Develop Reference

JList resize after add element

I have a little problem with size of a JList:
There is a JFrame with three JLists(each in JScrollPane). You can add an item to list by click on it. After program start all JLists have the same width. But after populate any list is his width reduced and created space is added to empty list equally.
I want to stop this resizing. I hope that the code below will describe my problem better.
package test;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.DefaultListModel;
import javax.swing.GroupLayout;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
public class Test extends JFrame {
public Test() {
GroupLayout layout = new GroupLayout(this.getContentPane());
this.setLayout(layout);
JList listA = new JList(new DefaultListModel<String>());
JList listB = new JList(new DefaultListModel<String>());
JList listC = new JList(new DefaultListModel<String>());
MouseListener listener = new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
((DefaultListModel) ((JList) e.getSource()).getModel()).addElement("some text");
revalidate();
}
};
listA.addMouseListener(listener);
JScrollPane paneA = new JScrollPane(listA);
listB.addMouseListener(listener);
JScrollPane paneB = new JScrollPane(listB);
listC.addMouseListener(listener);
JScrollPane paneC = new JScrollPane(listC);
layout.setAutoCreateGaps(true);
layout.setAutoCreateContainerGaps(true);
layout.setHorizontalGroup(layout.createSequentialGroup().addComponent(paneA).addComponent(paneB).addComponent(paneC));
layout.setVerticalGroup(layout.createSequentialGroup().addGroup(layout.createParallelGroup(GroupLayout.Alignment.CENTER).addComponent(paneA).addComponent(paneB).addComponent(paneC)));
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.pack();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
Test test = new Test();
test.setVisible(true);
}
});
}
}

To make your components to be of constant size you will need to use addComponent(Component component, int min, int pref, int max). So just replace your code with this
layout.setHorizontalGroup(layout.createSequentialGroup()
.addComponent(paneA, GroupLayout.PREFERRED_SIZE, 200, GroupLayout.PREFERRED_SIZE)
.addComponent(paneB, GroupLayout.PREFERRED_SIZE, 200, GroupLayout.PREFERRED_SIZE)
.addComponent(paneC, GroupLayout.PREFERRED_SIZE, 200, GroupLayout.PREFERRED_SIZE));
instead of this
layout.setHorizontalGroup(layout.createSequentialGroup().addComponent(paneA).addComponent(paneB).addComponent(paneC));
Here I have used properties of GroupLayout and a constant width 200 to make it stable.

The JLists are likely been resized because of the size of the values been rendered are smaller than they were when they were first created. They are then be re-laid out by the layout manager to meet these new requirements.
There is a complicated amount of work going on between the JScrollPane, the JViewport, the JList and the JLists ListCellRenderer in which you don't want to get involved.
Instead, you want to provide "hints" to the JLists about how you want them to be sized.
For example...
You could use JList#setPrototypeCellValue to provide the JList with informaiton about the maximum size of the value that would be added to the list in the future. This is especially handy when you have a large number of values to add, as the JList won't need to check each one to determine the height of each row and the width required to accommodate the values.
The drawback is, you will need to know the maximum width of any of the values are likely to add...
Alternatively, you could use a LayoutManager which gives you more control over how components should be positioned and changed, such as GridBagLayout or even MigLayout
You should also check out Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?

Here is one way to fix the issue.
JScrollPane paneA = new JScrollPane(listA);
paneA.setPreferredSize(new Dimension(paneA.getPreferredSize().height, 300));
listB.addMouseListener(listener);
JScrollPane paneB = new JScrollPane(listB);
paneB.setPreferredSize(new Dimension(paneB.getPreferredSize().height, 300));
listC.addMouseListener(listener);
JScrollPane paneC = new JScrollPane(listC);
paneC.setPreferredSize(new Dimension(paneC.getPreferredSize().height, 300));
I am not familiar with the GroupLayout manager. The following document might provide a way to control the layout further. http://docs.oracle.com/javase/tutorial/uiswing/layout/group.html (See Component Size and Resizability)

