NullPointerException in swing at actionPerformed - swing

Question

This is a login form for a slot machine game which will evoke a "NextPage" object. I don't think this LoginDemo.java code has to do anything with the error but I prefer to post the entire code. Thanks in advance..
//LoginDemo.java
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Login extends JFrame implements ActionListener
{
JButton SUBMIT;
JPanel panel;
JLabel label1,label2;
final JTextField text1,text2;
Login()
{
label1 = new JLabel();
label1.setText("Username:");
label1.setBounds(50,50,100,30);
text1 = new JTextField(15);
text1.setBounds(250,50,100,30);
label2 = new JLabel();
label2.setText("Password:");
label2.setBounds(50,250,100,30);
text2 = new JPasswordField(15);
text2.setBounds(250,250,100,30);
//this.setLayout(new BorderLayout());
SUBMIT=new JButton("SUBMIT");
SUBMIT.setBounds(350,350,100,30);
// panel=new JPanel(new GridLayout(3,1));
panel=new JPanel(null);
panel.setBounds(50,50,1000,1000);
// panel.setLayout(new FlowLayout());
panel.add(label1);
panel.add(text1);
panel.add(label2);
panel.add(text2);
panel.add(SUBMIT);
add(panel,BorderLayout.CENTER);
SUBMIT.addActionListener(this);
setTitle("LOGIN FORM");
}
public void actionPerformed(ActionEvent ae)
{
String value1=text1.getText();
String value2=text2.getText();
if (value1.equals("a") && value2.equals("a"))
{
NextPage page=new NextPage();
page.setVisible(true);
//JLabel label = new JLabel("Welcome:"+value1);
// page.getContentPane().add(label);
setVisible(false);
}
else
{
//System.out.println("enter the valid username and password");
JOptionPane.showMessageDialog(this,"Incorrect login or password","Error",JOptionPane.ERROR_MESSAGE);
}
}
}
class LoginDemo
{
public static void main(String arg[])
{
try
{
Login frame=new Login();
frame.setSize(1000,1000);
frame.setVisible(true);
}
catch(Exception e)
{
JOptionPane.showMessageDialog(null, e.getMessage());
}
}
}
//NextPage.java
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.util.Random;
import java.sql.*;
import java.lang.*;
import java.awt.image.*;
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import java.io.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class NextPage extends JFrame implements Runnable, ActionListener
{
BufferedImage img1,i0,i1,i2,i3,i4,i5,i6,i7,i8,i9,i10,i11,i12,star1;
JFrame f1;
Thread t1,t2,t3;
int x1,y1,i,j,k,l,m,n,r1,r2,r3;
JButton b1;
Random r=new Random();
TextField tf1;
JPanel p1;
NextPage()
{
setBounds(50,50,1000,1000);
p1=(JPanel)(getContentPane());
p1.setBounds(50,50,1000, 1000);
p1.setLayout(null);
//tf1=new TextField(20);
//tf1.setBounds(50,50,100,30);
setDefaultCloseOperation(javax.swing.WindowConstants.DISPOSE_ON_CLOSE);
setTitle("Welcome");
b1=new JButton("START");
//p1.add(tf1);
b1.setBounds(150,400,100,30);
//try{
b1.addActionListener(this);
//}
/*catch(Exception e)
{
System.out.println(""+e);
}*/
add(b1);
setVisible(true);
try
{
i0=ImageIO.read(new File("tea.jpg"));
i1=ImageIO.read(new File("coffee.jpg"));
i2=ImageIO.read(new File("bhel.jpg"));
i3=ImageIO.read(new File("pizza.jpg"));
i4=ImageIO.read(new File("icecream.jpg"));
i5=ImageIO.read(new File("dosa.jpg"));
i6=ImageIO.read(new File("idli.jpg"));
i7=ImageIO.read(new File("panipuri.jpg"));
i8=ImageIO.read(new File("orange.jpg"));
i9=ImageIO.read(new File("watermelon.jpg"));
i10=ImageIO.read(new File("pavbhaji.jpg"));
i11=ImageIO.read(new File("noodles.jpg"));
i12=ImageIO.read(new File("sandwich.jpg"));
}
catch (IOException ie)
{
System.out.println("Error:"+ie.getMessage());
}
j=0; m=0; n=0;
r1= r.nextInt(13);
r2= r.nextInt(13);
r3= r.nextInt(13);
}
public void init()
{
t1=new Thread(this);
t2=new Thread(this);
t3=new Thread(this);
}
public void start()
{
t2.start();
t3.start();
}
public void run()
{
try
{
if(Thread.currentThread()==t1)
for(j=0; j<150; j++)
//for(i=0; i<=150; i+=20)
{
r1= r.nextInt(13);
repaint();
t1.sleep(10);
}
if(Thread.currentThread()==t2)
for(m=0; m<160; m++)
//for(k=0; k<=150; k+=20)
{
r2= r.nextInt(13);
repaint();
t2.sleep(10);
}
if(Thread.currentThread()==t3)
for(n=0; n<170; n++)
//for(l=0; l<=150; l+=20)
{
r3= r.nextInt(13);
repaint();
t3.sleep(10);
}
}
catch(Exception e)
{
System.out.println(""+e);
}
}
public void paint(Graphics g)
{
g.setColor(Color.blue);
g.drawRect(50,300,150,80);
g.drawRect(200,300,150,80);
g.drawRect(350,300,150,80);
