Simple Graphing Calculator with 2D array

Question

Hello,
I am building a simple graphing calculator which reads in coefficients from a txt file. All is going well except when I plot the points, the graph is at the corner of the screen and sideways. As we all know, the origin of the array is at the top right corner, so how do I transform/slide it so that it is at the xy origin? Code is posted below, thanks!
import javax.swing.*;
import java.awt.*;
public class baseClass extends JFrame{
     private shapesPanel panel;
     public baseClass(String title){
          panel = new shapesPanel();
          setTitle(title);
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          getContentPane().add(panel);
          pack();
          setVisible(true);
     public void drawLine(int x1, int y1, int x2, int y2){
          panel.addLine((short)x1,(short)y1,(short)x2,(short)y2);
          panel.repaint();
     public void drawDot(int x, int y){
          panel.addOval((short)x,(short)y,(short)1,(short)1);
          panel.repaint();
     private class shapesPanel extends JPanel{
          final private short max = 10000;
          private short[][] lines, ovals;
          private int numLines, numOvals;
          public shapesPanel(){
               setBackground(Color.white);
               setPreferredSize (new Dimension(500,500));
               lines = new short[max][4];
               ovals = new short[max][4];
               numLines = 0;
               numOvals = 0;
          public void paintComponent(Graphics g){
               super.paintComponent(g);
               g.setColor(new Color(0,0,255));
               for(int i = 0; i < numLines;++i){
                    g.drawLine(lines[0],lines[i][1],lines[i][2],lines[i][3]);
               g.setColor(new Color(255,0,0));
               for(int i = 0; i < numOvals;++i){
                    g.drawOval(ovals[i][0],ovals[i][1],ovals[i][2],ovals[i][3]);
          public void addLine(short x1, short y1, short x2, short y2){
               lines[numLines][0] = x1;
               lines[numLines][1] = y1;
               lines[numLines][2] = x2;
               lines[numLines][3] = y2;
               ++numLines;
          public void addOval(short x, short y, short w, short h){
               ovals[numOvals][0] = x;
               ovals[numOvals][1] = y;
               ovals[numOvals][2] = w;
               ovals[numOvals][3] = h;
               ++numOvals;
import java.util.Scanner;
import java.io.*;
public class graphingCalculator extends baseClass{
     // CONTAINS THE FOUR FUNCTION COEFFICIENTS
     private double[] theFunction;
// CONTAINS THE DISCRETE FUNCTION PLOT
private boolean[][] grid;
// SIZE OF THE COORDINATE SYSTEM
private final int columns = 500, rows = 500;
public graphingCalculator(String filename) throws IOException{
     // INITIALIZATIONS ///////////////////////////////////////
super("GRAPHING CALCULATOR");
theFunction = new double[4];
     grid = new boolean[rows][columns];
for(int i = 0;i<rows;++i){
for(int j = 0;j<columns;++j){
grid[i][j] = false;
// DRAW THE COORDINATE SYSTEM ON THE SCREEN /////////////
drawLine(0,250,500,250);
drawLine(250,0,250,500);
for(int i = 0; i < columns;i+=20){
drawLine(i,247,i,253);
for(int i = 0; i < rows;i+=20){
drawLine(247,i,253,i);
// GET THE FUNCTION COEFFICIENTS ///////////////////////
// theFunction[0] will have the x^3 coefficient
// theFunction[1] will have the x^2 coefficient
// theFunction[2] will have the x^1 coefficient
// theFunction[3] will have the x^0 coefficient
Scanner scan1 = new Scanner(new File(filename));
for(int i=0;i<4;++i){
     theFunction[i] = scan1.nextDouble();
scan1.close();
// DRAW THE FUNCTION ////////////////////////////////////
computeGrid();
drawDiscrete();
drawContinuous();
private double computeFunction(int x)
     double a=theFunction[0];
     double b=theFunction[1];
     double c=theFunction[2];
     double d=theFunction[3];
     double answer=(a*Math.pow(x,3.0)+b*Math.pow(x,2.0)+c*Math.pow(x,1.0)+d*Math.pow(x,0.0));
     return answer;
private void computeGrid()
          // Populate the 'grid' array with true values that correspond
          // to the discrete function.
          // The 'grid' array is the internal representation of the function
     for(int x=0; x<columns; x++)
               if(computeFunction(x)>=0&&computeFunction(x)<500)
               grid[(int)computeFunction(x)][x]=true;
private void drawDiscrete()
          // Use drawDot(x,y) to draw the discrete version of the function
     for(int x=0;x<columns;x++)
          for(int j=0;j<rows;j++)
     if(grid[x][j])
          drawDot(x,j);
private void drawContinuous()
          // Use drawLine(x1,y1,x2,y2) to draw the continuous version of the function

Answer 1

Rest of code:
import java.util.Scanner;
import java.io.*;
public class Main {
    public static void main(String[] args) throws IOException{
    String infile;
    Scanner scan = new Scanner(System.in);
    // The input file should have 4 doubles in it
    // corresponding to the 4 coefficients of a cubic function.
    // A GOOD EXAMPLE:
    //                  0.01
    //                  0.0
    //                  -5.0
    //                          50.0
    // CORRESPONDS TO FUNCTION: 0.01*X^3 - 5.0*X + 50.0       
    // ANOTHER GOOD EXAMPLE:
    //                  0.0
    //                  0.01
    //                  -1.0
    //                          -100.0
    // CORRESPONDS TO FUNCTION: 0.01*X^2 - X - 100.0       
    System.out.println("Please enter filename of input file: ");
    infile = scan.next();
    graphingCalculator cal = new graphingCalculator(infile);
}