There is a Frame containing a button n i want to create
another window whenever the button is pressed.Is it possible ?

I tried it by writing the creation of frame in
actionPerformed() of the ActionListener interface,but it didn't work.

Yes it is possible. Here is a fragment that show you
how you should do it...
.......
JButton loginButton = new JButton("ClickMe");
loginButton.addActionListener(

new ActionListener() { // inner class

public void actionPerformed(ActionEvent event) {
MyOtherFrame myScreen = new MyOtherFrame();

}

} // end inner class

); // end call to addActionListener

.........
Note:
MyOtherFrame is another class defined in their own
class file. What you can do is copy the class you
already have and rename the copy MyOtherFrame. Just a
suggestion I think will be easier to help  you, if you
can post the program or fragment where you're having
problem(s)!

you can do this incrementing a variable if the button is clicked and if the
variable is greater than certain number(10) then a following code is executed

Here is a simple and primitive example  for you.Don't forget to use setVisible
method of JFrame.
Regards

public class JFrmMainWindow extends JFrame implements
java.awt.event.ActionListener{
JButton newWindow = new JButton();
public JFrmMainWindow() {
init();
}
public static void main(String[] args) {
JFrmMainWindow jFrmMainWindow = new JFrmMainWindow();

}
private void init() {
newWindow.setBounds(new Rectangle(134, 211, 132, 45));
newWindow.setText("New Window");
newWindow.addActionListener(this);
this.setSize(500,400);
this.getContentPane().setLayout(null);
this.getContentPane().add(newWindow, null);
this.setVisible(true);
}

private void createNewWindowAndShowIt(){
JFrame newWindow=new JFrame();
newWindow.setSize(100,100);
newWindow.setVisible(true);
}
public void actionPerformed(ActionEvent e) {
createNewWindowAndShowIt();
}
}

There is a window,which contains a button n the code
is written in such a way that whenever the button is pressed , it
displays another window,but the problem is i want the child window
to be created only once evenif i press the button 10 times or
infinite number of times.

How is it possible , plz do mail me.

I have one more doubt , at wht points of time will a
person encounter NullPointerException.

1. Use singleton design pattern(have a look to
http://www.patterndepot.com/put/8/Singleton.PDF) for creating if you want to
create only one instance of a class.
If it is not easy to understand you can do sometihng like that
Use a handle in the class which listens the action of your button but it should
be static (such as static boolean isWindowCreated)
Set this flag when you create a window to true.And control the state of this
flag before handling the event of your button.An example  code is in below:
public class JFrmMainWindow extends JFrame implements

static boolean isWindowCreated=false;
java.awt.event.ActionListener{
JButton newWindow = new JButton();
public JFrmMainWindow() {
init();
}
public static void main(String[] args) {
JFrmMainWindow jFrmMainWindow = new JFrmMainWindow();

}
private void init() {
newWindow.setBounds(new Rectangle(134, 211, 132, 45));
newWindow.setText("New Window");
newWindow.addActionListener(this);
this.setSize(500,400);
this.getContentPane().setLayout(null);
this.getContentPane().add(newWindow, null);
this.setVisible(true);
}

private void createNewWindowAndShowIt(){
if(!isWindowCreated){
JFrame newWindow=new JFrame();
newWindow.setSize(100,100);
newWindow.setVisible(true);
isWindowCreated=true;
}
}
public void actionPerformed(ActionEvent e) {
createNewWindowAndShowIt();
}
}

2. Null pointer exception means you did not create an instance but you are
trying to use it.
E.g
SimpleClass anInstanceOfSimpleClass;
anInstanceOfSimpleClass.makeASimpleThing();

3.You can navigate a folder with javax.swing.JFileChooser
Maybe you can navigate a web page with Runtime.getRuntime().exec method you can
execute iexplore but you can't naigate a web a page with swing  directly.maybe
there can be some libs maybe you can look to www.sf.net

Your questions are not clear maybe you can put some example codes to your mails

to me your problem looks simple....i will tell u how can u solve it..
First thing....dont a new window when you press the button. create the window
only once and
keeep that window instance as global. soo u just neeed to show the window whenn
u click the button.
hope u got wat m saying.......and null pointer exception occurs when you declare
a variable or object but you do not initialize it... and also when you are
tryinng to read  an object which has null value...that object can b a string can
b and array or anything which is null or empty.

1.to create or open a single window check for boolean condition if frame enabled
or shown then display your window


2.nullpointerexception will be thrown when u refer to a object which is not
available at runtime.

Is it possible to create Hyperlinks in Java using
the concept of "Swing". If yes, how ?

Can we achieve navigation using Swing,i mean to ask,
is it possible to navigate to a file of a folder or to any webpage
using Swing.

what exactly do you mean, navigating through the landscape using
Swing? Do you want to build something the like Internet Explorer? Or
the File Manager from Windows 3.1? Or download a web page at a given
URL? What exactly do you want to do?

There is a program , which displays a window
whenever a button is pressed but the problem is , i want the window
to be displayed only once even if i click it 10 times or infinite
times . How can i achieve that .

The easiest way is to use a static method of the class which uses a
static counter (or flag) variable; the principle goes like this:

1) In your class, declare a static int (or boolean) alreadyCreated.
2) Define a static method which first makes sure that it's called
only once (not twice or more often in parallel executions, that means
you have to execute this method in a single thread always).
3) This method checks whether the flag variable already has been set
to 1 (or greater). If so, it returns null.
4) Otherwise (flag is still 0 or false, depending on the type of the
variable) create a new instance of this class and return it to the
caller _after_ incrementing the counter (or setting the flag to true).

This sort of methods (static methods creating instances of their
class) is called factory methods.

When will we get a NullPointerException in the
concept of Swing ?

Is it correct n whether it works , if we write an
actionPerformed() for a Button and a TextField in an inner class.

a NullPointerException is thrown if you try to reference an instance
of any class where the reference is still null.

Would you please explain in a bit more detail what you mean by the
Button and the TextField? Without more info we can't give more than
general hints about your possible problems.