Two Components on top of each other using MigLayout

I'm trying to get two components,
frame.getContentPane().setLayout(new MigLayout("", "[53px,grow][57px][grow]", "[23px][][][]"));
JTextPane itemTitle = new JTextPane();
frame.getContentPane().add(itemTitle,"cell 0 4,alignx left,aligny top");
itemTitle.setVisible(true);
itemTitle.setMinimumSize(new Dimension(50, 50));
List choices = new List();
frame.add(choices, "cell 0 4,alignx left,aligny top");
choices.setVisible(true);
to be in the same place, but all the happens is this:
The two components highlighted at itemTitle and choices.
My aim is to have the buttons above set one "setVisible" to true and the other to false. They would never both be true. How can I get two components in one cell at the same time? It also puts my above buttons out of place and I'm not too sure why. I put above the important code referring to the two components, I could put the full GUI code if you requested.
I found this: Fill Entire Cell With Two Components Using MigLayout However it is over years old and to be honest, I don't understand the solution.
I'm sort of learning as I go, I've never used MigLayout before. Should I be using a different layout?
Thanks for any help

to be in the same place... My aim is to have the buttons above set one "setVisible" to true and the other to false. They would never both be true
Then you should be using a JPanel that contains those two components. Then you use a Card Layout on that panel and use the CardLayout to determine which component is visible at any given time. This panel can be added to the panel using the MigLayout just like any other component.
List choices = new List();
Looks to me like you are using an AWT component. You should be using JList for a Swing application.

Should I be using a different layout?
No, stick with MigLayout. You have chosen the right layout manager.
I advice you to invest some time into learning this manager; create couple
of smaller practical examples, learn the numerous constraints that this
manager provides.
It also puts my above buttons out of place and I'm not too sure why.
MigLayout is a grid-based layout manager. (Its most important mode is.)
The gap between the New and Open buttons is created because the
highlighted components and the New button form a column. The column width
is determined by the width of the largest cell. To bypass this, we can
use the split constraint. (Often used in combination with span constraint.)
In my example I use this technique to center two buttons above the
currently visible label.
If we are not sure about something in the layout, we can use the
debug layout constraint which paints the lines of the grid and bounds
of the components.
frame.getContentPane().setLayout(new MigLayout("", "[53px,grow][57px][grow]", "[23px][][][]"));
Do not set bounds in pixels. You are not utilizing of one of the
most important advantages of this manager -- independence of resolution and
DPI. Bounds in pixels are not portable. A 3px gap between buttons looks OK on a smaller screen but is not acceptable on a larger one.
MigLayout provides several options to choose from including related and unrelated gaps, logical pixels, points, or centimeters.
itemTitle.setMinimumSize(new Dimension(50, 50));
Setting a minimum size of a component is usually not necessary. But if we need to
do it, we have the wmin and wmax constraints. This should be done by the
layout manager, not by code outside of it. The set(Minimum|Maximum|Preferred)size
methods should be avoided. (With poorer managers, one cannot do without them, however.)
And again, setting dimensions in pixels is not optimal.
Now we get to the solution. MigLayout has hidemode constraint to deal
with your requirement. There are four hide modes. I assume that we need
the hidemode 3, in which all invisible components do not participate in the
layout.
package com.zetcode;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.util.ArrayList;
import javax.swing.AbstractAction;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import net.miginfocom.swing.MigLayout;
public class HidingComponentsEx extends JFrame {
private ArrayList<JLabel> lbls;
private int itemVisible = 0;
public HidingComponentsEx() {
initUI();
}
private void initUI() {
createLabels();
JButton prevBtn = new JButton("Previous");
prevBtn.addActionListener(new PrevAction());
JButton nextBtn = new JButton("Next");
nextBtn.addActionListener(new NextAction());
JPanel pnl = new JPanel(new MigLayout("ins dialog"));
pnl.add(prevBtn, "split 2, center");
pnl.add(nextBtn, "wrap");
for (JLabel lbl : lbls) {
pnl.add(lbl, "cell 0 1, w 250lp, h 100lp, hidemode 3");
}
add(pnl);
pack();
setTitle("MigLayout example");
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private void createLabels() {
lbls = new ArrayList<>();
lbls.add(createLabel("North Sea"));
lbls.add(createLabel("Ionian Sea"));
lbls.add(createLabel("Norwegian Sea"));
lbls.add(createLabel("Bering Sea"));
lbls.add(createLabel("Dead Sea"));
lbls.get(itemVisible).setVisible(true);
}
private class NextAction extends AbstractAction {
#Override
public void actionPerformed(ActionEvent e) {
lbls.get(itemVisible).setVisible(false);
itemVisible++;
if (itemVisible > 4) {
itemVisible = 0;
}
lbls.get(itemVisible).setVisible(true);
}
}
private class PrevAction extends AbstractAction {
#Override
public void actionPerformed(ActionEvent e) {
lbls.get(itemVisible).setVisible(false);
itemVisible--;
if (itemVisible < 0) {
itemVisible = 4;
}
lbls.get(itemVisible).setVisible(true);
}
}
private JLabel createLabel(String text) {
JLabel lbl = new JLabel(text, JLabel.CENTER);
lbl.setVisible(false);
lbl.setBorder(BorderFactory.createEtchedBorder());
return lbl;
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
HidingComponentsEx ex = new HidingComponentsEx();
ex.setVisible(true);
}
});
}
}
Our example has two buttons and five labels. The buttons dynamically change their
visibility.

