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JComboBox changinging other JComboBoxes (multiple times) error

need some help with ComboBoxes in Java. Looked through similar questions, found one slightly related, but not what im dealing with.
I need to load certain arrays into combo boxes depending on the items selected in the precious combo box:
think getting some procedure done at a medical center: Choose a procedure->get a list of doctors who do it, choose a doctor->get a list of available hours etc.
A single choice is working fine(whether it's "procedure->list of doctors", or "list of doctors->their working hours"), but doing more than a single one of those changes doesn't work.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Arrays;
public class GUIbandymas extends JFrame {
String[] start={"Choose","Choice1", "Choice2"};
String[] Option1={"Choose","A1"};
String[] Option2={"Choose","A2","A3"};
String[] Option3={"Choose","a","b","c","d"};
String[] Option4={"Choose","1","2","3","4"};
String[] Option5={"Choose","I","II","III","IV"};
String[] pradinis={"Pasirinkite Laika"};
String[] p1={"Pasirinkite Gydytoja"};
static double kainaR;
static double kainaK;
JComboBox<String> G=new JComboBox<String>(p1);
JComboBox<String> proc;
JComboBox<String> laikas=new JComboBox<String>(pradinis);
JComboBox<String> minutes;
JButton button = new JButton ("Registuotis");
JLabel label = new JLabel("Moketi uz vizita");
JLabel suma = new JLabel();
public GUIbandymas() throws Exception {
setValueProc(start);
frame();
}
public void frame()
{
JFrame frame = new JFrame();
frame.setVisible(true);
frame.setSize(500,300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
panel.add(proc);
panel.add(G);
panel.add(laikas);
panel.add(button);
button.setEnabled(false);
//panel.add(minutes);
frame.add(panel);
panel.add(label);
panel.add(suma);
proc.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e) {
if(proc.getSelectedItem().toString().equals("Choice1"))
{
setGyd(Option1);
}
if(proc.getSelectedItem().toString().equals("Choice2"))
{
setGyd(Option2);
}
}
});
G.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent a) {
if(G.getSelectedItem().toString().equals("A1"))
{
setLaikas(Option3);
}
if(G.getSelectedItem().toString().equals("A2"))
{
setLaikas(Option4);
}
if(G.getSelectedItem().toString().equals("A3"))
{
setLaikas(Option5);
}
}
});//JComboBox
}
public void setGyd(String[] s)
{
G.removeAllItems();
for(int i=0; i<s.length; i++)
{
G.addItem(s[i]);
}
}
public void setValueProc(String[] sarasas)
{
proc=new JComboBox<String>(sarasas);
}
public void setLaikas(String[] sarasas)
{
laikas.removeAllItems();
for(int i=0; i<sarasas.length; i++)
{
laikas.addItem(sarasas[i]);
}
}
}
Im in a dire need of any suggestions and possible fixes, im inclined to think that it has something to do with action listeners, since methods do work, but im at a loss since i cant determine what is it.
EDITED: the actual code should work, seems like there is no unneeded things from other files left.
NOTE: this is work with GUI, just launch it in you main() :)

While I don't really like the if-else approach you're using, it should work just fine. I agree with rrirower's suggestion that you should look at using a data model instead. Especially if you get a lot of choices, since the code turns messy quite fast.
The problem with your code is that you run into NullPointerException when rebuilding the combobox items. The reason for this is that G.actionPerformed() is called when you remove/add items. After you have removed all items (before you start adding new ones), G.getSelectedItem() will return null.
If you code a little bit more defensively, then it works as expected:
proc.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object selectedItem = proc.getSelectedItem();
if ("Choice1".equals(selectedItem)) {
setGyd(Option1);
}
if ("Choice2".equals(selectedItem)) {
setGyd(Option2);
}
}
});
G.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent a) {
Object selectedItem = G.getSelectedItem();
if ("A1".equals(selectedItem)) {
setLaikas(Option3);
}
if ("A2".equals(selectedItem)) {
setLaikas(Option4);
}
if ("A3".equals(selectedItem)) {
setLaikas(Option5);
}
}
});//JComboBox
Instead of checking for null's, I just flipped the equals and skipped the unnecessary toString() (they are already strings, that's what you put in there).
Another thing, a pet peeve of mine, please follow the normal java code convention for all your class, field and method names. You're almost there, but Option1 etc. should start with lowercase. G should probably have a more descriptive name, as well as start with lowercase.
Finally, I didn't understand why you both create a JFrame in the constructor and extend JFrame in your class. You should choose one or the other.

