title: java 2D drawing
body: <p>im trying to make a swing app that draws a function's graph(simple for now ex. x+2)
  but i'm having problems to make  mathematical coordinates of my points depending on screen coordinates . 
  I want it to simply draw a line that goes from P1(0,1) to P2(1,2) inside my graph.</p>
  
  <p>here is  my code : </p>
  
  <pre><code>import java.awt.*;
  import javax.swing.*;  
  public class Graph extends JPanel {
  
     protected void paintComponent(Graphics g) {
       int YP1,YP2;
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D)g;
  
        int h = getHeight();
           int w = getWidth();
           // Draw axeX.
           g2.draw(new Line2D.Double(0, h/2, w, h/2)); //to make axisX in the middle
           // Draw axeY.
           g2.draw(new Line2D.Double(w/2,h,w/2,0));//to make axisY in the middle of the panel
  
                    //line between P1(0,1) and P2(1,2) to draw function x+1
      Point2D P1 = new Point2D.Double(w/2,(h/2)+1);
      Point2D P2 = new Point2D.Double((w/2)+1,(h/2)+2);
       g2.draw(new Line2D.Double(P1,P2));
  }
  public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new Graphe());
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
  }
  </code></pre>
  
  <p>thanks.</p>