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! ^___^

(Taken from bbr201's link)

--A few things to know--

Class variables are referenced by the class name itself, as in

Bicycle.numberOfBicycles

This makes it clear that they are class variables.


Note: You can also refer to static fields with an object reference like

 myBike.numberOfBicycles

but this is discouraged because it does not make it clear that they are class variables.


Class methods cannot access instance variables or instance methods directly—they must use an object reference. Also, class methods cannot use the this keyword as there is no instance for this to refer to.

Wow! Thanks a lot for the help, guys! That was quite enlightening!

So to be clear, the class variable can be used by all methods, but the instance variable can only be used by the method it is declared in, unless with object reference? Is that right?