oop programming

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Sharon said:
Hi all,

I have a logical oop problem; I have an interface, and derived classes

The interface represents a general printer, and each class is a specific
printer



The question is what is the correct way to get a new instance of a printer
by its name?

Where should the getPrinterObject function be?
Click to expand...

You have a separate PrinterFactory object that can return a reference to the
correct type.
 
Hi all,

I have a logical oop problem; I have an interface, and derived classes

The interface represents a general printer, and each class is a specific
printer



The question is what is the correct way to get a new instance of a printer
by its name?

Where should the getPrinterObject function be?







Example:





ifPrinter printerObj = getPrinterObject("EpsonP333");



printDocument.setDocument(d1);

printerObj.printDocument();





interface IfPrinter
{
void printDocument();

void rollEmptyPage();

void cleanPrinterHead();
string getPrinterType();

}



class Hpv40 : IfPrinter

{
public void printDocument(){

do Hpv40 printing ...

}

public string getPrinterType(){ return this.type;}
}

class EpsonP333 : IfPrinter

{
public void printDocument(){

do EpsonP333 printing ...

}

public string getPrinterType(){ return this.type;}

}

class Cannon512: IfPrinter

{
public void printDocument(){

do Cannon512 printing ...

}

public string getPrinterType(){ return this.type;}

}
 
Sharon said:
shuld i add new PrinterFactory class ?
Yes.

how do i implement it ?
Click to expand...

Depends on what you're trying to accomplish in the long term. Generally,
you'd have the factory look up the right thing to instantiate, but look up
from where is the main question. Perhaps just a case statement. But maybe
you want something more dynamic, so you could have it load a new assembly
from disk.

So, generally, it's:

1. Receive request for creation of specific type.
2. Find specific type.
3. Create new instance of specific type.
4. Return new instance (via interface).
--
Reginald Blue
"I have always wished that my computer would be as easy to use as my
telephone. My wish has come true. I no longer know how to use my
telephone."
- Bjarne Stroustrup (originator of C++) [quoted at the 2003
International Conference on Intelligent User Interfaces]
 
Sharon said:
so it will be somthing like :
Click to expand...
<code elided>

Yup, that's the factory pattern.

--
Reginald Blue
"I have always wished that my computer would be as easy to use as my
telephone. My wish has come true. I no longer know how to use my
telephone."
- Bjarne Stroustrup (originator of C++) [quoted at the 2003
International Conference on Intelligent User Interfaces]
 
so it will be somthing like :


ifPrinter printerObj = PrinterFactory.getPrinterObject("EpsonP333");
printDocument.setDocument(d1);
printerObj.printDocument();


class PrinterFactory{

public IfPrinter getPrinterObject(string printerName){
if(printerName.equels("Hpv40")
return new Hpv40();
else if(printerName.equels("EpsonP333")
return new EpsonP333();

.....
}

}


interface IfPrinter
{
void printDocument();

void rollEmptyPage();

void cleanPrinterHead();
string getPrinterType();

}



class Hpv40 : IfPrinter

{
public void printDocument(){

do Hpv40 printing ...

}

public string getPrinterType(){ return this.type;}
}

class EpsonP333 : IfPrinter

{
public void printDocument(){

do EpsonP333 printing ...

}

public string getPrinterType(){ return this.type;}

}

class Cannon512: IfPrinter

{
public void printDocument(){

do Cannon512 printing ...

}

public string getPrinterType(){ return this.type;}

}











Reginald Blue said:
Sharon said:
shuld i add new PrinterFactory class ?
Yes.

how do i implement it ?
Click to expand...

Depends on what you're trying to accomplish in the long term. Generally,
you'd have the factory look up the right thing to instantiate, but look up
from where is the main question. Perhaps just a case statement. But
maybe
you want something more dynamic, so you could have it load a new assembly
from disk.

So, generally, it's:

1. Receive request for creation of specific type.
2. Find specific type.
3. Create new instance of specific type.
4. Return new instance (via interface).
--
Reginald Blue
"I have always wished that my computer would be as easy to use as my
telephone. My wish has come true. I no longer know how to use my
telephone."
- Bjarne Stroustrup (originator of C++) [quoted at the 2003
International Conference on Intelligent User Interfaces]
Click to expand...


Reginald Blue said:
Sharon said:
shuld i add new PrinterFactory class ?
Yes.

how do i implement it ?
Click to expand...

Depends on what you're trying to accomplish in the long term. Generally,
you'd have the factory look up the right thing to instantiate, but look up
from where is the main question. Perhaps just a case statement. But
maybe
you want something more dynamic, so you could have it load a new assembly
from disk.

So, generally, it's:

1. Receive request for creation of specific type.
2. Find specific type.
3. Create new instance of specific type.
4. Return new instance (via interface).
--
Reginald Blue
"I have always wished that my computer would be as easy to use as my
telephone. My wish has come true. I no longer know how to use my
telephone."
- Bjarne Stroustrup (originator of C++) [quoted at the 2003
International Conference on Intelligent User Interfaces]
Click to expand...
 
Thank you !


Reginald Blue said:
Sharon said:
so it will be somthing like :
Click to expand...
<code elided>

Yup, that's the factory pattern.

--
Reginald Blue
"I have always wished that my computer would be as easy to use as my
telephone. My wish has come true. I no longer know how to use my
telephone."
- Bjarne Stroustrup (originator of C++) [quoted at the 2003
International Conference on Intelligent User Interfaces]
Click to expand...
 
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