java.util.IllegalFormatConversionException: f != java.lang.String Error

Question

import javax.swing.JOptionPane;

public class Minutes {

    public static void main(String[] args) {
        double  BasePlanCost = 20;
        final double BaseCos         


        

Answer 1

Try to organize your message as:

String message = String.format(
            "**IST Wireless Receipt** \n" + 
            " Base Plan Cost:$ %.2f \n" +
            " Cost For Minutes Used: $ %.2f \n" +
            " Grand Total : $ %.2f", BasePlanCost, CostForMinutes, GrandTotal);

    JOptionPane.showMessageDialog(null, message);

I recommended you to read the code conventions of the java language

http://www.oracle.com/technetwork/java/codeconventions-135099.html

Answer 2

You have

String.format("$%.2f","**IST Wireless Receipt**",

This means you want to format the second argument which is a String using %.2f which is a float format which won't work.

You need to re-organize your format to be first and the values you want to format after it.

String.format("**IST Wireless Receipt**%n" +
              "Base Plan Cost: $%.2f%n" +
              "Cost For Minutes Used: $%.2f%n" +
              "Grand Total: $%.2f%n",
              BasePlanCost, CostForMinutes, GrandTotal)