, and
  the generalized class is known as superclass

Employee
superclass
5
Classification, Generalization and Specialization

• Specialization
• specialization is the act of capturing
  differences among objects in a class and creating
  new distinct subclasses with the differences

PeopleInFS
Employee
subclass
6
Classification, Generalization and Specialization

• Super- and sub-classes can be organized into a
  class hierarchy with the superclasses placed
  toward the top of the hierarchy and the
  subclasses toward the bottom of the hierarchy
• which class an object is referred to in a class
  hierarchy is a matter of generality

superclass
PeopleInFS
superclass and subclass
Customer
Employee
SalesPerson
Manager
Secretary
subclass
7
Inheritance Example People in Furniture Shop
name getName( )
PeopleInFS
name address budget getName( ) getBudget(
) placeOrder( )
name employeeNum getName( ) getEmployeeNum()
Customer
Employee
name employeeNum commission getName(
) getEmployeeNum( ) getCommission( ) takeOrder( )
SalesPerson
Manager
Secretary
8
Inheritance Example People in Furniture Shop
PeopleInFS
- name String getName( ) String
inherits from (or is-a )
Customer
Employee
- address String - budget int getBudget( )
int placeOrder( ) void
- employeeNum int getEmployeeNum( ) int
SalesPerson
Manager
Secretary
- commission int getCommission( )
int takeOrder( ) int
- allowance int getAllowance( ) int
9
Inheritance Example People in Furniture Shop
SalesPerson
Employee
getCommission( ) int takeOrder( ) int
PeopleInFS
getName( ) String
- name String
getEmployeeNum( ) int
- employeeNum int
- commission int
10
Inheritance and Java Classes/Interfaces
subclass or derived class
superclass or base class
extends
extends
subinterface
superinterface
implements
class
interface
11
Applied Inheritance

• Decide on the classes involved from the problem
  description
• Group classes into conceptually equivalent groups
• Per group of classes, the generalizing concept
  will be a Parent to those classes
• Distribute responsibilities amongst all classes
  based on what is appropriate and customary for
  that class
• Example A program to teach geometry needs to
  model some basic shapes
• All shapes have surface area, could have volume
  and location
• The shapes that need to be modeled are Circle,
  Rectangle, Sphere, Cylinder, and a Square
• What classes will you need?

12
A Geometry Example
Classes Circle, Rectangle, Sphere, Cylinder,
Square, Coordinate
All Shapes
2D Shapes
Circle
Sphere
Coordinate
Rectangle
Group classes
Cylinder
Square
Square is a Rectangle
3D Shapes
Inheritance hierarchy
13
A Geometry Example
Distribute Responsibilities
Shape getSurfaceArea() clone() equals() toStr
ing() Object getLocation()
Shape3D getVolume()
Shape2D ?
Is Shape2D needed?
14
Example Abstract classes
public abstract class Shape double
getSurfaceArea() Object getLocation()
Object clone() String toString()
boolean equals()
Observe the syntax of Shape The methods are not
virtual methods

• Abstract Class A class with at least one
  unimplemented method
• Interface A class with only unimplemented methods

.
public interface Shape double
getSurfaceArea() Object getLocation()
Object clone() String toString()
boolean equals()
15
Sample Interfaces
Q How do you inherit from an interface? A By
implementing the interface
public interface Shape implements Cloneable
... public abstract class Shape2D implements
Shape ...
Q How do you inherit from an Abstract class? A
The usual way, by extending
public class Circle extends Shape2D
16
Its All Still Inheritance!
public interface Shape extends Clonable
public abstract class Shape2D implements
Shape public class Circle extends
Shape2D

• Circle has to implement all
• unimplemented methods of
• 2DShape
• Shape
• Clonable

17
Its All Still Inheritance!
Client Code Circle c new Circle() Shape s
c Cloneable cln s Shape2D s2d s
Through c you can access ALL methods of Circle
AND its parents!
Through s you can access ONLY methods of Shape
and Cloneable implemented in Circle
Through cln you can access ONLY methods of
Cloneable implemented in Circle
Through s2d you can access ONLY methods of Shape,
Cloneable, and Shape2D implemented in Circle
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The Class Rectangle
public class Rectangle extends Shape2D private
int width,length public Rectangle(int w,int
l) width w length l public
int getSurfaceArea() return(widthlength)

