GUI in Java.. generating a run time component

Something like that:

// Assuming myOrigTextField is your original JTextField
int howMany = Integer.parseInt(myOrigTextField.getText());
JTextField[] jtfs = new JTextField[howMany];

for (int i = 0; i < jtfs.length; ++i) {
   jtfs[i] = new JTextField();
   myPanelToAddThem.add(jtfs[i]);
}

Create the text field objects, add them to your container.

Use a loop to do this with an arbitrary number.

Post some code and your specific problems for more help.

Roughly assuming some thing about layout manager you're using I'd say this:

public List<JTextField> addComponents( int number ) {
    List<JTextField> fields = new ArrayList<JTextField>( number );
    for( int i = 0; i < number; i++ ) {
        fields.add( new JTextField() );
        panelToAddComponentsTo.add( fields.get( i ) );
    }
    return fields;
}

if the user presses enter I want ? text feilds to be generated in the same User Interface

You add an ActionListener to the text field. The ActionListener will be invoked when the Enter key is pressed.

In the ActionListener code you need to parse the number entered and then loop to create and add the text fields to your panel:

for (...)
{
    panel.add( new JTextField(...) );
}

panel.revalidate(); // needed when dynamically adding/removing components
panel.repaint(); // sometimes needed