Develop Reference

JSplitPane -- can't set maximum size;

Been a while since I've been here. I'm learning java and have a question as to why the panel I've created in a JSplitPane can be resized beyond the maximum that I've set:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class MainWindow {
//set all components
JFrame frame;
JPanel showPanel;//displays individual contact when clicked on in the contacts panel;
JPanel listPanel;// displays the contactsPanel
JSplitPane contactsSplitPane;
public void buildMainWindow() {// open method
frame = new JFrame("Contacts");
frame.setBackground(Color.WHITE);
frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
showPanel = new JPanel();
showPanel.setBackground(Color.WHITE);
listPanel = new JPanel();
listPanel.setBackground(Color.LIGHT_GRAY);
listPanel.setMaximumSize(new Dimension (300,1000));
//create SplitPane for the listPanel and showPanel
contactsSplitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, listPanel,showPanel);
contactsSplitPane.setOneTouchExpandable(true);
contactsSplitPane.setDividerLocation(50);
frame.setSize(1000, 1000);
frame.setVisible(true);
frame.add(BorderLayout.CENTER, contactsSplitPane);
}//close method
public static void main (String [] args) {
MainWindow MainWindow = new MainWindow ();
MainWindow.buildMainWindow();
}
}// close class
feel free to run and compile. I've set the size of the listPanel to a maximum of 300 pixels, but I can resize it way beyond that -- almost to the end of the frame. It's not possible to crate a single resizable pane, no?
Can someone let me know what I'm doing wrong? I'm obviously missing something, but I don't know what.

A JSplitPane doesn't respect the maximum size of either component.
However, it does respect the minimum size of a component.
So one approach could be do set the minimum size on the other component added to the split pane. You will need to override the getMinimumSize() method of this component since the size of the split pane can change dynamically.
Something like:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SplitPaneMaximum extends JPanel
{
JSplitPane splitPane;
public SplitPaneMaximum()
{
setLayout( new BorderLayout() );
JPanel red = new JPanel();
red.setBackground( Color.RED );
red.setPreferredSize( new Dimension(200, 100) );
red.setMinimumSize( new Dimension(100, 0) );
JPanel blue = new JPanel()
{
// Setting a minimum size here will limit the maximum size
// of the other component added to the split pane
#Override
public Dimension getMinimumSize()
{
int parentWidth = getParent().getSize().width;
Dimension d = getSize();
d.width = parentWidth - 200;
return d;
}
};
blue.setBackground( Color.BLUE );
blue.setPreferredSize( new Dimension(200, 100) );
splitPane = new JSplitPane();
splitPane.setLeftComponent( red );
splitPane.setRightComponent( blue );
splitPane.setResizeWeight(0.50);
add(splitPane, BorderLayout.CENTER);
}
private static void createAndShowUI()
{
JFrame frame = new JFrame("SplitPaneMaximum");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add( new SplitPaneMaximum() );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible( true );
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowUI();
}
});
}
}
Now the width of the red panel can only be sized between 100 and 200 pixels.

How would I position a JComponent to true center in a BorderLayout?

I am developing a Swing application using BorderLayout to position the components. Since BorderLayout.CENTER positions components to whatever is left after the other components are placed, and that fact is making my GUI look weird, I was wondering if there was a way to position components to true center, rather than in between the two sides. Since BorderLayout spaces make a component fill an entire space, I'm guessing the solution would be to wrap the component into a JPanel. However, positioning the component to the center of this panel will make the component be closer to one side than another if you have components on other sides. How do I work around this?
These images demonstrate the problem and the ideal solution; the gray border represents the BorderLayout.SOUTH (wrapped in a JPanel) of the main frame. The black squares represents components that are throwing the center component off. The red square represents the component that needs to be centered.
Problem:
Ideal solution:

