How to use Polymorphism

[nfsmwbe]

CyberCafe.java

public abstract class CyberCafe{
	String cust_name;
	int pc_no;
	
	public CyberCafe(String cn, int pn){
		cust_name = cn;
		pc_no = pn;
	}
	
	public String getCustName(){
		return cust_name;
	}
	
	public int getPC(){
		return pc_no;
	}
	
	public abstract double calcTotCharge();
}

Printing.java

public class Printing extends CyberCafe{
	int no_of_print;
	boolean colour;
	
	public Printing(String cn, int pn, int p, boolean c){
		super(cn, pn);
		no_of_print = p;
		colour = c;
	}
	
	public int getNoOfPrint(){
		return no_of_print;
	}
	
	public boolean getColour(){
		return colour;
	}
	
	public double calcTotCharge(){
		double charge;
		if(colour){
			charge =  0.7 * no_of_print;
		}
		else{
			charge =  0.3 * no_of_print;
		}
		return charge;
	}
}

Internet.java

public class Internet extends CyberCafe{
	String start_time;
	String end_time;
	int no_of_files_downloaded;
	
	public Internet(String cn, int pn, String s, String e, int d){
		super(cn, pn);
		start_time = s;
		end_time = e;
		no_of_files_downloaded = d;
	}
	
	public String getStartTime(){
		return start_time;
	}
	
	public String getendTime(){
		return end_time;
	}
	
	public int getDownloadedFiles(){
		return no_of_files_downloaded;
	}
	
	public double calcTotCharge(){
		double charge = 0.0;
		int min = 0;
		
		int startH = Integer.parseInt(start_time.substring(0, 2));
		int startM = Integer.parseInt(start_time.substring(2));
		int endH = Integer.parseInt(end_time.substring(0, 2));
		int endM = Integer.parseInt(end_time.substring(2));
		
		//calculate minutes
		if(startH == endH){
			min = endM - startM;
		}
		
		else if(startH < endH){
			min = ((endH - startH -1) * 60) + endM + (60 - startM);
		}

		else{
			min = (((24 - startH) + endH - 1) * 60) + endM + (60 - startM);
		}
		
		//calculate charge
		if(min < 120){
			charge = 2.5;
		}
		
		else{
			charge = 2.5 + ((((min - 120) / 30) + 1) * 0.5);
		}
		
		//calculate total charges
		charge = charge + (1.5 * no_of_files_downloaded);
		return charge;
	}
}

myCyberCafeAPP.java

import java.util.Scanner;
public class myCyberCafeAPP{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter no of customer: ");
		int cust = input.nextInt();
		
		CyberCafe[] myCafePrint= new CyberCafe[cust];
		CyberCafe[] myCafeInternet= new CyberCafe[cust];
		System.out.print("\n");
		
		for(int i=0; i<cust; i++){
			System.out.print("Customer Name: ");
			String name = input.next();
			System.out.print("Phone No: ");
			int phone = input.nextInt();
			
			System.out.print("No of Print: ");
			int print = input.nextInt();
			System.out.print("Colour (Yes/No): ");
			String colour = input.next();
			boolean c;
			if(colour.equalsIgnoreCase("Yes")){
				c = true;
			}
			else{
				c = false;
			}
			
			System.out.print("Start Time (eg: 1420): ");
			String start = input.next();
			System.out.print("End Time (eg: 1430): ");
			String end = input.next();
			System.out.print("No of Files Downloaded: ");
			int download = input.nextInt();
			
			myCafePrint[i] = new Printing(name, phone, print, c);
			myCafeInternet[i] = new Internet(name, phone, start, end, download);
		}
		
		double total = 0.0;
		for(int j=0; j<cust; j++){
			total = total + myCafePrint[j].calcTotCharge() + myCafeInternet[j].calcTotCharge();
		}
		System.out.print("Total Charge: RM " + total);
	}
}

is this true?
should i declare 2 array object (line 8 & 9 in myCyberCafeAPP.java)..
help me..i don't really understand polymorphism...

[JosAH]

Polymorphism is calling the same method (i.e. same name, same number of parameters, same types) on two different objects. The implementation of the method in the two different objects can differ of course. If two different classes implement one interface, the methods from the interface can be called polymorphically. If one class extends another class and overrides a method, the implementations of the methods in the sub class and the super class can also be called polymorphically.

kind regards,

Jos

[nfsmwbe]

in this case, what should i do..
can i declare only 1 array object to get total charge..

[JosAH]

in this case, what should i do..
can i declare only 1 array object to get total charge..

I really don't know what arrays have to do with polymorphism; care to explain what you have in mind?

kind regards,

Jos

[Tolls]

I htink this has little to do with polymorphism as such.
Your inheritance model (ie X is-a Y) is suspect.
Printing is-a CyberCafe?
Internet is-a CyberCafe?

[nfsmwbe]

i mean the right and simplest way to get total charge
using concept of inheritance n polymorphism..
just give me hint..i'm new in java..
thanks in advance...

[Tolls]

Have an interface, ChargeableItem, with a single method, "double calcTotCharge();".
Have all things that are Chargeable implement that interface.
Stick those in a List<ChargeableItem> for whoever is using the CyberCafe.
When you want to total up the cost to the client loop round the List calling calcTotCharge() (though I would probably call it getCharge()).

[nfsmwbe]

thanks..
i'll try..

[nfsmwbe]

Stick those in a List<ChargeableItem> for whoever is using the CyberCafe.

what does it mean..
can u give an example...
i don't know how to start...

[Tolls]

OK.
SOmeone goes into your CYberCafe and buys some things (time on the internet, some printing, and a coffee)...these (as far as I can make out in what you;re doing) get associated with that person. That's your List of ChargeableItems.

[nfsmwbe]

sorry, i don't get it..
i already read a lot about interface but i don't understand how to apply in this situation...
can you explain in simple code...
what difference between "double calcTotCharge();" and "ChargeableItem" ?