You don't appear to be using a data model for the combo box. The data model controls the internal list of items. Have a look at this for more info.

JTable won't listen to Doubleclicks

I´m trying to implement an undo (and redo) function for an editable JTable with the default components. The JTable has an extra class to specify its properties called SpecifiedJTable.
To do so I wanted to grab the moment when a cell is doubleclicked (i.e. the moment when a cell is chosen/marked to be edited) to push the information in the cell and its coordinates onto the stack.
This should be done by a MouseListener ...at least that was my idea.
I tried this (standing in the constructor of my SpecifiedJTable class)
class JTableSpecified extends JTable {
private static final long serialVersionUID = 1L;
private int c; // the currently selected column
private int r; // the currently selected row
public JTableSpecified(String[][] obj, String[] columnNames) {
super(obj, columnNames); // constructs the real table
// makes that you can only select one row at a time
this.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
// makes that columns are not squeezed
this.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
// forbids to rearrange the columns
getTableHeader().setReorderingAllowed(false);
// adds action listener
this.getModel().addTableModelListener(new TableModelListener() {
public void tableChanged(TableModelEvent e) {
r = getSelectedRow();
c = getSelectedColumn();
// get the String at row r and column c
String s = (String) getValueAt(r, c);
if (jobDisplayed) jobSwitch(c, s);
else resSwitch(c, s);
}
});
this.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
if (e.getClickCount() == 2) {
System.out.println("test");
}
}
});
}
}
but somehow the clickCounter doesn´t want to reach anything that´s higher than 1.
I am glad about any answer and help. Thanks.

The problem you are experiencing is related to use of mouseClicked() rather than using mousePressed(). In this case it appears to be very hard to increase the click counter, yet still it is possible. It took me lots of clicking and also mouse movement to increase the click counter over 1. You could try it by yourself, in your code. To get the counter over 1 you need to go crazy on the mouse by pressing & releasing fast while moving the mouse from cell to cell at the same time (or maybe I was just luckily clicking between the cells?).
As you can see in this fully working sample, made from your code, two mouse presses, using the mousePressed() method are being detected just fine.
public class JTableSpecified extends JTable {
private static final long serialVersionUID = 1L;
public JTableSpecified(String[][] obj, String[] columnNames) {
super(obj, columnNames); // constructs the real table
// makes that you can only select one row at a time
this.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
// makes that columns are not squeezed
this.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
// forbids to rearrange the columns
getTableHeader().setReorderingAllowed(false);
// adds action listener
this.getModel().addTableModelListener(new TableModelListener() {
#Override
public void tableChanged(TableModelEvent e) {
}
});
this.addMouseListener(new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
if (e.getClickCount() == 2) {
System.out.println("test");
}
System.out.println("e.getClickCount() = " + e.getClickCount());
}
});
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JPanel panel = new JPanel();
panel.add(new JTableSpecified(new String[][]{{"oi", "oi2"}, {"oi3", "oi4"}}, new String[]{"Col1", "Col2"}));
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(panel);
f.pack();
f.setVisible(true);
}
});
}
}
Conclusion: Maybe you in fact want to use the mousePressed() method?

This answer extends Boro´s answer.
To catch every case that enables the user to edit the table I will also need to add a KeyListener for F2 (which has the same effect as double clicking onto a cell) and disable the automatic cell editing by pressing any key.
I just added it to the constructor right behind the mouseListener (see above)
// forbids the editing by striking a key
this.putClientProperty("JTable.autoStartsEdit", Boolean.FALSE);
// keyListener to react on pressing F2 (key code 113)
this.addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == 113) System.out.println("test");
}
});

The BasicTableUI is responding to the double-click by going into an edit mode on the cell that was double-clicked. It does lots of complicated stuff, part of which involves creating a JTextField (or other component) to allow the data to be edited, and then preventing the mouse click event from propagating any further.
If your table, or that table cell, is not editable, you can easily capture mouse events with click count 2, 3, 4, .... But since you want your table to be editable, you need a different approach.
One idea would be to override JTable.editCellAt()
A better idea is to forget about messing with the JTable and instead listen for data changes on the table model itself.

the error in the code is that the mouseClicked method is called as soon as the first click takes place. when a double click takes place the mouseClicked method is called again. you can place a static variable (or a class variable) for the earlier click event storing the time (using the e.getWhen() method).
Check for the time difference and if it's small enough, execute your actions (I'd suggest calling a doubleClick method).
you may have to implement mouse listener in your class JTableSpecified since a static variable might not be placed in your existing code.

