java - Resize JComboBox when window resizes -

java - Resize JComboBox when window resizes -

i have jframe toppanel, centerpanel , bottompanel. in toppanel have grid 6 columns , 1 row. have fixed sizes of columns. in the column right have jcombobox.

my problem when resize window (make smaller or bigger) jcombobox not resize (which means disappears when window gets little enough, or lot of space around when windows gets large). want jcombobox resize when window does.

my teacher says 1 line of code can prepare it, , have tried figure out night long. can guys help me?

import java.awt.*; import javax.swing.*; public class programme extends jframe { public program(string title) { super(title); setlayout(new borderlayout()); setdefaultcloseoperation(windowconstants.exit_on_close); setsize(840, 500); initcomponents(); setvisible(true); } private void initcomponents() { string[] boxoptions = new string[] {"man", "woman"}; jpanel toppanel = new jpanel(new gridlayout(1,6)); jpanel centerpanel = new jpanel(); jpanel bottompanel = new jpanel(new gridlayout(1,3)); jpanel greenpanel = new jpanel(); jpanel bluepanel= new jpanel(); jpanel blackpanel = new jpanel(); jpanel redpanel= new jpanel(); jpanel yellowpanel = new jpanel(); jpanel comboboxpanel = new jpanel(); jcombobox combobox = new jcombobox(boxoptions); combobox.setselectedindex(0); combobox.setpreferredsize(new dimension(140,40)); greenpanel.setbackground(color.green); bluepanel.setbackground(color.blue); blackpanel.setbackground(color.black); redpanel.setbackground(color.red); yellowpanel.setbackground(color.yellow); greenpanel.setpreferredsize(new dimension(140,40)); bluepanel.setpreferredsize(new dimension(140,40)); blackpanel.setpreferredsize(new dimension(140,40)); redpanel.setpreferredsize(new dimension(140,40)); yellowpanel.setpreferredsize(new dimension(140,40)); comboboxpanel.setpreferredsize(new dimension(140,40)); toppanel.setpreferredsize(new dimension(0,40)); comboboxpanel.add(combobox); toppanel.add(greenpanel); toppanel.add(bluepanel); toppanel.add(blackpanel); toppanel.add(redpanel); toppanel.add(yellowpanel); toppanel.add(comboboxpanel); add(toppanel, borderlayout.page_start); add(centerpanel, borderlayout.center); add(bottompanel, borderlayout.page_end); } public static void main(string args[]) { new program("test"); } }

java jcombobox