Develop Reference

Refreshing JLabel - Java

I have some problems with JLabels and Frames..
I have the following code:
list.addListSelectionListener(
new ListSelectionListener() {
#Override
public void valueChanged(ListSelectionEvent e) {
//System.out.println(e.getFirstIndex());
String selectedFile = list.getSelectedValue().toString();
System.out.println("Selected file " + selectedFile);
JLabel label;
ImageIcon icon = new ImageIcon("C:\\Users\\danie\\Pictures\\" + selectedFile);
// frame.setSize(1047, 680);
label = new JLabel(icon);
//label.setSize(100,100);
frame.getContentPane().add(label, BorderLayout.CENTER);
frame.revalidate();
frame.repaint();
}
});
I want to refresh the label in the center of the borderlayout if a item in a JList is selected. But with this code, the old image is futher displayed and the new image is only drawed behind the existing image.
Could anyone help me? :)

First you are creating a new JLabel instance instead of working on the existing one. What you actually want to do is:
labe.setIcon(icon);
This will automatically refresh the element.

Suggestions:
Don't create a new JLabel, give it an ImageIcon and expect the existing JLabel to change. The two JLabels, the original one and the one created here, are two completely different objects, and changing the state of one (the icon it's displaying) will not magically change the state of the other.
Do make sure that the original JLabel has an instance variable in the class (not in your listener class), a field, refer to it, and then in your listener code, change the icon displayed in that JLabel by calling its setIcon(...) method
No need to call revalidate() or repaint() here as this should be done if you change components held within a container, such as if you removed the original JLabel from the JFrame's contentPane and swapped in a new one. Note that I do not recommend that you do this as it is over-complicating what should be a simple thing -- swapping icons.
To simplify things, I suggest that you read all your images in at program startup, create ImageIcons at that time, and then put them into an array or collection (such as an ArrayList<Icon> or a HashMap<String, Icon>), and then in your listener code, extract the correct icon, and put it into the existing JLabel.

You are not using the same JLabel it seems. You should alter the label you already have, not create a new one.

Advice: Java GUI Using JFrame

I Have created a form and designed it using Swing Components. It is linked to MySQL, so i have few buttons, like Submit (Which When Clicked validates and updates the database). But I also have buttons to view and edit database. When clicked i have worked on Delete Record using JOptionPane (YES_NO_OPTION etc), but when it comes to editing, i want to put Combo boxes and Text Fields etc, which might not be preferred in JOptionPane. Creating a new Window would help, but is there any other easier Default Classes like JOptionPane in which i can use Many components? Also to display Database records?

I believe what you are looking for are JDialogs, these are the "small" popup windows you are looking for. You may add any swing component you wish to it.
Here is an example of creating one and adding a JTextField to it.
JDialog popup = new JDialog();
//Set window title
popup.setTitle("Example");
//Set window size
popup.setWindowSize(300, 200);
//Force window to stay on top till exit
popup.setModal(true);
//Create and add a JTextField
JTextField input = new JTextField();
popup.add(input);
popup.setVisable(true);

Java Swing: Add a component by code in NetBeans

I'm using NetBeans, and I've a JFrame where I added a JPanel to it using the NetBeans's palette.
I want to add a JRadioButton manually to that JPanel, so this is the code I tried in the constructor :
ButtonGroup group = new ButtonGroup();
JRadioButton btn1 = new JRadioButton("btn1 ");
JPanel1.add(btn1);
But when I run that JFrame I don't see that JRadioButton anywhere, but it works when I add it using the NetBens's palette.
How can I solve this problem ?

Make sure that the JPanel is not using GroupLayout. Most any other layout would work well, but likely for the moment, JPanel's default FlowLayout will work best.
Be sure to call revalidate() and repaint() on the JPanel after adding a component, if you are adding the component after the GUI has been rendered, such as on a button push.
If still having problems, show your code.
General advice: avoid using code generation utilities until after you understand the underpinnings of the GUI library, here Swing. You won't regret doing this.

