First we look at a standard Dos based application

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Combining Decorator Factory Patterns
First we look at a standard Dos based application
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Combining Decorator Factory Patterns
class Account private int balance public
Account(int b)
balanceb public Account(Account acc)
balanceacc.balance public int
read_bal() return
balance public void deposit(int amt)
balance amt public void withdraw(int
amt) balance -amt
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public class Ex1 public static void Main()
Account a new Account(20) int
choice1,amt0 string temp
while(choice!4) Console.WriteLine() Console
.WriteLine("1 Deposit") Console.WriteLine("2
Withdraw") Console.WriteLine("3 Read
Bal") Console.WriteLine("4 Exit") Console.W
rite("Enter Choice")
tempConsole.ReadLine()
choiceConvert.ToInt32(temp)
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switch(choice) case 1 Console.Write("Enter
Amount ") tempConsole.ReadLine()

amtConvert.ToInt32(temp) a.deposit(amt)
break case 2 Console.Write("Enter Amount
")
tempConsole.ReadLine() amtConvert.ToInt32(temp)

a.withdraw(amt) break case
3 int ba.read_bal()
Console.WriteLine("Balance"b)
break
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During Testing Phase
- we introduce trace printouts public void
deposit(int amt)Cosole.WriteLine("deposit()")
balance amt
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class Account private int balance public
Account(int b)
balanceb public Account(Account acc)
balanceacc.balance public int
read_bal() Console.WriteLine(read_bal()")
return
balance public void deposit(int amt)
Console.WriteLine(deposit()")
balance
amt public void withdraw(int amt)
Console.WriteLine(
withdraw()")
balance -amt
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Unsatisfactory

• Must be removed after testing
• What if you need to retest later
• Different test phases my require different types
  of traces

Alternative Solution using Decorator Pattern
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UML Class Diagram
Account
Decorator
Account
SafeAcc
TestAcc
DecTest
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Combining Decorator Factory Patterns
class Account private int balance public
Account(int b)
balanceb public Account(Account acc)
balanceacc.balance public int
read_bal() return
balance public void deposit(int amt)
balance amt public void withdraw(int
amt) balance -amt
As Before
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Combining Decorator Factory Patterns
class Decorator Account protected Account
account public Decorator(Account
acc)base(acc) accountacc
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class TestAcc Decorator public
TestAcc(Account acc)base(acc) new public
int read_bal() print("read_bal()")
return account.read_bal() new
public void deposit(int amt)print("deposit()")

account.deposit(amt) new public void
withdraw(int amt) print("withdraw()")
account.withdraw(amt)
public void print(String s)
Console.WriteLine(s)
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public class Ex1 public static void Main()
TestAcc a new TestAcc(new Account(20))
int choice1,amt0 string temp
while(choice!4) Console.WriteLine() Console
.WriteLine("1 Deposit") Console.WriteLine("2
Withdraw") Console.WriteLine("3 Read
Bal") Console.WriteLine("4 Exit") Console.W
rite("Enter Choice")
tempConsole.ReadLine()
choiceConvert.ToInt32(temp)
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Trace Printout
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After Testing we change back
public class Ex1 public static void Main()
Account a new Account(20) int
choice1,amt0
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We can create other decorators

• Safe Account
• Seeks confirmation before Deposit, Withdraw

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class SafeAcc Decorator public
SafeAcc(Account acc)base(acc)
new public int read_bal()
Console.Write("Enter 1 to confirm ")
string tempConsole.ReadLine()
int choiceConvert.ToInt32(temp)
if (choice1) return
account.read_bal() else
return 0
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new public void deposit(int amt)
Console.Write("Enter 1 to confirm ")
string tempConsole.ReadLine()
int choiceConvert.ToInt32(temp)
if (choice1)
account.deposit(amt) new public void
withdraw(int a)
Console.Write("Enter 1 to confirm ")
string tempConsole.ReadLine()
int choiceConvert.ToInt32(temp)
if (choice1) account.withdraw(a)

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After Testing we change back
public class Ex1 public static void Main()
SafeAcc a new SafeAcc(new Account(20))
int choice1,amt0
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Confirmation Requested
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Can combine these
public class Ex1 public static void Main()
Account acnew Account(20) TestAcc a
new TestAcc(new SafeAcc(null,ac),ac)
int choice1,amt0
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Trace Printout and Confirmation Requested
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Can combine these
public class Ex1 public static void Main()
Account acnew Account(20) SafeAcc a
new SafeAcc(new TestAcc(null,ac),ac) int
choice1,amt0
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Confirmation Requested then Trace Printout
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To achieve this we must modify code of decorators
class TestAcc Decorator private
SafeAcc sacc public TestAcc(SafeAcc
sacc,Account acc)base(acc)
this.saccsacc new public int
read_bal() print("read_bal()") if
(sacc!null) return sacc.read_bal()
else return account.read_bal()
new public void deposit(int amt)print("deposit()"
) if (sacc!null)
sacc.deposit(amt) else
account.deposit(amt)
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class SafeAcc Decorator private
TestAcc tacc public SafeAcc(TestAcc
tacc,Account acc)base(acc)
this.tacctacc new public int read_bal()
Console.Write("Enter 1 to
confirm ") string
tempConsole.ReadLine() int
choiceConvert.ToInt32(temp)
if (tacc!null) return tacc.read_bal()
else return account.read_bal()
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new public void deposit(int amt)
Console.Write("Enter 1 to confirm ")
string tempConsole.ReadLine()
int choiceConvert.ToInt32(temp)
if (tacc!null) tacc.deposit(amt)
else account.deposit(amt)
new public void withdraw(int amt)
Console.Write("Enter 1 to confirm ")
string tempConsole.ReadLine()
int choiceConvert.ToInt32(temp)
if (tacc!null)
tacc.withdraw(amt) else
account.withdraw(amt)
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Can add functionality by adding objects
Options