Stopping JPopupMenu stealing the focus

I have a JTextField for which I'm hoping to suggest results to match the user's input. I'm displaying these suggestions in a JList contained within a JPopupMenu.
However, when opening the popup menu programmatically via show(Component invoker, int x, int y), the focus is getting taken from the JTextField.
Strangely enough, if I call setVisible(true) instead, the focus is not stolen; but then the JPopupMenu is not attached to any panel, and when minimizing the application whilst the box is open, it stays painted on the window.
I've also tried to reset the focus to the JTextField using requestFocus(), but then I have to restore the caret position using SwingUtilities.invokeLater(), and the invoke later side of things is giving the user a slight margin to mess around with the existing contents / overwrite it / or do other unpredictable things.
The code I've got is effectively:
JTextField field = new JTextField();
JPopupMenu menu = new JPopupMenu();
field.addKeyListener(new KeyAdapter() {
public void keyTyped(KeyEvent e) {
JList list = getAListOfResults();
menu.add(list);
menu.show(field, 0, field.getHeight());
}
});
Can anyone suggest the best avenue to go down to show the JPopupMenu programmatically whilst preserving the focus on the JTextField?

The technical answer is to set the popup's focusable property to false:
popup.setFocusable(false);
The implication is that the textField has to take over all keyboard and mouse-triggered actions that are normally handled by the list itself, sosmething like:
final JList list = new JList(Locale.getAvailableLocales());
final JPopupMenu popup = new JPopupMenu();
popup.add(new JScrollPane(list));
popup.setFocusable(false);
final JTextField field = new JTextField(20);
Action down = new AbstractAction("nextElement") {
#Override
public void actionPerformed(ActionEvent e) {
int next = Math.min(list.getSelectedIndex() + 1,
list.getModel().getSize() - 1);
list.setSelectedIndex(next);
list.ensureIndexIsVisible(next);
}
};
field.getActionMap().put("nextElement", down);
field.getInputMap().put(
KeyStroke.getKeyStroke("DOWN"), "nextElement");
As your context is very similar to a JComboBox, you might consider having a look into the sources of BasicComboBoxUI and BasicComboPopup.
Edit
Just for fun, the following is not answering the focus question :-) Instead, it demonstrates how to use a sortable/filterable JXList to show only the options in the dropdown which correspond to the typed text (here with a starts-with rule)
// instantiate a sortable JXList
final JXList list = new JXList(Locale.getAvailableLocales(), true);
list.setSortOrder(SortOrder.ASCENDING);
final JPopupMenu popup = new JPopupMenu();
popup.add(new JScrollPane(list));
popup.setFocusable(false);
final JTextField field = new JTextField(20);
// instantiate a PatternModel to map text --> pattern
final PatternModel model = new PatternModel();
model.setMatchRule(PatternModel.MATCH_RULE_STARTSWITH);
// listener which to update the list's RowFilter on changes to the model's pattern property
PropertyChangeListener modelListener = new PropertyChangeListener() {
#Override
public void propertyChange(PropertyChangeEvent evt) {
if ("pattern".equals(evt.getPropertyName())) {
updateFilter((Pattern) evt.getNewValue());
}
}
private void updateFilter(Pattern newValue) {
RowFilter<Object, Integer> filter = null;
if (newValue != null) {
filter = RowFilters.regexFilter(newValue);
}
list.setRowFilter(filter);
}
};
model.addPropertyChangeListener(modelListener);
// DocumentListener to update the model's rawtext property on changes to the field
DocumentListener documentListener = new DocumentListener() {
#Override
public void removeUpdate(DocumentEvent e) {
updateAfterDocumentChange();
}
#Override
public void insertUpdate(DocumentEvent e) {
updateAfterDocumentChange();
}
private void updateAfterDocumentChange() {
if (!popup.isVisible()) {
popup.show(field, 0, field.getHeight());
}
model.setRawText(field.getText());
}
#Override
public void changedUpdate(DocumentEvent e) {
}
};
field.getDocument().addDocumentListener(documentListener);

