Exception inspite of successful build

Question

i am running the following code it shows no exception if i dont click inside the applet
but if i click it shows the following exception.
what could be the possible reason for that
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: component argument pData
        at sun.awt.windows.Win32SurfaceData.initOps(Native Method)
        at sun.awt.windows.Win32SurfaceData.<init>(Win32SurfaceData.java:448)
        at sun.awt.windows.Win32SurfaceData.createData(Win32SurfaceData.java:316)
        at sun.awt.Win32GraphicsConfig.createSurfaceData(Win32GraphicsConfig.java:357)
        at sun.awt.windows.WComponentPeer.replaceSurfaceData(WComponentPeer.java:332)
        at sun.awt.windows.WComponentPeer.replaceSurfaceData(WComponentPeer.java:313)
        at sun.awt.windows.WComponentPeer$2.run(WComponentPeer.java:353)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)
BUILD SUCCESSFUL (total time: 4 seconds)My code is as follows
import java.awt.BorderLayout;
import javax.swing.JApplet;
* @author sakshi
public class MainJA extends JApplet {
    MyInterface in;
    MyJPanel jp1;
    MyJScrollPane jsp;
     * Initialization method that will be called after the applet is loaded
     * into the browser.
    @Override
    public void init() {
        makeGUI();
    // TODO start asynchronous download of heavy resources
    void makeGUI() {
        setLayout(new BorderLayout());
        jp1 = new MyJPanel();
        in = new MyInterface();
        jsp = new MyJScrollPane(jp1);
        add(jsp, BorderLayout.CENTER);
        add(in, BorderLayout.SOUTH);
    // TODO overwrite start(), stop() and destroy() methods
import java.awt.FlowLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
* @author sakshi
public class MyInterface extends JPanel {
    JLabel l_x,l_y;
    JTextField t_x,t_y;
    public MyInterface() {
       l_x=new JLabel("x");
       l_y=new JLabel("y");
       t_x=new JTextField(10);
       t_y=new JTextField(10);
       setLayout(new FlowLayout((int) CENTER_ALIGNMENT));
       add(l_x);add(t_x);
       add(l_y);add(t_y);
import java.awt.Dimension;
import javax.swing.JPanel;
* @author sakshi
public class MyJPanel extends JPanel {
    public MyJPanel() {
        setPreferredSize(new Dimension(1000,1000));
import java.awt.Component;
import java.awt.Dimension;
import javax.swing.JScrollPane;
import javax.swing.ScrollPaneConstants;
* @author sakshi
public class MyJScrollPane extends JScrollPane {
    public MyJScrollPane(Component v) {
        super(v,ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        setPreferredSize(new Dimension(500,500));
}

Answer 1

thanks now there are no exceptions
sir how can i call repaint when scrollbars are moved because the screen becomes distorted on moving it
i have added paintComponent method in JPanel.
package introswing;
import java.awt.BorderLayout;
import javax.swing.JApplet;
* @author sakshi
public class MainJA extends JApplet {
    MyInterface in;
    MyJPanel jp1;
    MyJScrollPane jsp;
     * Initialization method that will be called after the applet is loaded
     * into the browser.
    @Override
    public void init() {
        makeGUI();
    // TODO start asynchronous download of heavy resources
    void makeGUI() {
        setLayout(new BorderLayout());
        in = new MyInterface();
         jp1 = new MyJPanel(in);
        jsp = new MyJScrollPane(jp1);
        add(jsp, BorderLayout.CENTER);
        add(in, BorderLayout.SOUTH);
    // TODO overwrite start(), stop() and destroy() methods
package introswing;
import java.awt.FlowLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
* @author sakshi
public class MyInterface extends JPanel {
    JLabel l_x,l_y;
    JTextField t_x,t_y;
    public MyInterface() {
       l_x=new JLabel("x");
       l_y=new JLabel("y");
       t_x=new JTextField(10);
       t_y=new JTextField(10);
       setLayout(new FlowLayout(FlowLayout.CENTER));
       add(l_x);add(t_x);
       add(l_y);add(t_y);
    void setText(int x,int y)
        t_x.setText(String.valueOf(x));  t_y.setText(String.valueOf(y));
     //   System.out.println("setting text");
package introswing;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.JPanel;
* @author sakshi
public class MyJPanel extends JPanel implements MouseMotionListener {
    MyInterface i;
    public MyJPanel(MyInterface in) {
        i=in;
        setPreferredSize(new Dimension(1000,1000));
        addMouseMotionListener(this);
    public void mouseDragged(MouseEvent e) {
      //  throw new UnsupportedOperationException("Not supported yet.");
    public void mouseMoved(MouseEvent e) {
        i.setText(e.getX(), e.getY());
         System.out.println("setting text");
       // throw new UnsupportedOperationException("Not supported yet.");
    public void paintComponent(Graphics g)
        g.drawLine(12,23,66,87);
package introswing;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import javax.swing.JScrollPane;
import javax.swing.ScrollPaneConstants;
* @author sakshi
public class MyJScrollPane extends JScrollPane implements AdjustmentListener {
    Component js;
    public MyJScrollPane(Component v) {
        super(v,ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        setPreferredSize(new Dimension(500,500));
        js=v;
    public void adjustmentValueChanged(AdjustmentEvent e) {
        js.repaint();
        //throw new UnsupportedOperationException("Not supported yet.");
    /*public void paintComponent(Graphics g)
        g.drawLine(12,23,66,87);
}i tried it once using the adjustment listener interface