As I see the problem, in order for the red component to be centered the right and left components must be of equal size.
You might be able to use the Relative Layout.
The RelativeLayout will allow you to make the right/left components the same size while keeping the center component at its preferred size. As the frame is resized space will be added/removed from the right/left components.
For example:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class SSCCE extends JPanel
{
public SSCCE()
{
JPanel left = new JPanel( new FlowLayout(FlowLayout.LEFT) );
JPanel leftBox = new JPanel();
leftBox.setPreferredSize( new Dimension(200, 50) );
leftBox.setBackground( Color.BLACK );
left.add( leftBox );
JPanel center = new JPanel( new FlowLayout(FlowLayout.CENTER) );
JPanel centerBox = new JPanel();
centerBox.setPreferredSize( new Dimension(50, 50) );
centerBox.setBackground( Color.RED );
center.add( centerBox );
JPanel right = new JPanel( new FlowLayout(FlowLayout.RIGHT) );
JPanel rightBox = new JPanel();
rightBox.setPreferredSize( new Dimension(50, 50) );
rightBox.setBackground( Color.BLACK );
right.add( rightBox );
setLayout( new RelativeLayout(RelativeLayout.X_AXIS, 5) );
add(left, new Float(1));
add(center);
add(right, new Float(1));
}
private static void createAndShowGUI()
{
JFrame frame = new JFrame("SSCCE");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new SSCCE());
frame.setLocationByPlatform( true );
frame.pack();
frame.setVisible( true );
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowGUI();
}
});
}
}
The one problem with the relative layout is that when you pack the frame the components will be dislayed too small since the preferred size is simply the sum of the components. So the left panel will be truncated.
In the example above you can add the following to get around this problem:
right.add( rightBox );
right.setPreferredSize( left.getPreferredSize() ); // added
Another option might be to use the OverlayLayout which can be set up to display the red panel over top of a panel containing the two other components:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class SSCCE extends JPanel
{
public SSCCE()
{
JPanel left = new JPanel( new FlowLayout(FlowLayout.LEFT) );
JPanel leftBox = new JPanel();
leftBox.setPreferredSize( new Dimension(200, 50) );
leftBox.setBackground( Color.BLACK );
left.add( leftBox );
JPanel center = new JPanel( new FlowLayout(FlowLayout.CENTER) );
center.setOpaque(false);
JPanel centerBox = new JPanel();
centerBox.setPreferredSize( new Dimension(50, 50) );
centerBox.setBackground( Color.RED );
center.add( centerBox );
JPanel right = new JPanel( new FlowLayout(FlowLayout.RIGHT) );
JPanel rightBox = new JPanel();
rightBox.setPreferredSize( new Dimension(50, 50) );
rightBox.setBackground( Color.BLACK );
right.add( rightBox );
JPanel main = new JPanel( new BorderLayout() );
main.add(left, BorderLayout.LINE_START);
main.add(right, BorderLayout.LINE_END);
setLayout( new OverlayLayout(this) );
add(center);
add(main);
}
private static void createAndShowGUI()
{
JFrame frame = new JFrame("SSCCE");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new SSCCE());
frame.setLocationByPlatform( true );
frame.pack();
frame.setVisible( true );
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowGUI();
}
});
}
}

JScrollPane doesn't show scroll bars when JPanel is added

I'm tried to add a JPanel to a JScrollPane using:
panel1 Panel1 = new panel1();
jScrollPane1.setViewportView(Panel1);
and it worked. But the problem is scrollPane doesn't show scroll bars even the Panel1 is bigger. (I'm working with NetBeans & panel1 is a jpanel form)