It looks straight forward to me. Add the following
field.requestFocus();
after
menu.add(list);
menu.show(field, 0, field.getHeight());
Of course, you will have to code for when to hide the popup etc based on what is going on with the JTextField.
i.e;
menu.show(field, field.getX(), field.getY()+field.getHeight());
menu.setVisible(true);
field.requestFocus();

You may take a look to JXSearchField, which is part of xswingx

Cursor icon does not change after triggering setCursor method

There is a JTable in my application with resizable header columns. Normally when I move the cursor over table header for resizing, the cursor icon changes to resize arrow, like <-->.
But things are different in the following scenario.
There is a button action in the same Frame, and during action performed, I am setting the cursor to busy icon and change it back to default cursor once the action is completed, using Container.setCursor(Cursor cursor) method.
Sometimes if I move the cursor over table header of resizing, after a button action, the cursor icon does not change to resize arrow, cursor does not change at all.
Can this be considered as a bug in Java Swing or is there a solution for this issue?
Update : Sample code attached
import java.util.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class ColumnResizeIconTest extends JFrame {
JScrollPane scrollPane;
JTable table;
JButton button;
public ColumnResizeIconTest() {
setLayout(new BorderLayout());
addComponents();
setSize(300,300);
}
private void addComponents() {
addButton();
addTable();
}
private void addButton() {
button = new JButton("Click Me");
button.addActionListener( new ActionListener() {
public void actionPerformed(ActionEvent ae) {
setWaitCursor();
for(int i=0; i<2000; i++) {
System.out.print(i);
}
setDefaultCursor();
}
});
add(button, BorderLayout.NORTH);
}
private void addTable() {
scrollPane = new JScrollPane(createTable());
add(scrollPane, BorderLayout.CENTER);
}
private JTable createTable() {
Object[][] cellData = { { "1-1", "1-2","1-3" }, { "2-1", "2-2", "2-3" }, { "3-1", "3-2", "3-3" } };
String[] columnNames = { "column1", "column2", "column3" };
table = new JTable(cellData, columnNames);
return table;
}
private void setWaitCursor() {
Container container = getContentPane();
setWaitCursor(container);
}
private void setWaitCursor(Container container) {
for(int iCount = 0; iCount < container.getComponentCount(); iCount++) {
Component child = (Component) container.getComponent(iCount);
if(child instanceof Container) {
setWaitCursor((Container) child);
} else {
child.setCursor(new Cursor(Cursor.WAIT_CURSOR));
}
}
container.setCursor(new Cursor(Cursor.WAIT_CURSOR));
}
private void setDefaultCursor() {
Container container = getContentPane();
setDefaultCursor(container);
}
private void setDefaultCursor(Container container) {
for(int iCount = 0; iCount < container.getComponentCount(); iCount++) {
Component child = (Component) container.getComponent(iCount);
if(child instanceof Container) {
setDefaultCursor((Container) child);
} else {
child.setCursor(new Cursor(Cursor.DEFAULT_CURSOR));
}
}
container.setCursor(new Cursor(Cursor.DEFAULT_CURSOR));
}
public static void main(String[] argv) throws Exception {
ColumnResizeIconTest test = new ColumnResizeIconTest();
test.setVisible(true);
}
}
Click on the button a few times and try to resize the table column. The cursor is stuck with Default cursor.

