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Strategy pattern.pdf
1. Class report
CLASS ASSIGNMENT- 1
WAR PLANNING
(STRATEGY PATTERN)
Submitted by:
Md.Mahedi Mahfuj -BIT 0207
Submitted to:
Maeenul Islam
Lecturer,IIT
Institute of Information Technology
University of Dhaka
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2. Class report
War Planning:
Introduction:
At first, we have to see what happens when a war is being undertaken in
certain circumstances, i.e. what features we have to focus on.
Actually, the war is called by the king of a certain region. He commands the
commander of the battalion under whom a huge number of soldiers are
working all the time.
Now, let’s see the entire war through technical perspectives. Before, going
through the scenario, we have to know what a client code is.
Client Code:
The part of the code that controls the behavior of the other classes is known
as the client code of those classes. As an instance,
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3. Class report
War {
Main () {
Commander cm = new commander ();
Soldier s1 = new soldier ();
Soldier s2 = new soldier ();
Soldier s3 = new soldier ();
cm. AddSoldier(s1);
cm. AddSoldier(s2);
cm. AddSoldier(s3);
cm. StartWar();
}
}
So, we can see that this client code Main () can control both commanders and
soldiers. So, the Main() function here plays the role of the King.
Now, let’s see what can be in the commander part :
Commander:
Name:-
Command:-
Command();
Soldierlist;
AddSoldier(soldier s);
Soldierlist.add (s ) {
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4. Class report
StartWar () {
S1.Changemode (“Aggression”);
S2.Changemode (“Defensive”);
S3.Changemode (“Aggression”);
…….
……..
……..
………
}
And, in the soldier part:
Soldier:
Name:-
Mode:-
Function:-
Fight ();
Changemode ();
…..
…..
……
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5. Class report
Now, let’s see what we mostly do in such cases:
Soldier{
Changemode (String m)
{
Mode=m; //mode change
Fight ();
}
Fight ()
{
//according to mode, fight now.
If(mode=”Aggressive”)
{
…………
…………//about 1000 line code
………….
}
Else if (mode=”Defensive”)
{
………….
………….//about 1000 line code again
…………..
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6. Class report
}}
Problems:
Now, let’s see what the problems are that we may face in solving in the above
mentioned way:
At first,
If we add some more fighting modes like neutral, some only carrying
foods & weapons etc then we have to add all such things in the same class
soldier. Hence, the soldier class will eventually become huge which is not
suitable for handling a good code.
Then,
If we separate the modes into distinguished classes, then another
problem will arise, ambiguity.
The modes will be described in three different functions by three
different programmers who contributed in coding the codes of three different
classes namely soldier, aggressive & defensive respectively.
Then,
If we keep the mode as string/integer , then for every change in
different fighting modes, we have to change in soldier class also which is not
expected at all.
Solution:
Let’s troubleshoot the problems mentioned above:
For solving the first problem,
We have to separate the fighting modes into
classes & then all possible changes in modes will be done in the specific
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7. Class report
classes. So, The coder of soldier will not be disturbed for any change in the
fighting mode.
Class Aggressive{
}
Class Defensive{
}
Class Mode3{
}
Class ……..
……..
……..
………
In this way, we can add different modes as much as possible whenever
needed.
Now, let’s troubleshoot the second problem.
For troubleshooting that,
We have to fix a specific function & every class should be made bound to use
that specific function. For this we can declare an interface & every class should
implement that interface.
Interface Ifight {
Fight();}
Class Aggressive implements Ifight {
Fight () {
Print (“I am fighting in aggressive mode”) ;}}
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8. Class report
Class Defensive implements Ifight{
Fight () {
Print (“I am fighting in defensive mode”) ;
}
Class Mode3 implements Ifight{
Fight () {
Print (“I am fighting in neutral mode”) ;
}
Class Mode4 implements Ifight{
……………
……………
……………
So, every class here is bound to use the function fight().So, three different
coders coding three different classes do not have to depend on each other.
Now,another question may come…..Why are we using an interface, not an
abstract class?
The very answer is;
In an abstract class there can be an abstract method, a defined method
and variables as well.But,here we only have to declare a function,that’s
all.So, we have no need to declare an abstract class,only an interface is
enough,i.e. minimal. For this very reason, we have used an interface
instead of using an abstract class.
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9. Class report
Now,let’s fix the third problem.
If we keep modes as string/integer then such problems will arise often. So, it
is better to use the modes as object. Only then, such problems will never
happen in near future.
Like, in the commander class we can use the modes as objects.
Commander Class:
S1.Changemode (new Aggressive())
…..
…….
…….
S1.Changemode (new Defensive())
……..
……..
………
S1.Changemode (new Mode3())
………
………
………
This use of modes as object has made the code more flexible & well-
maintained.
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10. Class report
Main Code Sample:
Hence, the main code should have the following structure:
War Class:
War {
Main () {
Commander cm = new commander ();
Soldier s1 = new soldier ();
Soldier s2 = new soldier ();
Soldier s3 = new soldier ();
cm. AddSoldier(s1);
cm. AddSoldier(s2);
cm. AddSoldier(s3);
cm. StartWar();
}
StartWar () {
S1.Changemode (“Aggression”);
S2.Changemode (“Defensive”);
S3.Changemode (“Aggression”);
…….
……..
……..
}}
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12. Class report
Defensive Class:
Class Defensive implements Ifight{
Fight () {
Print (“I am fighting in defensive mode”) ;
}}
Mode3 Class:
Class Mode3 implements Ifight{
Fight () {
Print (“I am fighting in neutral mode”) ;
}}
Mode4 Class:
………
………
………
Commander Class:
S1.ChangeMode (new Aggressive())
………
………
………
S1.Changemode (new Defensive())
……..
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13. Class report
……..
………
S1.Changemode (new Mode3())
………
………
In this way, we can easily diminish all the problems that we have faced earlier.
This way of solving a problem is known as “Strategy Pattern”.
……………………………………………………………………………..X…………………………………………………………………………………
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