Override, getPreferredSize() method for the said JScrollPane, you might be able to see the Scroll Bar. Or one can simply call setPreferredSize(), though as stated in the API
Sets the preferred size of this component. If preferredSize is null, the UI will be asked for the preferred size
overriding will be beneficial, as it tends to define some appropriate dimensions to the said JComponent.
Something like this:
JScrollPane scroller = new JScrollPane() {
#Override
public Dimension getPreferredSize() {
return new Dimension(300, 200);
}
};
scroller.setViewportView(panelWithScroll);
One example:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class PanelScroller {
private void displayGUI() {
JFrame frame = new JFrame("Swing Worker Example");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
JPanel contentPane = new JPanel();
JPanel panelWithScroll = new JPanel();
panelWithScroll.setLayout(new GridLayout(0, 1, 5, 5));
JScrollPane scroller = new JScrollPane() {
#Override
public Dimension getPreferredSize() {
return new Dimension(300, 200);
}
};
scroller.setViewportView(panelWithScroll);
//scroller.setPreferredSize(new Dimension(300, 200));
for (int i = 0; i < 20; i++) {
panelWithScroll.add(new JLabel(Integer.toString(i + 1), JLabel.CENTER));
}
contentPane.add(scroller);
frame.setContentPane(contentPane);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
Runnable runnable = new Runnable() {
#Override
public void run() {
new PanelScroller().displayGUI();
}
};
EventQueue.invokeLater(runnable);
}
}

If you only want the scrollbars to show up you can call
JScrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
JScrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
But that don't make them work at all.
if you wont to make them work you can try to set the preferred size of the component inside the Scrollpane to larger then size of Scrollpane and then call repaint(e.g. by make the window fullscreen)

Centering Panel in Java

For some reason i am having problems centering my panel vertically that is located inside another panel. I do exactly as the examples i studied but still no luck.
Down there is my code. Despite using setAlignmentY(0.5f) on my container panel, it still wont center when i resize the window.
Also the components inside container panel wont center either, despite setAligenmentX(0.5f).
I wonder if there is a solution for this, I pretty much tried everything out there but couldnt find a solution.
JLabel idLabel;
JLabel passLabel;
JTextField id;
JTextField pass;
JButton enter;
JPanel container;
public JournalLogin()
{
//setLayout(new FlowLayout());
//setPreferredSize(new Dimension(500, 500));
//setBorder(BorderFactory.createEmptyBorder(100, 100, 100, 100));
container = new JPanel();
container.setLayout(new MigLayout());
container.setAlignmentX(0.5f);
container.setAlignmentY(0.5f);
container.setPreferredSize(new Dimension(300, 300));
container.setBorder(BorderFactory.createTitledBorder("Login"));
add(container);
idLabel = new JLabel("ID:");
idLabel.setAlignmentX(0.5f);
container.add(idLabel);
id = new JTextField();
id.setText("id");
id.setAlignmentX(0.5f);
id.setPreferredSize(new Dimension(80, 20));
container.add(id, "wrap");

setAlignmentX and Y are not the way to go about doing this. One way to center a component in a container is to have the container use GridBagLayout and to add the component without using any GridBagConstraints, a so-called default addition. There are other ways as well.
For example to alter Nick Rippe's example (1+ to him):
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import javax.swing.*;
public class UpdatePane2 extends JPanel {
private static final int PREF_W = 300;
private static final int PREF_H = 200;
public UpdatePane2() {
JPanel innerPanel = new JPanel();
innerPanel.setLayout(new BorderLayout());
innerPanel.add(new JLabel("Hi Mom", SwingConstants.CENTER),
BorderLayout.NORTH);
innerPanel.add(new JButton("Click Me"), BorderLayout.CENTER);
setLayout(new GridBagLayout());
add(innerPanel);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private static void createAndShowGui() {
JFrame frame = new JFrame("UpdatePane2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new UpdatePane2());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Alignments tend to be pretty picky in Swing - they do [usually] work... but if all you're looking for is a panel that's centered, I'd recommend using Boxes in the BoxLayout (My personal favorite LayoutManager). Here's an example to get you started:
import java.awt.Dimension;
import javax.swing.*;
public class UpdatePane extends JPanel{
public static void main(String... args) {
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run() {
//Create Buffers
Box verticalBuffer = Box.createVerticalBox();
Box horizontalBuffer = Box.createHorizontalBox();
verticalBuffer.add(Box.createVerticalGlue()); //Top vertical buffer
verticalBuffer.add(horizontalBuffer);
horizontalBuffer.add(Box.createHorizontalGlue()); //Left horizontal buffer
//Add all your content here
Box mainContent = Box.createVerticalBox();
mainContent.add(new JLabel("Hi Mom!"));
mainContent.add(new JButton("Click me"));
horizontalBuffer.add(mainContent);
horizontalBuffer.add(Box.createHorizontalGlue()); //Right horizontal buffer
verticalBuffer.add(Box.createVerticalGlue()); //Bottom vertical buffer
// Other stuff for making the GUI
verticalBuffer.setPreferredSize(new Dimension(300,200));
JFrame frame = new JFrame();
frame.add(verticalBuffer);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
});
}
}

You will need to get the LayoutManager to center the layout for you. Currently it looks like the implementation of "MigLayout" does not honor the Alignment. Try changing it or creating a subclass.