• 1. Account a new Account(bal)
• 2. SafeAcc a new SafeAcc(null,new
  Account(20))
• Or alternative
• Account acnew Account(20)
• SafeAcc a new SafeAcc(null,ac)
• TestAcc a new TestAcc(null,new Account(20))
• Account acnew Account(20)
• TestAcc a new TestAcc(new
  SafeAcc(null,ac),ac)

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Improve by using Factory Pattern
Factory creates an Account object based on data
In the following example base choice on user
input Better solution would be to read value
from a configuration file Could change the value
in file after test etc First We must make some
minor changes to introduce Polymorphism

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using System abstract class Decorator
Account protected Account account public
Decorator(Account acc)base(acc)
accountacc class AccInterface virtual
public int read_bal()return 0 virtual public
void deposit(int amt) virtual public void
withdraw(int amt)
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using System abstract class Decorator
Account protected Account account public
Decorator(Account acc)base(acc)
accountacc class AccInterface virtual
public int read_bal()return 0 virtual public
void deposit(int amt) virtual public void
withdraw(int amt)
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class AccountAccInterface private int
balance public Account(int b)
balanceb public Account(Account acc)
balanceacc.balance override
public int read_bal() return
balance override public void deposit(int
amt) balance
amt override public void withdraw(int amt)
balance -amt

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class TestAcc Decorator private
SafeAcc sacc public TestAcc(SafeAcc
sacc,Account acc)base(acc)
this.saccsacc override public int
read_bal() print("read_bal()") if
(sacc!null) return sacc.read_bal()
else return account.read_bal()
override public void deposit(int
amt)print("deposit()") if
(sacc!null) sacc.deposit(amt)
else account.deposit(amt) etc
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Now we can use Polymorphism to get the same result
public class Ex1 public static void Main()
Account acnew Account(20)
AccInterface a new TestAcc(new
SafeAcc(null,ac),ac) int
choice1,amt0 etc
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Now we can use a Factory to decide type of Account
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public class Ex1 public static void Main()
Console.WriteLine("Enter Account Type")
Console.WriteLine("1 Normal")
Console.WriteLine("2 Test")
Console.WriteLine("3 Safe")
Console.WriteLine("4 Safe and Test")
Console.Write("Enter Choice")
string tConsole.ReadLine() int
optionConvert.ToInt32(t) AccInterface a
AccountFactory.createAccou
nt(20,option) int
choice1,amt0 (as
before)
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class AccountFactory static public AccInterface
createAccount(int bal,int type) Account acnew
Account(bal) if (type1) return ac if
(type2) return new TestAcc(null,ac) if
(type3) return new SafeAcc(null,ac) else
return new TestAcc(new
SafeAcc(null,ac),ac)

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Input to Factory
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Could also have a Factory Based on a single
parameter
public class Ex1 public static void Main()
Console.Write("Enter Balance")
string tConsole.ReadLine() int
balConvert.ToInt32(t) AccInterface a
AccountFactory.createAccount(bal) int
choice1,amt0
(as before)
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class AccountFactory static public
AccInterface createAccount(int bal) if (bal
lt 100) return new Account(bal) else return
new SafeAcc(null,new Account(bal))

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Exercise1 Given the class class
Counter private int value public Counter(int
v)valuev public Counter(Counter cc)
valuecc.value public int read_value()return
value public void increment()value public
void decrement()
value-- Now we want to decorate the Counter
(similar to Account Ex)
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(i) class UpperLimit extends Decorator same as
before except increment will only increment if
value lt20 otherwise will print out Too High
Hint public void increment()if
(counter.read_value()lt20) (ii) class LowerLimit
extends Decorator same as before except
decrement will only decrement if value
gt0 otherwise will print out Too Low (iii)
Want a factory to decide on the of counter
See next Dos screen
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Exercise 1(b) Now Modify the Application so the
Factory is based on just an initial counter value
read in from the Console - Values lt 5 will
generate a Normal Counter Object - 5-10 inclusive
will generate a LowerLimit Object - 11 -15 an
UpperLimit Object - Values gt 15 will produce one
with both an Upper Lower Limit
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Exercise2 Given the class class
Display private String name public
Display(String n)namen public Display(Display
dd) namedd.name public void
print()System.out.println("\t"name) public
void setName(String n)namen Will Display a
name Now we want to decorate the Display
(similar to Account Ex)
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Normal Display Athlone UpperLine

Athlone LowerLine Athlone
Upper and Lower Line
Athlone

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(a) class UpperLine extends Decorator print a
line of before name (b) class LowerLine
extends Decorator print a line of after
name (c) Want a factory to decide on the of
Display Type See next Dos screen
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