Composite Design Pattern
7/1/2016
CS 631: Composite Pattern
1
Outline
• Application
– Portfolios of Instruments
– Design
• Composite Pattern
– Design
– Analysis
– Implementation
7/1/2016
CS 631: Composite Pattern
2
Portfolios
• A financial institution holds a portfolio of securities.
Each portfolio may contain a set of securities as well
as other portfolios.
• Different operations may be performed on any
portfolio/subportfolio:
– Get total balance:
• Add principal on all instruments
– Get portfolio's market value:
• Add present values for all securities
• Example: Fannie Mae Portfolio
7/1/2016
CS 631: Composite Pattern
3
Portfolio Hierarchy Example
FannieMae Portfolio
Assets
Fixed Rate
Mortgages
Mortgage
($100K,
15 year, 6.5%)
7/1/2016
Liabilities
Adjustable Rate
Mortgages
Swap
...
...
CS 631: Composite Pattern
4
Basic Design
• Create classes for different instruments:
– Mortgage
– Bond
– Swap, etc.
• Create a container class:
– Portfolio
• Problem:
– Applications would need to treat Portfolio and Instrument
classes differently.
• Assuming we only need to know the principal and the value of a
portfolio/instrument, they can be treated the same.
• The Composite pattern uses recursive composition so that clients do
not have to make this distinction.
7/1/2016
CS 631: Composite Pattern
5
Composite Pattern
7/1/2016
CS 631: Composite Pattern
6
Composite Design Pattern: Analysis
• Intent
– Compose objects into tree structures to represent part-whole
hierarchies.
• Applicability
– To represent part-whole hierarchies of objects.
– To enable clients to ignore the difference between
compositions of objects and individual objects.
• Clients will treat all objects in the composite structure uniformly.
7/1/2016
CS 631: Composite Pattern
7
Participants
• Component (Security)
– Declares the interface for objects in the composition.
– Implements default behavior.
– Declares an interface for accessing and managing its child
components.
• Leaf (Mortgage, Bond, etc.)
– Represents leaf objects in the composition.
– Defines behavior for primitive objects.
• Composite (Portfolio)
– Defines behavior for components having children.
– Implements child-related operations in the Component
interface.
7/1/2016
CS 631: Composite Pattern
8
Implementation: Security Class
class Security
{
public:
virtual ~Security() {}
virtual double getPrincipal() = 0;
virtual double getValue() = 0;
virtual void add(Security* sec)
{throw "Operation prohibited!";}
virtual Security* getChild(int no)
{
if (no >= this->securities.size())
throw "Child does not exist!";
return this->securities.at(no);
}
protected:
vector<Security*> securities;
};
7/1/2016
CS 631: Composite Pattern
9
Implementation: Mortgage Class
// Leaf class
class Mortgage : public class Security
{
public:
Mortgage(double bal, double r, double t) :
balance(bal), rate(r), term(t) {}
virtual double getPrincipal()
{
return this->balance;
}
protected:
double balance;
double rate;
double term;
};
7/1/2016
CS 631: Composite Pattern
10
Implementation: Portfolio Class
// Composite class
class Portfolio : public class Security
{
public:
virtual double getPrincipal()
{
double sum = 0;
for (i=0; i<this->securities->size(); i++)
sum += this->securities.at(i)->getPrincipal();
return sum;
}
virtual void add(Security* sec)
{
this->securities.push_back(sec);
}
};
7/1/2016
CS 631: Composite Pattern
11