Need to add the numbers from an object

Question

I am writing a program that takes names, dates and numbers from a user as many times as they enter it and then adds up the numbers that were entered. If you look at the third for loop you will see where I am trying to add. I tried doing total = cust[i].amount + total; but I cannot access amount for some reason.

This is for an assignment.(I know were not supposed to post homework questions on here but I'm stumped.)The only data member Customer is to have is name

public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        final int MAX = 9999;
        Customer [] cust = new Customer[MAX];
        int choice = 0;
        int cnt;

        double total = 0;

        for(cnt=0; cnt < MAX && (choice == 1 || choice ==2 || choice == 0); cnt++){
            System.out.println("For a Service customer type 1, for a Purchaser type 2, to terminate the program press 9");
            choice = s.nextInt();
            switch (choice){
            case 1:
                cust [cnt] = new Service();
                break;
            case 2:
                cust [cnt] = new Purchaser();
                break;
            default:
                break;
            }
        }
        for(int i=0; i < cnt; i++){
            if(cust[i]!= null)
            cust[i].showData();
        }
        for(int i=0; i < cnt; i++ ){
            total = cust[i].amount + total;
        }
            s.close();

    }
}
interface Functions {
    public void getData();
    public void showData();
}
abstract class Customer implements Functions {
    protected String name;


}
class Purchaser extends Customer {
    protected double payment;

    public Purchaser(){
        getData();
    }

    public void getData() {
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the name of the customer");
        name = s.nextLine();
        System.out.println("Enter payment amount: ");
        payment = s.nextDouble();
    }
    public void showData() {    
        System.out.printf("Customer name: %s Payment amount is: %.2f\n",name,payment);

    }   
}
class Service extends Customer {
    protected String date;
    protected double amount;
    public Service () {
        getData();

    }

    public void getData() {     
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the name of the customer");
        name = s.nextLine();
        System.out.println("Enter date of Service: ");
        date = s.nextLine();
        System.out.println("Enter the cost of Service: ");
        amount = s.nextDouble();
    }
    public void showData() {
        System.out.printf("Customer name: %s The date is: %s, the Amount owed is: %.2f\n",name, date, amount);
    }

possible duplicate of [Why am I getting an error!?(Null pointer Exception)](http://stackoverflow.com/questions/21446262/why-am-i-getting-an-errornull-pointer-exception) — Elliott Frisch, Jan 30 '14 at 02:51
Unrelated, but there's a subtle bug in the `for` loop. It needs to be `for(cnt=0; cnt < MAX && ( choice == 1 || choice ==2 || choice == 0); cnt++)` because `&&` has higher precedence than `||`. — Dawood ibn Kareem, Jan 30 '14 at 02:53
Is all your code in the same package? Or are there different packages here? — Dawood ibn Kareem, Jan 30 '14 at 02:56
What does the code your are having trouble with even do? I ran your program without it, and it seemed fine, at least with the code you provide — BlackHatSamurai, Jan 30 '14 at 03:55

score 4 · Answer 1 · answered Jan 30 '14 at 02:56

4

There's no field amount in the class Customer.

answered Jan 30 '14 at 02:56

user3173787

87
7

1

+1. I would just add that maybe the OP forgot that `amount` is in the `Service` class which extends `Customer`. The OP might want to learn about inheritance. – Nico Jan 30 '14 at 03:00
I realize that it is in the service class. Is there anyway to access it with the cust[i] object? – user278153 Jan 30 '14 at 03:03
2

If you don't want to change the inheritance structure, just add a method getAmount() in your interface. The downside is that you'll be forced to implement this method in Purchase as well. – user3173787 Jan 30 '14 at 03:06
Implementing the method in the Purchase would be a good idea since the data coming in is the same representation – BlackHatSamurai Jan 30 '14 at 05:07

Elliott Frisch · Answer 2 · 2014-01-30T03:37:43.377

There are several issues, but you should

// Use one loop...
for(int i=0; i < cnt; i++){
  if(cust[i]!= null) { // <-- check for null.
    cust[i].showData();
    /* or
    if (cust instanceof Service) {
      total += ((Service)cust[i]).amount; // <-- assuming a public amount 
                                   // field in Service. This is not a good
                                   // practice, but your question is difficult to 
                                   // answer.
    }
    */
    total += cust[i].getAmount(); // <-- a method.
  }
}

That is add a getAmount to your interface if you want to get the amount (or, to make this code work - change the access modifier and add a public field named amount to Customer and remove the shadowing fields in your subclasses).