Can this Java GUI can be simplified?

I'm writing a Java GUI application, and is something like this:
JPanel main = new JPanel(new GridLayout(1, 1));
JPanel buttonPanel = new JPanel();
buttonPanel.add(button);
main.add(buttonPanel)
I want to add a button to the grid, but i want it centered on the grid panel.
Adding the button to another JPanel allows me to center it to the Grid.
Is there any shorter way to do this?
For example:
JPanel main = new JPanel(new GridLayout(1, 1));
JPanel buttonPanel = JPanel();
main.add(new JPanel().add(button));
This is not working for me.
Thanks :)

I agree with the other commenters that reducing the number of lines of code probably isn't as neccessary as you think it is: Generally speaking, your goal should be to reduce code complexity, not code length, and efforts to minimize length often lead to code that is more complex/hard to understand rather than less.
That said, applying basic OO principles can enable you to shorten your code while maintaining (if not increasing) its clarity:
class CenteredContentPanel extends JPanel {
CenteredContentPanel(JComponent addTo){
this.setLayout(new GridLayout(1,1));
JPanel parentPanel = new JPanel();
parentPanel.add(addTo);
this.add(parentPanel);
}
}
Now, you can add as many of these as you please to a parent container with a single line of code:
JPanel main = new JPanel();
main.add(new CenteredContentPanel(button));
//repeat above line to add as many "centered" components as you need to
(code is untested, as I don't have access to an IDE at the moment, but you get the gist...)

You need to add main to the frame:
add(main.add(new JPanel().add(button)));
This works fine for me:
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MyFrameClass extends JFrame
{
public MyFrameClass(){
JPanel main = new JPanel(new GridLayout(1, 1));
JButton button = new JButton();
add(main.add(new JPanel().add(button)));
setSize(800,600);
setVisible(true);
}
public static void main (String [] args)
{
new MyFrameClass();
}
}