SetVisible(false) changes the layout of my components within my Panel

How do I make the subpanels within my main panel stay where they are when I set one of the subpanels to be invisible?
What I have looks like:
[ (Panel1) (Panel2) (Panel3) (Panel4) ]
When I do panel3.setVisible(false) it then looks like:
[ (Panel1) (Panel2) (Panel4) ]
I would like it to look like:
[ (Panel1) (Panel2) (Panel4) ]
I am using the GridBagLayout and my mainPanel declaration looks like:
final JPanel panel = new JPanel(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
and I add an new panel like:
final JTextField valueTextField = new JTextField();
valueTextField.setPreferredSize(new Dimension(80, 25));
valueTextField.setName("Value");
c.gridx =0;
panel.add(valueTextField, c);
I'll provide more code if needed and I don't care which layout I use as long as it gets me what I want.

I suggest using a CardLayout within the individual cells, and instead of setting it to invisible, switch to an empty panel instead.
The code below demonstrates this. Within hidePanel() there are two options to hide the cell with the CardLayout route currently enabled.
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class InvisiblePanels {
public static void main(String... args) throws Exception {
JFrame frame = new JFrame();
frame.setLayout(new GridBagLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
GridBagConstraints c = new GridBagConstraints();
c.gridx = 0;
frame.add(new MyPanel(), c);
c.gridx = 1;
frame.add(new MyPanel(), c);
c.gridx = 2;
frame.add(new MyPanel(), c);
frame.pack();
frame.setVisible(true);
}
private static class MyPanel extends JPanel {
CardLayout layout;
public MyPanel() {
layout = new CardLayout();
setLayout(layout);
JButton button = new JButton("Click me");
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
hidePanel();
}
});
add(button, "visible");
add(new JPanel(), "invisible");
layout.show(this, "visible");
}
public void hidePanel() {
// setVisible(false);
layout.show(this, "invisible");
}
}
}

I believe all the layout manager respect the visibility of a component and don't include invisible components in the preferred size and layout calculations.
One solution might be to wrap all your panels in a panel using the OverlayLayout:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class OverlayLayoutInvisible
{
public static void main(String[] args)
{
JPanel panel = new JPanel();
panel.add( createPanel("Button 1") );
panel.add( createPanel("Button 2") );
panel.add( createPanel("Button 3") );
panel.add( createPanel("Button 4") );
panel.add( createPanel("Button 5") );
JFrame frame = new JFrame();
frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
frame.add( panel );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
public static JPanel createPanel(String text)
{
JButton button = new JButton( text );
button.addActionListener( new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
Component c = (Component)e.getSource();
c.setVisible(false);
}
});
InvisibleComponent ic = new InvisibleComponent( button );
JPanel panel = new JPanel();
panel.setLayout( new OverlayLayout(panel) );
panel.add( ic );
panel.add( button );
return panel;
}
public static class InvisibleComponent extends JComponent
{
private Component master;
public InvisibleComponent(Component master)
{
this.master = master;
setAlignmentX( master.getAlignmentX() );
setAlignmentY( master.getAlignmentY() );
}
public Dimension getPreferredSize()
{
return master.getPreferredSize();
}
}
}

You might be able to tweak GridLayout (do you have an SSCCE?)
Otherwise:
Put Panel3 and Panel4 together in a single panel that you add to the GridBagLayout. Then setup the new Panel in a Layout like FlowLayout (aligned Left with a preferred size), BorderLayout, GridLayout, etc.