As already mentioned in my comment: it's not entirely trivial to re-/set the cursors, not even for a single component :-) The base problem (in the recursive cursor setting to wait) is the assumption that all components do have the default cursor.
As you see on the table header, that assumption is not correct: on that component, the "default" is either the defaultCursor or the resizeCursor, depending on mouse location. Additionally, the internal cursor toggling is not very intelligent: it doesn't check for state (from the top of my head, was hit by that fact a while ago :-)
Not entirely sure what you want to reach, so don't have a concrete solution, except dropping the recursive setting entirely, it's too hard to get right. Options might be
make the glassPane (of the frame's rootpane) visible and set the waitCursor on it
use JLayer (jdk7) or JXLayer (jdk6) on a smaller area and set the waitCursor on that
use a less intrusive visualization, f.i. JProgressBar or a JXBusyLabel (in the SwingX project) somewhere
Addendum (for #mKorbel :-)
the problem is easily reproducible, with a little change to the OPs SSCCE (thanks for that!): change the addButton method as below, then click on the button and while the wait cursor is shown, move the mouse into the header and then to another column (across the column border). Doing so several times will lead to unpredicable cursors on the header ...
private void addButton() {
button = new JButton("Click Me");
final ActionListener off = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
setDefaultCursor();
button.setEnabled(true);
}
};
button.addActionListener( new ActionListener() {
public void actionPerformed(ActionEvent ae) {
setWaitCursor();
button.setEnabled(false);
Timer timer = new Timer(2000, off);
timer.setRepeats(false);
timer.start();
}
});
add(button, BorderLayout.NORTH);
}

1) you have redirect code
for(int i=0; i<2000; i++) {
System.out.print(i);
}
to the BackGround Task, you can implements javax.swing.Timer, SwingWorker, or wrap these code lines inside Runnable#Thread, example here
2) you have to restore Cursor on Error/Exception too, that's probably reason why Cursor wasn't changed

How to set JSplitPane-Divider collapse/expand State?

I have a JFrame with a JSplitPane that is OneTouchExpandable.
I want to remember the last Divider position of the JSplitPane on JFrame dispose and restore the Position if the JFrame is reopened.
It works well, but if the User expand one Side via the oneTouchExpandable UI-Widget then
I store only the 'int'-Position on dispose and set the 'int'-Position back again with the consequence on JFrame-resizing the JSplitPane-Divider jumps to the collapsed Component preferredSize.
How can I get/set the collapse/expand State?
EDIT
Now: the resize-Behavior is OK, but it is not exactly the same behavior like the first-time-open - cause now I have no MinimumDividerLocation. I wanted the SnapIn but further the collapsedState.
public class SplitPaneState {
public static void main( String[] args ) {
SwingUtilities.invokeLater( new Runnable() {
#Override
public void run() {
new SplitPaneState().createAndSowGUI();
}
});
}
private int position = -1;
private Dimension size = new Dimension( 500, 300 );
private void createAndSowGUI() {
final JFrame frame = new JFrame("frame");
frame.setSize( 200, 100 );
frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
frame.setLocationRelativeTo( null );
frame.getContentPane().add( new JButton( new AbstractAction(){
{
putValue( Action.NAME, "Open Dialog" );
}
#Override
public void actionPerformed( ActionEvent e ) {
final JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, new JLabel( "left Component" ), new JLabel( "right Component" ));
splitPane.setContinuousLayout( true );
splitPane.setOneTouchExpandable( true );
if(position != -1) {
boolean LeftIsCollapsed = position < splitPane.getMinimumDividerLocation();
if(LeftIsCollapsed) {
splitPane.getLeftComponent().setMinimumSize(new Dimension()); // fix by Martijn Courteaux
splitPane.setDividerLocation(0.0d); // fix by Martijn Courteaux
}else {
splitPane.setDividerLocation(position);
}
}
JDialog dialog = new JDialog(frame,"dialog"){
#Override
public void dispose() {
position = splitPane.getDividerLocation();
size = this.getSize();
super.dispose();
}
};
dialog.setSize( size );
dialog.setDefaultCloseOperation( JFrame.DISPOSE_ON_CLOSE );
dialog.setLocationRelativeTo( frame );
dialog.getContentPane().add( splitPane );
dialog.setVisible( true );
}
}
));
frame.setVisible( true );
}
}

I found that it is possible to collapse one side of the splitpane by setting the minimum size of the component to new Dimension() and then set the divider location:
// Hide left or top
pane.getLeftComponent().setMinimumSize(new Dimension());
pane.setDividerLocation(0.0d);
// Hide right or bottom
pane.getRightComponent().setMinimumSize(new Dimension());
pane.setDividerLocation(1.0d);
You can play with these settings to store and restore the collapse/expand state.

