How to close JInternal Frame Dynamically when object is created at runtime

I am opening a JInternal Frame by getting its name from JTextField and ** then creates its object at runtime**, the problem is that if I write 10 times different Internal Frame name in textBox and then click the button it opens the new JInternal Frame everytime.
Now i want whenever a new JInternal Frame is open, the previous JInternalFrame should be close automatically.
I know it's pretty easy to do that but my case is difficult because of i create its object at run time, how can i do it.

My code behine the Button is following

private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) {                                         

    String st = TextField.getText().toString(); // in TextField i enter the JInternal Frame Name
    String clazzname = "practice."+st;         // practice is the package name
    try
   {
     JInternalFrame obj1 = (JInternalFrame) Class.forName( clazzname ).newInstance();
      obj1.setVisible(true);
 jPanel1.add(obj1);                // now in there i want that whenever i click the button , it check either is there any Jinternal frame is open already or not  if yes then close the previously open JFrame 

 }
  catch(Exception e)
  {
    System.out.println("error "+e);
 }

   }

Solution

I know it's pretty easy to do that but my case is difficult because i creats its object at run time, how can i do it.

There's nothing magical about runtime that makes this any different from how you'd normally close it. The secret is in having a reference to the JInternalFrame readily available. A solution is to use a JInternalFrame field, a non-static instance variable, to hold the reference and not use a local variable as you're currently doing. The key here is to understand that references are what matter, much more so than variables. If you need a reference variable that persists when the method ends, then the variable cannot be declared within the method but should be on class scale.

Something like:

public class MyGui {
    // instance field to hold reference to currently displayed JInternalFrame
    private JInternalFrame currentInternalFrame = null;

    private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) {        
        if (currentInternalFrame != null) {
            currentInternalFrame.dispose(); // clear current one
        }

        String st = TextField.getText().toString(); // in TextField i enter the JInternal Frame Name
        String clazzname = "practice."+st;         // practice is the package name  
        try {

            // JInternalFrame obj1 = (JInternalFrame) Class.forName( clazzname ).newInstance();

            currentInternalFrame = (JInternalFrame) Class.forName( clazzname ).newInstance();

            currentInternalFrame.setVisible(true);
            jPanel1.add(currentInternalFrame);           
        } catch(Exception e) {
            System.out.println("error "+e);
        }
    } 
}

Note that this code has not been tested and is not here for a copy-and paste solution but to give you a general idea.

Another unrelated issue is on program design: users don't usually like windows opening and closing, and perhaps a better program structure for your user is to swap JPanel views via a CardLayout (please read the CardLayout Tutorial for more on this).