switch(r1)
{
case 0: g.drawImage(i0,65,300,this);
break;
case 1: g.drawImage(i1,65,300,this);
break;
case 2: g.drawImage(i2,65,300,this);
break;
case 3: g.drawImage(i3,65,300,this);
break;
case 4: g.drawImage(i4,65,300,this);
break;
case 5: g.drawImage(i5,65,300,this);
break;
case 6: g.drawImage(i6,65,300,this);
break;
case 7: g.drawImage(i7,65,300,this);
break;
case 8: g.drawImage(i8,65,300,this);
break;
case 9: g.drawImage(i9,65,300,this);
break;
case 10: g.drawImage(i10,65,300,this);
break;
case 11: g.drawImage(i11,65,300,this);
break;
case 12: g.drawImage(i12,65,300,this);
break;
}
switch(r2)
{
case 0: g.drawImage(i0,215,300,this);
break;
case 1: g.drawImage(i1,215,300,this);
break;
case 2: g.drawImage(i2,215,300,this);
break;
case 3: g.drawImage(i3,215,300,this);
break;
case 4: g.drawImage(i4,215,300,this);
break;
case 5: g.drawImage(i5,215,300,this);
break;
case 6: g.drawImage(i6,215,300,this);
break;
case 7: g.drawImage(i7,215,300,this);
break;
case 8: g.drawImage(i8,215,300,this);
break;
case 9: g.drawImage(i9,215,300,this);
break;
case 10: g.drawImage(i10,215,300,this);
break;
case 11: g.drawImage(i11,215,300,this);
break;
case 12: g.drawImage(i12,215,300,this);
break;
}
switch(r3)
{
case 0: g.drawImage(i0,365,300,this);
break;
case 1: g.drawImage(i1,365,300,this);
break;
case 2: g.drawImage(i2,365,300,this);
break;
case 3: g.drawImage(i3,365,300,this);
break;
case 4: g.drawImage(i4,365,300,this);
break;
case 5: g.drawImage(i5,365,300,this);
break;
case 6: g.drawImage(i6,365,300,this);
break;
case 7: g.drawImage(i7,365,300,this);
break;
case 8: g.drawImage(i8,365,300,this);
break;
case 9: g.drawImage(i9,365,300,this);
break;
case 10: g.drawImage(i10,365,300,this);
break;
case 11: g.drawImage(i11,365,300,this);
break;
case 12: g.drawImage(i12,365,300,this);
break;
}
}
public void actionPerformed(ActionEvent ae)
{
if(ae.getSource()==b1)
t1.start();
}
/*public static void main(String args[])
{
NextPage o=new NextPage();
}*/
}
}
Here are the exceptions that I get-
F:\java\jdk\bin>java LoginDemo
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at NextPage.actionPerformed(NextPage.java:235)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
atjavax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6289)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6054)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4652)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4482)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4482)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:644)
at java.awt.EventQueue.access$000(EventQueue.java:85)
at java.awt.EventQueue$1.run(EventQueue.java:603)
at java.awt.EventQueue$1.run(EventQueue.java:601)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87
at
java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98
at java.awt.EventQueue$2.run(EventQueue.java:617)
at java.awt.EventQueue$2.run(EventQueue.java:615)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87
at java.awt.EventQueue.dispatchEvent(EventQueue.java:614)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Can't get any solution.. I am a learner..please help..

Answer 1

You used the variable t1 to start the thread that should be assigned to this variable. How ever the function init() that creates the instance of the thread that is assigned to this variable is never called. There for t1 is null and calling any function on a null object causes the NullPointerException.
Simply call the init() function. I think the original idea was to call it within the constructor and you simply forgot to insert it.
For future question please consider only posting the lines close to the point where the StackTrace reports the error. To find that spots of interest look into the StackTrace and look for entries in classes you wrote. In this case NextPage.actionPerformed(NextPage.java:235) is a point of interest. In your question best mark those spots to get a good resolution quickly.

Answer 2

You do not call the init method, hence your t1 variable is still null when you enter the actionPerformed method.
This is rather obvious from the stacktrace (there is only one thing that can be null on that line), and if not obvious from the stacktrace a debugger would have shown this immediately. Way faster then creating a post with hundreds of lines of irrelevant code