I have written a very basic paint program in java using awt and swing. I have separated the program into two different class files; one of them holds the JFrame and adds a custom panel (this custom panel being the second class file, extending JPanel).

In my first try, I tried using Timer and an ActionListener with repaint() but that seemed very very laggy (I could not draw straight lines/curves, they would always be laggy when I dragged my mouse fast.)

Then I switched to using a different approach (stored previous x and y locations and drew a line between the current position and the previous location). Here are the two class files:

The custom JPanel class:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Panel extends JPanel
{
  // PROPERTIES
  private final int DEFAULT_WIDTH  = 800;
  private final int DEFAULT_HEIGHT = 800;
  private final Color BACK_COLOR   = Color.WHITE;
  
  private int x1, y1, x2, y2;
  
  private MyMouseHandler handler;
  private Graphics g;
  
  // CONSTRUCTOR
  public Panel()
  {
    setBackground( BACK_COLOR );
    setPreferredSize( new Dimension( DEFAULT_WIDTH, DEFAULT_HEIGHT ) );
    
    handler  = new MyMouseHandler();
    
    this.addMouseListener( handler );
    this.addMouseMotionListener( handler );
  }
  
  // METHOD
  public void paintComponent(Graphics g)
  {
    super.paintComponent(g);
  }
  
  private void setUpDrawingGraphics()
  {
    g = getGraphics();
  }
  
  // INNER CLASS
  private class MyMouseHandler extends MouseAdapter
  {
    public void mousePressed( MouseEvent e )
    {
      x1 = e.getX();
      y1 = e.getY();
      
      System.out.println("Mouse is being pressed at X: " + x1 + " Y: " + y1);
      
      setUpDrawingGraphics();
      
      x2=x1;
      y2=y1;
    }
    
    public void mouseDragged( MouseEvent e )
    {
      x1 = e.getX();
      y1 = e.getY();
      
      System.out.println("Mouse is being dragged at X: " + x1 + " Y: " + y1);  
      
      g.drawLine(x1,y1,x2,y2);
      
      x2=x1;
      y2=y1;
    }
  }
}

and the JFrame class with the main method:

import java.awt.*;
import javax.swing.*;

public class RunPanel
{
  public static void main(String[] args)
  {
    JFrame frame = new JFrame( "Run Panel" );
    frame.setDefaultCloseOperation(3);
    
    Panel  panel = new Panel();
    frame.add( panel );
    
    frame.pack();
    frame.setVisible( true );
  }
}

The program works fine, I can draw normal curves at low mouse speed. But again, as I increase the mouse speed the lines/curves start the get jaggy and ugly.

Maybe this is because I am drawing lines in between the positions, but drawing individual pixels look MUCH worse.

Any help would be appreciated :) Also please add your suggestions about anything you would like to point out.

NOTE: I have gathered the two classes into one class file and the program stoped the lag. What is causing this? You can see the code here.