1. Team 13

2. Introduction

 Behavioral design pattern.
 Uses a chain of objects to handle a request.
 Objects in the chain forward the request along the
chain until one of the objects handles the request.
 Avoid coupling the sender of a request to its receiver
by giving more than one object a chance to handle
the request.

3. Class Diagram
 successor
client Handler
Request
handleRequest()
ConcreteHandler1 ConcreteHandler2
handleRequest() handleRequest()

4. Usage

 Several objects have similar methods that could be
appropriate for the action that the program is
requesting.
 One of the objects might be most suitable.

5. Usage (cont.…)

 Having new objects that want to add to the list of
processing options while the program execution.
 When more than one object may handle a request
and the actual handler is not know in advance

6. Implementation

In brief,
 We create four objects that can either “Add”,
“Subtract”, “Multiply” or “Divide”.
 Send two numbers and a command, that allow above
four objects to decide which can handle the
requested calculation.

7. Implementation

 Interface
public interface Chain
{
void calculate(Numbers request);
void setChain(Chain nextChain);
}
}

8. Implementation
 Numbers Class

public class Numbers {
private int _number1, _number2;
private string _command;
public Numbers(int number1, int number2, string command)
{
_number1 = number1;
_number2 = number2;
_command = command;
}
public int getNumber1() { return _number1; }
public int getNumber2() { return _number2; }
public string getCommand() { return _command; }
}
}

9. Implementation
 Addition Class

Public Addition : Chain {
private Chain _nextChain;
public void calculate(Numbers request){
if (request.getCommand() == "add"){
Console.WriteLine(“Result: {0}",request.getNumber1()+request.getNumber2());
}else{ _nextChain.calculate(request);}
}
public void setChain(Chain nextChain){
_nextChain = nextChain;
}
}

10. Implementation
 Subtraction Class

Public Subtraction : Chain {
private Chain _nextChain;
public void calculate(Numbers request){
if (request.getCommand() == "sub"){
Console.WriteLine(“Result: {0}",request.getNumber1()-request.getNumber2());
}else{ _nextChain.calculate(request);}
}
public void setChain(Chain nextChain){
_nextChain = nextChain;
}
}

11. Implementation
 Multiplication Class

Public Multiplication : Chain {
private Chain _nextChain;
public void calculate(Numbers request){
if (request.getCommand() == "mul"){
Console.WriteLine(“Result: {0}",request.getNumber1()*request.getNumber2());
}else{ _nextChain.calculate(request);}
}
public void setChain(Chain nextChain){
_nextChain = nextChain;
}
}

12. Implementation
 Division Class

Public Division : Chain {
private Chain _nextChain;
public void calculate(Numbers request){
if (request.getCommand() == "div"){
Console.WriteLine(“Result: {0}",request.getNumber1()/request.getNumber2());
}else{ “Unidentified Command! Please Check again...”}
}
public void setChain(Chain nextChain){
_nextChain = nextChain;
}
}

13. Implementation
 Demo Class 
class Demo{
public static void Main()
{
Chain chainCalc1 = new Addition();
Chain chainCalc2 = new Subtraction();
Chain chainCalc3 = new Multiplication();
Chain chainCalc4 = new Division();
chainCalc1.setChain(chainCalc2);
chainCalc2.setChain(chainCalc3);
chainCalc3.setChain(chainCalc4);
Numbers request1 = new Numbers(10,5,"add");
Numbers request2 = new Numbers(10,5,"mul");
chainCalc1.calculate(request1);
chainCalc1.calculate(request2);
Console.ReadLine();
}

14. Pros & Cons

 Pros
More efficient
More flexible
Refactor and change the code is easy
 Cons
Handling isn't guaranteed