为什么我的程序返回“0.0”？

Question

I have created a business program that takes in double values with a loop and calculates net profit. I am required to add the input values from the main class to a custom class called Business. Then I am supposed to calculate the net Profit in the Business class and print the final value to the main class. When I run my current program, the result is "0.0". The Business class is not getting my input values from my main class, but I can't figure out why. Main class below:

public class BusinessProject {

public static double revenue;
public static double expenses;
public static double TotalRevenue;
public static double TotalExpenses;

public static void main(String[] args) {

    Business calc = new Business();

    getTotalRevenue();
    getExpense();
    calc.Profit();

}   
public static double getTotalRevenue() {    
    Scanner scan = new Scanner(System.in);

    while (true) {
        System.out.println("Enter your revenue: \nJust type 0 when you've finished inputting all values");
        revenue = scan.nextDouble();
        TotalRevenue += revenue;


    if(revenue==0) {

        break;
    }
}
    return TotalRevenue;
}
public static double getExpense() { 

    Scanner scan = new Scanner(System.in);

    while (true) {
        System.out.println("Enter your expenses: \nJust type 0 when you've finished inputting all values");
        expenses = scan.nextDouble();
        TotalExpenses += expenses;

    if(expenses==0) {

        break;

        }
    }
    return TotalExpenses;
}
}

Second Custom Class:

public class Business {

public static double ExpenseInput;
public static double RevenueInput;

public void REVENUE() {

    BusinessProject TOTAL = new BusinessProject();

    double RevenueInput = BusinessProject.TotalRevenue;

}

public static void EXPENSE() {

    BusinessProject TOTAL2 = new BusinessProject();

    double ExpenseInput = BusinessProject.TotalExpenses;
}

public void Profit() {

    double difference = (RevenueInput - ExpenseInput);

    if (difference <=1000) {

        System.out.println("Net Profit: " + (difference - (difference * 0.00175)));
    }

}

}

Answer 1

You get 0.0 because you haven't called your methods to set RevenueInput and ExpenseInput.

So in your case calling EXPENSE() and REVENUE() before profit() would solve it.

However, I'd advice you to look over your program structure and naming convention. You could either pass the variables as arguments for your function such as: Profit(double expense, double revenue) or you could have it in the constructor of Business like so: public Business(double expense, double revenue)

What you have right now is a circular dependency where you are relying on static variables in the class(BusinessProject) that your object(Business) then uses.

I would personally refactor it like this:

public class Business {
    public static void profit(final double revenue, final double expense) {
        double difference = (revenue - expense);

        if (difference <=1000) {

            System.out.println("Net Profit: " + (difference - (difference * 0.00175)));
        }

Then from your main project you simply call Business.profit(TotalRevenue, TotalExpense);

Answer 2

Instead of passing Business object you are creating new Business object in main class. Hence properties will be initialized with default values

You have to call EXPENSE() and Profit() from main class and you have to pass Business class as parameter to those methods

Answer 3

public void Profit(BusinessProject bp) {

    double difference = (bp.TotalRevenue - bp.TotalExpenses);

    if (difference <=1000) {

        System.out.println("Net Profit: " + (difference - (difference * 0.00175)));
    }

}

and call it as below

calc.Profit(this);