The problem with NetBeans GUI Builder is that it initializes everything for you, where you can't alter the code unless you open the file on some other platform. In which case you have the risk of totally messing up the code.
What I can suggest is to maybe attempt something like this
Create an empty JPanel with a preferred size that you set in the property pane. You may also want to set the layout also, depending on your requirements.
After the initComponent() then add the JRadioButtons
public MyGUI(){
initComponents();
ButtonGroup group = new ButtonGroup();
JRadioButton btn1 = new JRadioButton("btn1 ");
jPanel1.add(btn1);
jpanel1.revalidate(); // as #Hovercraft Full Of Eels suggested
jPanel1.repaint();
}

JTabbedPane doesn't work correctly

public void tabbedPane(){
JPanel tab1 = new JPanel();
JButton btn = new JButton("Buton - 1");
btn.setPreferredSize(new Dimension(50, 20));
btn.setLocation(0, 10);
tab1.add(btn);
JTabbedPane tabPanel = new JTabbedPane();
tabPanel.addTab("tab1", null, tab1);
tabPanel.addTab("tab2", tab1);
tabPanel.addTab("tab3", btn);
tabPanel.setPreferredSize(new Dimension(450, 150));
tabPanel.setLocation(50, 0);
mainPanel.add(tabPanel);//Main panel on frame
}
When I run my application, I see only tab2 and tab3 pane, and I have many issues:
tabPanel.setLocation doesn't work
tabPanel.addTab("tab1" ...) doesn't work
btn.setPreferredSize(new Dimension(50, 20)); when I
click "tab2" it works correctly, however when I click "tab3" it doesn't change button
size.. why?
and i use null layout

tabPanel.setLocation doesn't work
Don't use setLocation(...) but instead use nested components and layout managers to achieve a pleasing and easy to maintain GUI layout.
tabPanel.addTab("tab1" ...) doesn't work
With Swing, you can only add a component to one container, that's it. The component will only show up in the last container that it was added to.
btn.setPreferredSize(new Dimension(50, 20)); when I click "tab2" it works correctly, however when I click "tab3" it doesn't change button size.. why?
Again, you will want to study the layout managers
and i use null layout
You almost never want to do this as this will make your application not look correct on any platform but your own and will make it very very difficult to maintain and upgrade. It is much better to use the layout managers and let them do the heavy lifting of laying out and sizing components for you.

What is your objective with this?
A JTabbedPane is used to organize views, I see you're trying to add a JPanel as a first tab, this is the 'main goal' of the JTabbedPanes.
tabPanel.addTab("Tab 1", tab1);
Try to add the tab like this, you're passing a 'null' value as the icon, which must not affect at all, but if you're not using an icon, then just add the panel as a tab with the intended name.
On second adding, you're adding again the same component (tab1).
On third adding, you're trying to add a component already on a container (tab1). This will make this component to appear only in the last container you add it to. Besides, component is a JButton. I cannot see the goal of a JButton as a tab.
For the setLocation(x, y) issue, check the layout you're using on the container.
Again, I think the main issue here is that you're not correctly approaching your problem, or you're not using the required tools.

not displaying all the buttons

I have an array with buttons:
JButton[] commandButtons = {
new JButton("Add Chair"),
new JButton("Add Table"),
new JButton("Add Desk"),
new JButton("Clear All"),
new JButton("Total Price"),
new JButton("Save"),
new JButton("Load"),
new JButton("Summary")
};
I want to put them all in the panel, but it is displaying only the last button.
so if anyone know how to fix it or have an advice it would be great.
Also I am not sure how to do the for loop as a for each.
for(int i=0; i<commandButtons.length; i++)
{
westPanel.add(commandButtons[i]);
commandButtons[i].addActionListener(this);
}

Set a FlowLayout manager on the westPanel JPanel and they will all show up.

I believe that you have not set layout, so the default one is BorderLayout. When you are adding elements to this layout without telling the parameter (where to put the element) it is added by default to the center. But there can be only one element in the center, so you see only the last button.
The fast fix is define flow layout:
pannel.setLayout(new FlowLayout());
Do it before adding the buttons. Now you will see all buttons. If you do not see enlarge the window.
Now, if the layout is not what you really want, read about layouts and decide which one (or combination of them) do you need.

Yeah it depends on the layout manager. If you want no layout manager you have to set the location and size yourself, otherwise they'll all be 0,0.
setLayout(null); //gives no layout manager
Always try to use a layout manager though.