Java Swing simple center of JPanel in other JPanel

I have this incredibly easy task of wanting a nice centered JPanel inside another JPanel. The parent is set to 900, 550, and the child should be approximately 200,400 or so.
To do this, I thought giving the parent a BorderLayout and then setting the setPreferredSize(200, 400) of the child. This child would be in the CENTER. Two empty JPanels would be on the EAST and WEST. Of course this did not work. Giving the two sidepanels a setPreferredSize() of course DID work. Problem with this is that narrowing the Frame causes the center pane to go away.
Here's some sample code that should give show the issue:
import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Component;
import java.awt.Dimension;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Temporary {
public static Temporary myObj = null;
private JFrame mainFrame;
public void go(){
mainFrame = new JFrame("Swing");
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.setPreferredSize(new Dimension(900,550));
JPanel mainCards = new JPanel(new CardLayout());
mainCards.add(loginLayer(), "Login");
mainFrame.setContentPane(mainCards);
mainFrame.pack();
mainFrame.setLocationRelativeTo(null);
mainFrame.setVisible(true);
}
public JPanel loginLayer(){
JPanel masterPane = new JPanel(new BorderLayout());
JPanel centerPane = new JPanel();
centerPane.setLayout(new BoxLayout(centerPane, BoxLayout.Y_AXIS));
centerPane.setPreferredSize(new Dimension(100,200));
JLabel label = new JLabel("Swing is overly");
label.setAlignmentX(Component.CENTER_ALIGNMENT);
centerPane.add(label);
JButton button = new JButton("complicated");
button.setAlignmentX(Component.CENTER_ALIGNMENT);
centerPane.add(button);
JTextField textField = new JTextField(10);
centerPane.add(textField);
JPanel filler = new JPanel();
JPanel filler2 = new JPanel();
masterPane.add(filler, BorderLayout.WEST);
masterPane.add(centerPane, BorderLayout.CENTER);
masterPane.add(filler2, BorderLayout.EAST);
return masterPane;
}
public static void main(String[] args){
myObj = new Temporary();
myObj.go();
}
}

BorderLayout will, by it's nature, give as much of the available space as it can to the CENTER component. This is how it's designed.
If you want the component to be centered within the parent container, BUT maintain it's preferred size, you should consider using a GridBagLayout instead. Without any additional constraints, this should achieve the result you're after
For example...
public JPanel loginLayer(){
JPanel masterPane = new JPanel(new GridBagLayout);
JPanel centerPane = new JPanel();
centerPane.setLayout(new BoxLayout(centerPane, BoxLayout.Y_AXIS));
JLabel label = new JLabel("Swing is overly");
label.setAlignmentX(Component.CENTER_ALIGNMENT);
centerPane.add(label);
JButton button = new JButton("complicated");
button.setAlignmentX(Component.CENTER_ALIGNMENT);
centerPane.add(button);
JTextField textField = new JTextField(10);
centerPane.add(textField);
masterPane.add(centerPane);
// Add additional borders to providing padding around the center pane
// as you need
return masterPane;
}
I would also avoid actively setting the preferred size of component in this way, as it's possible that the components you're adding to it will exceed your expectations, instead, make use of things like EmptyBorder (for example) to add additional white space arouond the component and it's contents

In Java Swing, you generally want to avoid creating a bunch of statically positioned items with preferred sizes and absolute positions, because things get weird with resizing (as you've noticed). Instead you want to rely on the fluid LayoutManagers. There is an excellent tutorial here. Or, if you want to supply a mock-up of some sort to show the actual UI you are trying to create, I could provide some more feedback.

NetBeans, GUI builder (group layout) centering a component

I'm trying to design a JButton (an "Ok" button) that to look good has to be horizontally centered in the containing JFrame.
I'm using the GUI Builder with the Free Form layout (GroupLayout).
I've taken several GUI builder tutorials (http://netbeans.org/kb/docs/java/quickstart-gui.html) but haven't found this topic. In other gui builders (delphi) this can be done by removing the anchors from both edges.