Forcing the divider position to a very small/large value to hide the top/bottom component works, but is defeated when the split pane gets resized, because of the component minimum size. Setting that size to 0 (as proposed in the accepted answer) works, but there are cases when you cannot/don't want to override that.
After looking into the BasicSplitPaneUI and associated classes, it turns out the "one touch expanding" buttons are calling BasicSPlitPaneUI.setKeepHidden(true), so the divider will stick to either end when resized.
Unfortunately, that method is package-private but setting the associated keepHidden field can be done using introspection, as shown in another answer:
sp.setDividerLocation(<0 or 999999>); // Divider is positioned at the top/bottom
Field m = BasicSplitPaneUI.class.getDeclaredField("keepHidden");
m.setAccessible(true);
m.set(sp.getUI(), true); // Divider position will stick

I improved version of toggle function:
/**
* toggle JSplitPane
* #param sp - splitpane to toggle
* #param upLeft - is it left or top component to collapse? or button or right
* #param collapse - true component should be collapsed
*/
public void toggle(JSplitPane sp, boolean upLeft, boolean collapse) {
try {
//get divider object
BasicSplitPaneDivider bspd = ((BasicSplitPaneUI) sp.getUI()).getDivider();
Field buttonField;
//get field button from divider
if (upLeft) {
if (collapse != (sp.getDividerLocation() < sp.getMinimumDividerLocation())) {
return;
}
buttonField = BasicSplitPaneDivider.class.getDeclaredField(collapse ? "rightButton" : "leftButton");
} else {
if (collapse != (sp.getDividerLocation() > sp.getMaximumDividerLocation())) {
return;
}
buttonField = BasicSplitPaneDivider.class.getDeclaredField(collapse ? "leftButton" : "rightButton");
}
//allow access
buttonField.setAccessible(true);
//get instance of button to click at
JButton button = (JButton) buttonField.get(((BasicSplitPaneUI) sp.getUI()).getDivider());
//click it
button.doClick();
//if you manage more dividers at same time before returning from event,
//you should update layout and ui, otherwise nothing happens on some dividers:
sp.updateUI();
sp.doLayout();
} catch (Exception e) {
e.printStackTrace();
}
}

Is hiding your dialog/frame an option?
// Create the dialog/frame which contains the JSplitPane
final JFrame frame = new JFrame("JSplitPane Problem");
frame.setCloseOperation(JFrame.HIDE_ON_CLOSE);
// ...
myButton.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
if (!frame.isVisible())
frame.setVisible(true);
}
});

http://docs.oracle.com/javase/7/docs/api/javax/swing/JSplitPane.html
void javax.swing.JSplitPane.setDividerLocation(double proportionalLocation)
Sets the divider location as a percentage of the
JSplitPane's size. This method is implemented in terms of
setDividerLocation(int). This method immediately changes the size of
the split pane based on its current size. If the split pane is not
correctly realized and on screen, this method will have no effect (new
divider location will become (current size * proportionalLocation)
which is 0).
So basically you need to have created your whole UI, called .pack() on the main JFrame
AND after that you can use JSplitPane.setDividerLocation(double). If you do it before UI layouting and all that stuff is done, the method will just do nothing as it states in the documentation and you already experienced.

JSplitPane has a method setDividerLocation(double), which sets the divider location as a percentage of the JSplitPane's size.
I tried to create similar functionality some time ago. I had the same problem. But even when I use the setDividerLocation(double) method, it didn't work properly. I believe that it's just JSplitPane bug.

public static void toggle(JSplitPane sp, boolean collapse) {
try {
BasicSplitPaneDivider bspd = ((BasicSplitPaneUI) sp.getUI()).getDivider();
Field buttonField = BasicSplitPaneDivider.class.
getDeclaredField(collapse ? "rightButton" : "leftButton");
buttonField.setAccessible(true);
JButton button = (JButton) buttonField.get(((BasicSplitPaneUI) sp.getUI()).getDivider());
button.getActionListeners()[0].actionPerformed(new ActionEvent(bspd, MouseEvent.MOUSE_CLICKED,
"bum"));
} catch (Exception e) {
e.printStackTrace();
}
}