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How to add combobox from source code along with drag and drop GUI Java NetBean

I'm starting using java with NetBeans IDE. I'm using drag and dop GUI, it's so easy to use, but I got a problem. I'm writing this code at the contructor:
JComboBox combobox=new JComboBox();
combobox.addItem("Apple");
combobox.addItem("Banana");
for(int i=1;i<=10;i++){
combobox.addItem(i);
}
just right above initComponents(); hoping that my new combobox will shown when I run the project, but it doesn't. Did I do something wrong? Thanks in advance

Yes, you are creating a JComboBox, and yes, you are adding items to it (numeric and int -- that's a problem, but that's a discussion for another day), but no, you're not showing any code where you add this newly created JComboBox to a component that is displayed in the GUI. To display a component in a Swing GUI, it must be created and added to a component that is ultimately displayed in a top-level window, in the "GUI".
So this begs the question, how do you add your created JComboBox to your GUI that you've created with drag and drop code? One way: you could add it to say a JPanel that's already in your GUI, but you will need to do this after initializing components, usually this means after the constructor calls initComponents(), and you'll also need to make sure that this JPanel uses a layout manager that makes it easy for it to accept new components (this means most of the layout managers except NetBean's default layout, GroupLayout).
There are other issues, such as whether or not the container holding your JComboBox is large enough to display it, but the best suggestion that I can give is for you to go through the Swing tutorials, and hit especially hard the layout manager section. You can find links to the Swing tutorials and other Swing resources here: Swing Info.

external panels in swing

I have something like this...
Its a bunch of JLabels within JPanels inside a
--JFrame
--JPanel
--Set<JPanel>
--JLabel object contained in each JPanel object cotained in the set
I want to create an external panel/frame so that each time I hover over each individual JPanel, a new frame/panel pops up giving me some data. This will essentially overlap over the JFrame.
Its pretty brief but I just need some guidance as to what I need to look up.

Maybe you can just use JToolTip. When the mouse hovers over the label for a couple of seconds it will display automatically. See the section from the Swing tutorial on How to Use Tool Tips.
Or if you want something more complicated use a MouseListener. On mouseEntered() you can display a JPopupMenu or an undecorated JDialog.
You can start by reading the Swing tutorial on How to Write a Mouse Listener.

JPanel data getting changed on mouse click

I am using three JButtons in my swing application. When I click on each button, the corresponding data (formatted in JTable with JScrollPane) will display on JPanel.
Problem: when I resize the JFrame, the JPanel is replacing with default button (the button which i was clicked first) information instead of current JButton information.
My sample code:
jbutton1.addActionListener(this);
jbutton2.addActionListener(this);
public void actioPerformed(ActionEvent e){
if(e.getActionCommand.equals("button1"))
JPanel.add(table1);
}
if(e.getActionCommand.equals("button2"))
JPanel.add(table1);
}.......

Resizing the JPanel will not suddenly replace components or add other components to the panel.
My best guess (and it is a guess due to the limited information in the question) is that none of your buttons actually work and just show the wrong information.
The code you posted only contains an add without any revalidation of the layout. Consult the javadoc of the Container#add method. When you resize, the layout gets revalidated and you see what is actually contained in the JPanel.
Possible solutions:
Call invalidate and repaint on your panel as well in your ActionListener
Use a CardLayout to switch between the different components
I personally prefer the CardLayout option, but it might depend a bit on the situation.
Note that in the code you posted, you add table1 for both buttons. Might be a copy-paste problem, or a problem with your actual code.

I was unable express problem clearly.Sorry for your inconvenience.
JPanel.removeAll() method has fixed my problem.
I added this method before adding any new component to JPanel. That fixes JPanel unexpected behavior.

table generation runtime

Hello to all Stackoverflow developers thanks for helping me .
I am working on a swing project .In which , i have to add a jinternal frame on jframe . i am adding the jinternal frame by calling method
Container.add(jinternalframe1);
the internalframe is being added but its moving , i want to disable the movement of the jinternalframe. on clicking a button on jinternalframe i want to add a JList and JTable on the previous frame window
I am calling the method
frame1.cp.add(list1);
frame1.cp.add(table1);
while clicking on jlist the table should be removed and new table should be generated. I am writing the following code for it
ms.cp.remove(table);
table= new JTable(String title, Object obj[][]);
add(table);
by doing so jtable is not being removed from container plz suggest me whats wrong in my code

It sounds like your Container is using a layout manager which is deciding on how the internal frame should be displayed. JInternalFrame is designed to work with containers that don't have a layout manager, most notably, the JDesktopPane. For information check out How to Use Internal Frames
It sounds like you actually want to use a dialog instead of a internal frame
Why are reconstructing the table from scratch? Simply update the model. Besides, you remove the table from ms.cp using ms.cp.remove(table) and then add it to something else, no wonder it never shows up. See How to use Tables for more information.

Small Window Over Components

I already look at java library and dont know what to use to do this..
I already tryed JInternalFrame but thats not what I really want.. because it needs to be added to a JDesktopPanel right??
And in my program I have a JFrame with content pane using BorderLayout..
Then on borderlayout center I have a JTextArea, on borderlayout east I have a list.. and on borderlayout south I have a JPanel..
What I want is, when I do a certain action, it will pop up a "mini window" where I need to choose something.. u see?
and if I create JDesktopLane it will overlap what I have on the container..
the window will be made by my like a color chooser pallete , like a grid with colors.. and a label on top saying some text..
I just dont know how to make a "window" over the other components, and users can still drag over the frame, and interact with all the other components.. the jtextarea and such..
I guess you understood, thanks alot in advance!!
If u dont understand something please tell me, I really want to do this :)
Just dont know what to use..
Thanks again ;)

Have you tried JDialog?

It's because Jdialog are not component to be add in a JFrame, it's an independant thing running on it's own
if you use JDialog, the construct parameter parent indicate wich frame the JDialog is related to.

The typical class for this task is JWindow, a borderless top-level window that can be freely positioned. You could use SwingUtilities.getPointFromComponent to get the screen coordinates for a realized coordinate.
Top-level windows (JFrame, JDialog, JWindow) are not added to containers. They can get other windows as parent.
I dont want to use another JFrame.. that is kinda bad for code, its a small window with a simple function..
Structure your code so you can read it, others can read it, and you can debug it easily (the latter is a result from the first). A low class count is useless and -most of the time- contraproductive.
Why should another JFrame (or other window) be bad?
If you absolutely want to avoid opening top level windows (e.g. to avoid applet warning icons or to implement a special kind of user interface) you could use a JLayeredPane to add additional JPanels above your existing GUI elements.