Or, you can learn about Collections (which I strongly recommend you do anyway) - and actually use the correct storage method - perhaps ArrayList.

tried making it public, that did not work. I'll try the getter — user278153, Jan 30 '14 at 03:00
@user278153 There's another issue then. I suggest looking into how you declare the amount variable. — Steve, Jan 30 '14 at 03:01

BlackHatSamurai · Accepted Answer · 2014-01-30T04:50:58.963

1

This is one solution that I could come up with, where we add a getAmount method to the interface:

import java.util.Scanner;


public class home {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        final int MAX = 2;
        Customer [] cust = new Customer[MAX];
        int choice = 0;
        int cnt;

        double total = 0;

        for(cnt=0; cnt < MAX && (choice == 1 || choice ==2 || choice == 0); cnt++){
            System.out.println("For a Service customer type 1, for a Purchaser type 2, to terminate the program press 9");
            choice = s.nextInt();
            switch (choice){
            case 1:
                cust [cnt] = new Service();
                break;
            case 2:
                cust [cnt] = new Purchaser();
                break;
            default:
                break;
            }
        }
        for(int i=0; i < cnt; i++){
           if(cust[i]!= null)
           cust[i].showData();
           total = cust[i].getAmount() + total;
        }
            s.close();

    }
}

abstract class Customer implements Functions {
    protected String name;


}

import java.util.Scanner;


class Service extends Customer {
    protected String date;
    protected double amount;
    public Service () {
        getData();

    }

    public void getData() {     
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the name of the customer");
        name = s.nextLine();
        System.out.println("Enter date of Service: ");
        date = s.nextLine();
        System.out.println("Enter the cost of Service: ");
        amount = s.nextDouble();
    }
    public double getAmount(){
        return this.amount; 
    }
    public void showData() {
        System.out.printf("Customer name: %s The date is: %s, the Amount owed is: %.2f\n",name, date, amount);
    }

}


    import java.util.Scanner;

class Purchaser extends Customer {
    protected double payment;

    public Purchaser(){
        getData();
    }

    public double getAmount(){
        return this.payment; 
    }
    public void getData() {
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the name of the customer");
        name = s.nextLine();
        System.out.println("Enter payment amount: ");
        payment = s.nextDouble();
    }
    public void showData() {    
        System.out.printf("Customer name: %s Payment amount is: %.2f\n",name,payment);

    }   
}



interface Functions {
    public void getData();
    public void showData();
    public double getAmount();
}

edited Jan 30 '14 at 04:50

answered Jan 30 '14 at 02:53

BlackHatSamurai

23,275
22
95
156

@DavidWallace good point, I changed it. Been working with PHP too much lately... Lol – BlackHatSamurai Jan 30 '14 at 02:56
Also needs a change in the `Service` class to make this work. – Dawood ibn Kareem Jan 30 '14 at 03:00
this is for an assignment.(I know were not supposed to post homework questions on here but I'm stumped.)The only data member Customer is to have is name. – user278153 Jan 30 '14 at 03:02
1

You should probably add that restriction to the question, otherwise more people will give you answers that involve adding `amount` as a field (data member). – Dawood ibn Kareem Jan 30 '14 at 03:03
@DavidWallace good point. I'm surprised you didn't post the answer yourself :) – BlackHatSamurai Jan 30 '14 at 03:03
@user278153 I just posted a new answer for you that should work. It adds another method to your interface that allows you to access the amount and payment for both. Be aware that I broke my code up into different files which is why it has multiple imports. – BlackHatSamurai Jan 30 '14 at 04:04
doesn't let me use the getAmount method. It says return type is incompatible. – user278153 Jan 30 '14 at 04:17
@user278153 Check your code. Make sure everything is set to double, including the implementation in the interface. The code worked for me. You probably don't have something set to double. – BlackHatSamurai Jan 30 '14 at 04:44
@user278153 Happy to hear it is working now. Feel free to upvote as well :) – BlackHatSamurai Jan 30 '14 at 04:56
Unfortunately I can't up vote, haven't hit 15 rep yet. – user278153 Jan 30 '14 at 05:00
1

@user278153 you can now :) – BlackHatSamurai Jan 30 '14 at 05:06
The getAmounts() method accesses both the Purchaser class and the Service class. I only want the Service class amoounts to be added. Is there a way to only call the method from the service class? – user278153 Jan 30 '14 at 13:46
@user278153 Yes, but that would be another question my friend. I'm sure you can figure it out. I will add that you would have to redo a lot of what you have done. :) – BlackHatSamurai Jan 30 '14 at 19:21

Need to add the numbers from an object

3 Answers3