MemorySaverCalc

import java.io.*;
import java.util.*;

import javax.swing.JFileChooser;

public class MemorySavingCalc {

    static boolean onStart = true;
    static CalcOpps calc = new CalcOpps();

    public static void main(String[] args) {

        if(onStart){
            CalcOpps.start();
            onStart = false;
        }
        double a = 0;
        System.out.println("Please chose an option.");
        int opt = CalcOpps.getMenuOption();
        if(opt > 0 && opt < 5){
            a = CalcOpps.getOperand("Please give the second operand.");

            if (opt == 1) {
                calc.add(a);
                System.out.println("The current value is: " + calc.getCurrentValue());
            }if (opt == 2) {
                calc.subtract(a);
                System.out.println("The current value is: " + calc.getCurrentValue());
            }if (opt == 3) {
                calc.multiply(a);
                System.out.println("The current value is: " + calc.getCurrentValue());
            }if (opt == 4) {
                calc.divide(a);
                System.out.println("The current value is: " + calc.getCurrentValue());
            }
        }
        if (opt == 5) {
            calc.clear();
            System.out.println("The current value is: " + calc.getCurrentValue());
        }if(opt == 6){
            calc.save();
        }
        if(opt == -1){
            opt = 0;
            main(null);
        }
        if(opt != 7){
            main(null);
        }
        if(opt == 7){
            System.out.println("Have a nice day.");
        }

    }

}
class CalcOpps{
    static Scanner in = new Scanner(System.in);
    private static double currentValue;
    private static ArrayList<String> list = new ArrayList<String>();
    JFileChooser saver = new JFileChooser();

    public static void start(){
        list.add("~~~~~~~start~~~~~~~" + "\r\n");
        System.out.println("Initial value is 0.0. Would you like to change this?\n1) Yes\n2) No");
        int opt = in.nextInt();
        if(opt == 1){
            System.out.println("Please enter a number.");
            currentValue = in.nextDouble();
            list.add("Starting value was changed to " + currentValue);
        }
        if(opt == 2){
            list.add("Starting value set to " + currentValue);
        }
        if(opt != 2 && opt != 1){
            System.out.println("Please choose a valid option.");
            start();
        }
    }

    public CalcOpps(){
        currentValue = 0.0;
    }

    public static int getMenuOption() throws InputMismatchException{
        int r;
        System.out.println("1) Addition\n2) Subtraction\n3) Multiplication\n4) Division\n5) clear\n6) Save\n7) Exit");
        try{
            r = -1;
            while(r < 0 ||r > 7){
                r = in.nextInt();
                if((r < 0 ||r > 7)){
                    System.out.println("Invalid Input.");
                }
            }
            return r;
        }catch(InputMismatchException e){
            System.out.println(e + ": Invalid Input");
        }
        return -1;
    }

    public static double getOperand(String prompt){
        System.out.println(prompt);
        double r = in.nextDouble();
        return r;
    }

    public void add(double a){
        list.add(currentValue + " + " + a + " = " + (currentValue + a) + "\r\n");
        currentValue += a;
    }

    public void subtract(double a){
        list.add(currentValue + " - " + a + " = " + (currentValue - a) + "\r\n");
        currentValue -= a;
    }

    public void multiply(double a){
        list.add(currentValue + " * " + a + " = " + (currentValue * a) + "\r\n");
        currentValue = currentValue * a;
    }

    public void divide(double a){
        if(a == 0){
            System.out.println("Cannot divide by 0. Please clear, and try again.");
            currentValue = Double.NaN;
        }
        list.add(currentValue + " / " + a + " = " + (currentValue / a) + "\r\n");
        currentValue = currentValue / a;
    }

    public double getCurrentValue(){
        return currentValue;
    }

    public void clear(){
        currentValue = 0.0;
    }
    public void save(){
        list.add("~~~~~~~~end~~~~~~~~");
        saver.setCurrentDirectory(new File("C:/Users/gdog2_000/Desktop"));
        int test = saver.showSaveDialog(null);
        if(test == JFileChooser.APPROVE_OPTION){
            try(FileWriter fw = new FileWriter(saver.getSelectedFile() + ".txt")){
                for(int i = 0; i < list.size(); i++){
                    fw.write(list.get(i));
                }
            fw.close();
            }catch(IOException ex){

            }
        }
    }
}