Thread: Basic program which gets cost, adds tax, gets payment then calculates change.

Here is the code:

import java.io.*;
 
class Change
{
	double cost;
	double tax;
	double payment;
 
	public void setCost(double x)
	{
		cost = x;
	}
	public double getCost()
	{
		return cost;
	}
	public void setTax(double x)
	{
		tax = x;
	}
	public double getTax()
	{
		return (cost+tax);
	}
	public void setPayment(double x)
	{
		payment = x;
	}
	public double getPayment()
	{
		return (payment-tax);
	}
	public static void main (String [] args) throws Exception
	{
		BufferedReader object = new BufferedReader (new InputStreamReader (System.in));
 
		Change change = new Change();
 
		System.out.println("Welcome to the Supermarket!");
		System.out.println("");
		System.out.println("How much is the total cost?");
		System.out.println("Input here: ");
		cost = Double.parseDouble (object.readLine());
 
		change.setCost(cost);
		System.out.println("");
		System.out.println("The cost is: "+change.getCost());
		System.out.println("");
 
		tax = cost * 0.06;
		System.out.println("");
		System.out.println("The tax is: "+tax);
		change.setTax(tax);
		System.out.println("The total cost is: "+change.getTax());
		System.out.println("");
 
		System.out.println("How much will you pay?");
		System.out.print("Input here:");
		payment = Double.parseDouble(object.readLine());
		System.out.println("");
 
		change.setPayment(payment);
		System.out.println("Your change is "+change.getPayment());
		System.out.println("");
		System.out.println("Have a nice day!");
	}
}

But it has 8 errors of the same origin:

 
Main.java:43: non-static variable cost cannot be referenced from a static context
		cost = Double.parseDouble (object.readLine());
		^
Main.java:44: non-static variable cost cannot be referenced from a static context
		change.setCost(cost);
		               ^
Main.java:48: non-static variable tax cannot be referenced from a static context
		tax = cost * 0.06;
		^
Main.java:48: non-static variable cost cannot be referenced from a static context
		tax = cost * 0.06;
		      ^
Main.java:50: non-static variable tax cannot be referenced from a static context
		System.out.println("The tax is: "+tax);
		                                  ^
Main.java:51: non-static variable tax cannot be referenced from a static context
		change.setTax(tax);
		              ^
Main.java:56: non-static variable payment cannot be referenced from a static context
		payment = Double.parseDouble(object.readLine());
		^
Main.java:58: non-static variable payment cannot be referenced from a static context
		change.setPayment(payment);
		                  ^
8 errors

What do those errors mean? Can someone please explain and/or correct them? Thank you so much! ^___^