19
The Class Rectangle
public boolean equals(Object o) if(!o
instanceOf Rectangle) return false
Rectangle r (Rectangle)o if (this.width !
r.width) return false if
(this.length!r.length) return false
return true
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The Class Rectangle
public void toString() System.out.println(Rect
anglewidth length) public Object
clone() return(new Rectangle(width,length) p
ublic Object getLocation()
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The Class ShapePair
public abstract class ShapePair extends Shape
private Shape shape1,shape2 public
ShapePair(Shape s1,Shape s2) shape1 s1
shape2 s2 public int getSurfaceArea()
return(shape1.getSurfaceArea()
shape2.getSurfaceArea())
22
The Class Rectangle
public Object clone() Shape s1
(Shape)shape1.clone() Shape s2
(Shape)shape2.clone() return(new
ShapePair(s1,s2)

• A very simple example of grouping two shapes!

23
Understanding Polymorphism

• Static vs dynamic binding
• binding refers to the association of a method
  invocation and the code to be executed on behalf
  of the invocation
• in static binding, all the associations are
  determined at compile time
• conventional function calls are statically bound
• char shapeTypenumShapes
• struct circle circlesnumCircles
• struct square squaresnumSquares
• int c 0, s 0
• ...
• for (i 0 i lt numShapes i)
• switch (shapeTypei)
• c calculateCircleArea(circlesc) break
• s calculateSquareArea(squaress) break

24
Understanding Polymorphism

• in dynamic binding, the code to be executed in
  response to a method invocation (i.e., a message)
  will not be determined until runtime
• method invocations to variable shapeArray (in the
  following example) are dynamically bound

public class ShapeDemoClient public static
void main(String argv ) Circle c1 new
Circle("Circle C1") Circle c2 new
Circle("Circle C2", 3.0f) Square s1 new
Square("Square S1") Square s2 new
Square("Square S2", 3.0f) Shape shapeArray
c1, s1, c2, s2 for (int i 0 i lt
shapeArray.length i)
System.out.println("The area of "
shapeArrayi.getName( ) " is "
shapeArrayi.calculateArea( ) " sq. cm.")
// End main // End ShapeDemoClient1 class
25
Avoid Confusion Between Is-A and Has-A

• Improper class hierarchies are commonly created
  when designers confuse is-a with has-a
• is-a relation the extension creates a new
  class that is kind of the original class, e.g,
• has-a relation an object of one class uses
  objects of other classes to store state or do
  work
• A vehicle is-a Movable Abstraction
• A vehicle is-a Physical Abstraction
• A vehicle has-a location
• A vehicle is-not-a Point (the class of location)

Rectangle
Square
1

circle
point
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Composition versus Inheritance

• All aspects of the protocol are part of childs
  interface
• Requires us to explicitly send messages to the
  class
• Restricts operations on child to those that are
  applicable
• Creates an independent type
• Makes the use of the parent structure an
  implementation detail that can easily be changed

• Requires us to look at the parents as well as
  childs protocol
• Reuses the parents code with no explicit
  references
• Allows all the parent operations to be applied,
  even those that are meaningless for the child
• Allows us to use the child anywhere the parent
  can be used
• Ties the child to choice of the parent structure

27
BankAccount hierarchy
We will write thisclass later
Object
BankAccount
JointBankAccount
Every Java class inherits from the top level
Object class.The Object class is the ultimate
parent of every Java class
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BankAccount Examples

• Declare two accounts
• BankAccount fred new
• BankAccount(123, "Fred", 345.50)
• JointBankAccount fredMary new
• JointBankAccount(345, "Fred", "Mary", 450,65)
• A joint account is a type of account
• BankAccount ellenFrank new
• JointBankAccount(456, "Ellen", "Frank", 3450)
• The following statement is illegal
• JointBankAccount fred new
• BankAccount(123, "Fred", 345.50)

