can I hide variables on a inheritance hierarchy in java?

Question

I am trying to create a program where there is a method with a formula.This formula is exported to other classes, but each class uses different variables.

when I use my program the mothods and variables are exported and I only want to export the method (formula) from Bronce class to Silver class.

If I cannot hide variables, how canI overcome this problem??

I am new at java

Bronze Class

public  class Bronze  {

    // ----------------- Atributes -----------------------

    private static final double costDay = 0.12;

    public int dayMinutes;      // daytime telphone minutes used

    public double dayTimeCost;  //Total daytime calls cost

    // ------------- CONSTRUCTORS (inputs) ---------------

    public Bronze(int theDayMinutes ) {  
    dayMinutes = theDayMinutes; 
    }
    // ------------------ METHODS ------------------------
    // Calculate Total daytime calls cost
    public double calcDayTimeCost() {

        dayTimeCost = dayMinutes * costDay;
        return dayTimeCost;
    }

    //toString method to override that in Object
    public String toString(){
    return("\nCost of daytime calls = " + costDay + "/min"+
        "\n\nTotal daytime calls cost = " + dayTimeCost + 
 "\n" 
         );
    }

    //Returns the type of account
    public String type(){
    return "Bronze";
    }
}

Silver Class

public class Silver extends Bronze {

    private static final double costDay = 0.22;

    public Silver(int theDayMinutes ) {
    super(theDayMinutes );

  }
    //Returns the type of account
    public String type(){
    return "Silver";
    }

}

Main Class

import java.util.Scanner;

public class AccountUser {

    // ------------------- FIELDS ------------------------    

    // Create instance of Scanner class
    public static Scanner input = new Scanner(System.in);
    // variables
    public static Bronze bron;
    public static Silver silv;

    public static int dayMinutes;

    // ------------------ METHODS ------------------------  

    public static void main(String [] args) {

        // Input dayMinutes (with error message)
        do{
        System.out.print("Please daytime telphone minutes used --> ");
        dayMinutes  = input.nextInt();
        if  ( dayMinutes <= 0){System.out.print("\n" + "Input value outside the range!!!" + "\n");}
        }while( dayMinutes <= 0);


        // Create new Bronze instance
        bron = new Bronze(dayMinutes);
        silv = new Silver(dayMinutes);
        // Calculate scheme1, scheme2
        bron.calcDayTimeCost();
        silv.calcDayTimeCost();


    System.out.println(bron);
    System.out.println(silv);
    }
}

Answer 1

Make costDay a parameter to the method. public double calcDayTimeCost(double costDay) then call it with silv.calcDayTimeCost(0.22)

Answer 2

While the keyword overriding is wrong here because it does not apply for class fields, the concept of shadowing still applies.

Right now when you invoke calcDayTimeCost on your Silver object it uses the super field of costDay .

You have to change it to

 protected double costDay = 0.12; // Bronze class

and

 public Silver(int theDayMinutes ) {
    super(theDayMinutes );
    super.costDay = 0.12;
  }