import java.awt.*;
import java.applet.*;

public class Quadra extends Applet {
  drawQuadra drawingCanvas;
  Panel PrmPanel;
  TextField TFprmA, TFprmB, TFprmC;
  double prmA=0.5, prmB=2.0, prmC=-3.0;

  public void init() {
    setLayout(new BorderLayout());

    PrmPanel = new Panel();
    PrmPanel.setLayout(new FlowLayout());
    PrmPanel.add(new Label("Y=", Label.RIGHT));
    PrmPanel.add(TFprmA = new TextField(String.valueOf(prmA), 4));
    PrmPanel.add(new Label("X^2 + "));
    PrmPanel.add(TFprmB = new TextField(String.valueOf(prmB), 4));
    PrmPanel.add(new Label("X + "));
    PrmPanel.add(TFprmC = new TextField(String.valueOf(prmC), 4));

    add("Center", drawingCanvas = new drawQuadra(prmA, prmB, prmC));
    add("South",  PrmPanel);
  }

  public boolean action(Event ev, Object arg) {
    if (ev.target instanceof TextField) {
      prmA = Float.valueOf(TFprmA.getText().trim()).floatValue();
      prmB = Float.valueOf(TFprmB.getText().trim()).floatValue();
      prmC = Float.valueOf(TFprmC.getText().trim()).floatValue();
      drawingCanvas.redraw(prmA, prmB, prmC);
      return true;
    } else
      return true;
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      stop();
      destroy();
      System.exit(0);
      return true;
    } else {
      return super.handleEvent(e);
    }
  }

  public static void main(String args[]) {
    PFrame f = new PFrame("Quadratic Function");
    Quadra quadratic_function = new Quadra();

    quadratic_function.init();
    quadratic_function.start();

    f.add("Center", quadratic_function);
    f.resize(420, 500);
    f.show();
  }
}

class PFrame extends Frame {
  PFrame(String title) {
    super(title);
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      dispose();
      System.exit(0);
    }
    return false;
  }
}
    
class drawQuadra extends Canvas {
  double paramA = 0.1, paramB = -0.0, paramC = -3.0;
  Point A = new Point(0,0), B = new Point(0,0);
  Point O = new Point(0,0);
  Point U = new Point(20,20);
  int Height, Width;

  drawQuadra(double paramA, double paramB, double paramC) {
    this.paramA = paramA;
    this.paramB = paramB;
    this.paramC = paramC;
    repaint();
  }

  public void redraw(double paramA, double paramB, double paramC) {
    this.paramA = paramA;
    this.paramB = paramB;
    this.paramC = paramC;
    repaint();
  }

  public void aw2px(Point t, double x, double y){
    t.x = (int)(   x * (double)U.x + (double)O.x );
    t.y = (int)( - y * (double)U.y + (double)O.y );
  }

  public void draw_coordinate(Graphics g) {
    Height = size().height;
    Width  = size().width;
    O.x = Height / 2;
    O.y = Width  / 2;

    g.setColor(Color.pink);
    for (int i = -10; i <= 10; i++) {
      aw2px(A, -10,i);  aw2px(B,  10,i);
      g.drawLine(A.x, A.y, B.x, B.y);
    }
    for (int i = -10; i <= 10; i++) {
      aw2px(A, i,-10);  aw2px(B, i, 10);
      g.drawLine(A.x, A.y, B.x, B.y);
    }

    g.setColor(Color.black);
    aw2px(A,0,-10); aw2px(B,0, 10);
    g.drawLine(A.x, A.y, B.x, B.y);
    aw2px(A,-10,0); aw2px(B,10,0);
    g.drawLine(A.x, A.y, B.x, B.y);
  }

  public void paint(Graphics g) {
    draw_coordinate(g);
    g.setColor(Color.red);

    double ss = -10.0, sss;
    while( ss < 10.0 ){
      sss = ss + 0.01;
      aw2px(A, ss, paramA * ss * ss + paramB * ss + paramC);
      aw2px(B, sss,paramA * sss * sss + paramB * sss + paramC);
      g.drawLine(A.x, A.y, B.x, B.y);
      ss = sss;
    }
  }

}