29
BankAccount Examples

• Consider the two accounts
• JointBankAccount fredMary new
• JointBankAccount(345, "Fred", "Mary", 450,65)
• BankAccount ellenFrank new
• JointBankAccount(456, "Ellen", "Frank", 3450)
• The following statements are legal
• String owner fredMary.getOwner()
• String jointOwner fredMary.getJointOwner()
• The 2nd statement is illegal
• String owner fredMary.getOwner()
• String jointOwner ellenFrank.getJointOwner()

30
AccountReader Example

• Problem Write an AccountReader class that can
  read both BankAccount and JointBankAccount
  objects.
• Suggests that we need two methods with prototypes
• public BankAccount readBankAccount()
• public JointBankAccount readJointBankAccount()
• Because of polymorphism only the first version is
  needed a joint account "is an" account.

31
AccountReader Example

• package booklib
• import booklib.BankAccount
• import booklib.JointBankAccount
• import booklib.KeyboardReader
• public class AccountReader
• private KeyboardReader input
• new KeyboardReader()
• public BankAccount readAccount() ...

32
AccountReader Example

• public BankAccount readAccount()
• // declare local vars
• // read account type
• // read number, balance, owner
• if (type 2)
• // read joint owner name
• return new JointBankAccount(...)
• else
• return new BankAccount(...)

it's also aBankAccount
33
AccountReaderTester

• import booklib.
• public class AccountReaderTester
• public AccountReaderTester()
• AccountReader accountInput new
• AccountReader()
• BankAccount a accountInput.readAccount()
• System.out.println(a)
• public static void main(String args)
• new AccountReaderTester()

34
toString is polymorphic

• The print statement System.out.println(a)is
  shorthand for System.out.println(a.toString())
  
• the Java run-time system knows whether a refers
  to a BankAccount object or to a JointBankAccount
  object so it calls the correct version of the two
  toString methods

35
Bank Account Processing

• Problem Read an array of BankAccount objects and
  process them in several ways.
• Reading the array is common to all processors
• Therefore we start with an abstract account
  processor class that has a non-abstract method to
  do the account reading and provides an abstract
  method for account processing
• Each subclass will provide its own implementation
  of the processor method.

36
AccountProcessor

• abstract public class AccountProcessor
• private AccountReader inputAccount
• new AccountReader()
• protected KeyboardReader console
• new KeyboardReader()
• protected BankAccount account
• public void readAccounts()...
• abstract public void processAccounts()

subclasses willneed to accessthem
semi-colonis necessary
keyword to indicate abstract classes and methods
37
readAccounts Method

• public void readAccounts()
• System.out.println("How many accounts?")
• int size input.readInt()
• account new BankAccountsize
• for (int k 0 k lt account.length k)
• accountk inputAccount.readAccount()

38
MaxBalanceProcessor

• public class MaxBalanceProcessor
• extends AccountProcessor
• public void processAccounts()
• double max account0.getBalance()
• for (int k 1 k lt account.length k)
• double b accountk.getBalance()
• if (b gt max) max b
• System.out.println
• "The maximum balance is " max)

implement theprocessAccountsmethod
39
MaxBalanceProcessorRunner

• public class MaxBalanceProcessorRunner
• public static void main(String args)
• MaxBalanceProcessor program
• new MaxBalanceProcessor()
• program.readAccounts()
• program.processAccounts()

calls method inAccountProcessor
40
A Fund Transfer Method

• Problem Write a method that can be used to
  transfer a given amount from one bank account to
  another that works with both BankAccount and
  JointBankAccount objects
• Without polymorphic types we would need four
  different methods to cover the four possible
  types of transfer (bank to bank, joint to joint,
  bank to joint and joint to bank)
• With polymorphism only one method is needed

41
A Fund Transfer Method

• public void transfer(BankAccount from,
• BankAccount to, double amount
• boolean ok from.withdraw(amount)
• if (ok)
• to.deposit(amount)
• This works because a JointBankAccount "is a"
  BankAccount

42
Using the Method

• BankAccount fred new BankAccount(...)
• BankAccount joan new BankAccount(...)
• JointBankAccount fredMary
• new JointBankAccount(...)
• JointBankAccount joanBob
• new JointBankAccount(...)
• transfer(fred, joan, 89.55)
• transfer(fred, fredMary, 49.35)
• transfer(joanBob, fredMary, 100.00)
• transfer(joanBob, joan, 50.00)

