What is wrong with this code

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package javaclass;

import java.awt.BorderLayout;
import java.awt.Point;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class PaintPanel extends JPanel {

private int pointCount = 0; // count number of points
// array of 10000 java.awt.Point references
private Point points[] = new Point[10000];

// set up GUI and register mouse event handler
public PaintPanel() { // اینجا معلوم نیست چه ورودی داره

// handle frame mouse motion event
addMouseMotionListener(
new MouseMotionAdapter() { // anonymous inner class {
// store drag coordinates and repaint
public void mouseDragged(MouseEvent event) {
if (pointCount < points.length) {
points[ pointCount] = event.getPoint(); // find point
pointCount++; // increment number of points in array
repaint(); // repaint JFrame
} // end if
} // end method mouseDragged
} // end anonymous inner class
); // end call to addMouseMotionListener
} // end PaintPanel constructor

// draw oval in a 4-by-4 bounding box at specified location on window
public void paintComponent(Graphics g) { // اینجا هم میگه تعریف شده نیست
super.paintComponent(g); // clears drawing area
// draw all points in array
for (int i = 0; i < pointCount; i++) {
g.fillOval(points[ i].x, points[ i].y, 20, 20);
}
} // end method paintComponent

public static void main(String args[]) {
// create JFrame
JFrame application = new JFrame("A simple paint program");
PaintPanel paintPanel = new PaintPanel(); // create paint panel
application.add(paintPanel, BorderLayout.CENTER); // in center
// create a label and place it in SOUTH of BorderLayout
application.add(new JLabel("Drag the mouse to draw"),
BorderLayout.SOUTH);
application.setDefaultCloseOperation(JFrame.EXIT_O N_CLOSE);
application.setSize(400, 200); // set frame size
application.setVisible(true); // display frame
} // end main
} // end class PaintPanel