GroupLayout does support centering of components. It is a very capable
layout manager. I personally put it after the MigLayout manager and before
the FormLayout manager.
In the following three examples, we have a panel and a button. The button
is horizontally centered.
Centering with NetBeans Builder
To center a component using a Netbeans Builder, we need to create
horizontal resizable gaps from both sides of the button.
The green area of the screenshot is a currently selected gaps. The strings
inside the gaps suggest that it is a resizable gap.
The gaps are automatically added when we place components on the form.
To define a gap to be resizable, we right click on the gap and select
the "Edit Layout Space" option. We get the following dialog:
To get a resizable gap, we check the Resizable check box.
Centering manually by using a parallel group
Components can be centered in the parallel group by passing
the GroupLayout.Alignment.CENTER parameter.
package com.zetcode;
import java.awt.Container;
import java.awt.EventQueue;
import javax.swing.BorderFactory;
import javax.swing.GroupLayout;
import static javax.swing.GroupLayout.Alignment.CENTER;
import static javax.swing.GroupLayout.DEFAULT_SIZE;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class GroupLayoutCenter extends JFrame {
public GroupLayoutCenter() {
initUI();
setTitle("Centered button");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
}
private void initUI() {
Container pane = getContentPane();
GroupLayout gl = new GroupLayout(pane);
pane.setLayout(gl);
gl.setAutoCreateGaps(true);
gl.setAutoCreateContainerGaps(true);
JPanel pnl = new JPanel();
pnl.setBorder(BorderFactory.createEtchedBorder());
JButton btn = new JButton("Button");
gl.setHorizontalGroup(gl.createParallelGroup(CENTER)
.addComponent(pnl, DEFAULT_SIZE, 200, DEFAULT_SIZE)
.addComponent(btn)
);
gl.setVerticalGroup(gl.createSequentialGroup()
.addComponent(pnl, DEFAULT_SIZE, 200, DEFAULT_SIZE)
.addComponent(btn)
);
pack();
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
GroupLayoutCenter ex = new GroupLayoutCenter();
ex.setVisible(true);
}
});
}
}
Centering manually by using gaps
This solution is what NetBeans generated code does. We place
two resizable gaps to the left and right sides of the button.
package com.zetcode;
import java.awt.Container;
import java.awt.EventQueue;
import javax.swing.BorderFactory;
import javax.swing.GroupLayout;
import static javax.swing.GroupLayout.DEFAULT_SIZE;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class GroupLayoutCenter2 extends JFrame {
public GroupLayoutCenter2() {
initUI();
setTitle("Centered button");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
}
private void initUI() {
Container pane = getContentPane();
GroupLayout gl = new GroupLayout(pane);
pane.setLayout(gl);
gl.setAutoCreateGaps(true);
gl.setAutoCreateContainerGaps(true);
JPanel pnl = new JPanel();
pnl.setBorder(BorderFactory.createEtchedBorder());
JButton btn = new JButton("Button");
gl.setHorizontalGroup(gl.createParallelGroup()
.addComponent(pnl, DEFAULT_SIZE, 200, DEFAULT_SIZE)
.addGroup(gl.createSequentialGroup()
.addGap(5, 100, Short.MAX_VALUE)
.addComponent(btn)
.addGap(5, 100, Short.MAX_VALUE))
);
gl.setVerticalGroup(gl.createSequentialGroup()
.addComponent(pnl, DEFAULT_SIZE, 200, DEFAULT_SIZE)
.addComponent(btn)
);
pack();
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
GroupLayoutCenter2 ex = new GroupLayoutCenter2();
ex.setVisible(true);
}
});
}
}

If you want your component to remain centered in its container if the container is resized, you have several options available to you, but I don't think that GroupLayout is one of them (please correct me if I'm wrong). One way is to change the container's layout to GridBagLayout, and then simply add the JButton into it without any constraints.

Try GridbagLayout See this

Try another LayoutManager!
GroupLayout is very obscure when just looking at the code generated by NetBeans.
If you used DesignGridLayout then what you need is as simple as:
DesignGridLayout layout = new DesignGridLayout(container);
layout.row().center().add(okButton);

javax.swing.Box.Filler can be used to pad space around a component inside a GroupLayout. In NetBeans Matisse (GUI Builder) they're called 'Horizontal Strut' under the 'Swing Fillers' section of the palette. Just put one on either side of your button, size them to fill all the empty space between the button and the edge of the container, and make sure they're both flagged to Auto Resize Horizontally.
As for using another LayoutManager, I know people don't like GroupLayout because it is not conducive to manual coding. That is by design. As the docs say, GroupLayout is intended to be used by GUI builders. So as long as you're ok with tying yourself to using NetBeans & Matisse for the life of your GUI, GroupLayout is really the best option.