43
Employee Hierarchy
Everything commonto all employees
Employee
Manager
HourlyWorker
PartTimeWorker
These differ onlyin how the salaryis calculated
CommissionWorker
44
Abstract Employee Class

• abstract public class Employee
• private String name
• public Employee(String name)
• this.name name
• public String getName()
• return name
• abstract public double grossSalary()
• abstract public double netSalary()

Constructor forthe name part
polymorphicmethods
45
Subclasses

• Manager
• gross monthly salary,10 deductions.
• HourlyWorker
• gross monthly salary from hours worked and hourly
  wage, 5 ideductions.
• PartTimeWorker
• as above with not deductions
• CommissionWorker
• like manager with a commission as a percentage of
  monthly sales

46
The Manager Class

• public class Manager extends Employee
• protected double gross
• protected double net
• public Manager(String name, double salary)
• super(name)
• gross salary
• net 0.9 gross
• public double grossSalary() return gross
• public double netSalary() return net
• public String toString() ...

call superclassconstructor todo its part
47
ProcessEmployees

• public Employee staff
• ...
• public void doCalculations()
• totalGrossSalary totalNetSalary 0.0
• for (int k 0 k lt staff.length k)
• totalGrossSalry staffk.grossSalary()
• totalNetSalary staffk.netSalary()
• System.out.println(staffk)
• totalBenefits
• totalGrossSalary - totalNetSalary

a polymorphic loop
48
What is an Adapter Class?

• Inheritance always adds functionality.
• Sometimes we need to subtract functionality.
• For example we may want to make a class serve a
  more specific or simpler purpose by hiding some
  of its methods.
• Adapter classes use composition to do this.
• Our custom format class is an example hiding the
  complexity of the DecimalFormat class.

49
The java.util.Vector class

• This is a generic dynamic container class. Some
  of its constructors and methods are
• public Vector()
• public Vector(int initialCapacity)
• public void addElement(Object obj)
• public Object elementAt(int k)
• public void setElementAt(int k)
• public int size()
• // convert vector to an Object array
• public Object toArray()
• // convert to array of specified type
• public Object toArray(Object obj)

50
Vector with BankAccount

• Storing BankAccount objects in a Vector container
• Vector v new Vector()
• v.addElement(new BankAccount(123,"Fred",345.50)
• v.addElement(new BankAccount(345,"Mary",435.43)
• System.out.println(v.elementAt(0))
• System.out.println(v.elementAt(1))
• BankAccount b (BankAccount) v.elementAt(0)

Object amnesiaagain
51
Vector with BankAccount

• Converting a Vector to an array
• Vector v new Vector(1000)
• ...
• BankAccount a new BankAccountv.size()
• a (BankAccount) v.toArray(a)

Object amnesiaagain
52
BankAccountVector Class

• package booklib
• import java.util.Vector
• public class BankAccountVector
• private Vector v // composition (hide it)
• public BankAccountVector() ...
• public BankAccountVector(int initialCap)...
• public void addAccount(BankAccount b) ...
• public BankAccount getAccount(int k) ...
• public void replaceAccount(BankAccount b,
• int k) ...
• public int size() ...
• public BankAccount toArray() ...

53
BankAccountVector Class

• Constructors
• public BankAccountVector()
• v new Vector()
• public BankAccountVector(int initialCap)
• v new Vector(initialCapacity)

54
BankAccountVector Class

• Methods
• public void addAccount(BankAccount b)
• v.addElement(b)
• public BankAccount getAccount(int k)
• return (BankAccount) v.elementAt(k)

55
BankAccountVector Class

• Methods
• public void replaceAccount(BankAccount b, int k)
• v.setElementAt(b,k)
• public int size()
• return v.size()
• public BankAccount toArray()
• BankAccount b new BankAccountv.size()
• return (BankAccount) v.toArray(b)

