Help needed on homework assignment!!!

Question

I am new to Java. Could anybody please help me figure out the problem in my code. I have to
The class A2 has to perform this operation:
It will prompt for user�s inputs, call the methods of the other two classes to convert the date and calculate the stock sale, and displays the outputs on the screen.
The class SellStocks has to perform this operation:
It will provide instance methods with parameters to calculate the value of the shares, the commission and the net proceeds of a stock.
The A2 class code is:
import jpb.*;
public class A2 {
  public static void main(String[] args) {
    SimpleIO.prompt("Enter today's date: ");
    String date = SimpleIO.readLine();
    SimpleIO.prompt("Enter stock price: ");
    String price = SimpleIO.readLine();
    SimpleIO.prompt("Enter number of shares: ");
    String number = SimpleIO.readLine();
    SimpleIO.prompt("Enter commission rate (as a percentage) : ");
    String rate = SimpleIO.readLine();
    double number1 = Convert.toDouble(number);
    double price1 = Convert.toDouble(price);
    double rate1 = Convert.toDouble(rate);
    SellStocks stock = new SellStocks();
    stock.sell(number1, price1, rate1);
    System.out.println();
    System.out.println("Today is: " + date);
    System.out.println("Value of shares: $" + price);
    System.out.println("Commission: $" + number);
    System.out.println("Net Proceeds: $" + rate);
}And the SellStocks class is:
public class SellStocks {
    private double value;
    private double commission;
    private double proceeds;
    public void sell (double num, double pri, double rat) {
     value = pri * num;
     commission = value * rat;
     proceeds = value - commission;
     pri = value;
     num = commission;
     rat = proceeds;
}I would really appreciate it if anybody could help me. Thanks a lot

Answer 1

Java is purely pass-by-value. The consequence of this is that when you change the value of a parameter inside a method, that change is not reflected in the caller.
If you need that method to modify three values and have all three changes seen by the caller then you can do it one of two ways. Either way, you need an object that encapsulate those three values.
In one solution, you pass a reference to that object to the method, and the method simply modifies that object's fields in place. (QUIZ: This may seem to be contradictory with the bolded statement above. (Does it?) It's not. Why?)
The other way is to have the method create that object and simply return a reference to it. In your case here, either one will work fine, but I'd lean toward the second one as a better division of responsibility.