56
A Harder Example

• A Stack Machine is a device that lets you write
  simple programs that use a Stack
• Items (in our example numbers) are placed on and
  removed from the stack using two commands push
  to place on, and pop to take off
• Items are always placed on top of the stack and
  taken off the top of the stack
• A stack is a last-in-first-out structure
• Arithmetic operations can be performed by
  assuming that the two operands needed for the
  operation will be the top two items on the stack
  and the answer will be placed back on the stack

57
A Harder Example
push 5
add
push 10
10
15
5
5
Stack
Stack
Stack
Any mathematical expression can be converted into
a series of machine instructions
push 5 push 4 subtract push 6 multiply push
5 add print
5 (6 (5 - 4))
58
A Harder Example
public static void main(String args)
StackMachine sm new StackMachine()
sm.load(programFileName) sm.run()
Clients view
What are the classes?
StackMachine Coordinate all operations void
load(String fileName) void run()
ProgramLoader Its purpose is to read the program
in void load(String filename) void String
getInstruction(int i) int numInstructions()
Stack Its purpose is to model
the Stack idea void push(double value) double
pop()
59
Example gaining an understanding
example.stk push 5 push 4 subtract push
6 multiply push 5 add print
public class StackMachine ProgramLoader pl
Stack stack public StackMachine() pl
new ProgramLoader() stack new Stack()
public void load(String fileName)
pl.load(fileName) public void run()
String instruction for(int i0 iltpl.
numInstructions() i) instruction
pl.get(i) System.out.println(instruction)

Client code public static void main(String
args) StackMachine sm new StackMachine()
sm.load(example.stk) sm.run()
What happens here?
60
Implementing the instructions First Solution
public class StackMachine ... public void
run() String instruction for(int
i0 iltpl.numInstructions() i)
instruction pl.get(i) StringTokenizer st
new StringTokenizer(instruction) String
command st.nextToken() if
(command.toUpperCase(PUSH) String
parameter st.nextToken()
stack.push(Double.parseDouble(parameter))
else if (command.toUpperCase(PRINT)
double d stack.pop()
System.out.println(d) ...
Messy, long, yuck,
61
Implementing the instructions Better Solution

• Think of instruction as classes and group them

instructions
Organized by number of parameters
pop
divide
add
push
subtract
print
multiply
one parameter instruction
no parameter instruction
Organized by function
arithmetic instructions
instructions
multiply
stack instructions
divide
add
push
subtract
pop
utility instructions
print
62
Implementing the instructions Better Solution
Instruction
OneParameterInstruction
NoParameterInstruction
push
pop
add
multiply
divide
subtract
print
Instruction
ArithmeticInstruction
UtilityInstruction
StackInstruction
push
pop
add subtract divide multiply
print

• Each instruction will know how to execute
  itself
• Each instruction will know how to initialize
  itself

63
Implementing the instructions Better Solution
public class StackMachine ... public void
run() String instruction for(int
i0 iltpl.numInstructions() i)
instruction pl.get(i) StringTokenizer st
new StringTokenizer(instruction) String
command st.nextToken() try Instruction
instRef (Instruction)
Class.forName(command)).newInstance()
instRef.load(st) instRef.execute(stack)
catch(Exception e)
System.out.println(Syntax error bad
instruction) System.exit(0)

Client code public static void main(String
args) StackMachine sm new StackMachine()
sm.load(example.stk) sm.run()
64
Implementing the instructions Better Solution
public interface Instruction public void
load(StringTokenizer) public void
execute(Stack)
public abstract class ArithmeticInstruction
implements Instruction public void
load(StringTokenizer st)
public class Add extends ArithmeticInstruction
public void execute(Stack stack)
double operand1 stack.pop() double
operand2 stack.pop()
stack.push(operand1operand2)
65
Implementing the instructions Better Solution
public interface Instruction public void
load(StringTokenizer) public void
execute(Stack)
public abstract class StackInstruction implements
Instruction // only here for design
completeness
public class PopInstruction extends
StackInstruction public void
load(StringTokenizer st) public void
execute(Stack stack) stack.pop()
public class PushInstruction extends
StackInstruction double value public void
load(StringTokenizer st) String parameter
st.nextToken() value Double.parseDouble(par
ameter) public void execute(Stack stack)
stack.push(value)