Develop Reference

Java Swing show icon button and JLabel [duplicate]

So, i created an object of class "CustomPanel" that creates a JPanel with a GridLayout and a label inside of it then I added it to my JFrame. It works fine showing the label "HELLO", but when I change the layout manager of the jpanel to (null) it doesn't show anything. I know, I know using null layout is a very bad practice but I just want to know why it isn't showing the components.
Main class:
import javax.swing.JFrame;
public class MainMenu extends javax.swing.JFrame{
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Size the window.
frame.setSize(500, 500);
CustomPanel panel = new CustomPanel();
frame.getContentPane().add(panel);
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
CustomPanel class with GridLayout (This works fine):
import java.awt.GridLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class CustomPanel extends JPanel{
public CustomPanel() {
initUI();
}
public final void initUI() {
// create the panel and set the layout
JPanel main = new JPanel();
main.setLayout(new GridLayout());
// create the labels
JLabel myLabel = new JLabel("HELLO");
// add componets to panel
main.add(myLabel);
this.add(main);
}
}
CustomPanel class with Null layout (This doesn't work):
import javax.swing.JLabel;
import javax.swing.JPanel;
public class CustomPanel extends JPanel{
public CustomPanel() {
initUI();
}
public final void initUI() {
// create the panel and set the layout
JPanel main = new JPanel();
main.setLayout(null);
// create the labels
JLabel myLabel = new JLabel("HELLO");
myLabel.setBounds(10, 10, myLabel.getPreferredSize().width, myLabel.getPreferredSize().height);
// add componets to panel
main.add(myLabel);
this.add(main);
}
}
The jlabel is correctly set inside the jpanel so it should be showing in the upper-left side of the jframe, but it doesn't.
What is causing this? what am I missing?.

The problem is that when you don't use a proper layout manager the main JPanel has a preferred size of 0,0, and won't display within the container that it is placed within. The CustomPanel that holds the main JPanel uses FlowLayout and will use its contained component's preferred sizes to help size and position these components, but since main has no layout, adding the JLabel to main does not increase the preferred size as it should -- yet another reason to use layouts, and CustomPanel will display main as just a sizeless dot. You could of course get around this by giving main a preferred size via main.setPreferredSize(...), but then you'd be solving a kludge with a kludge -- not good. Another possible solution is to change CustomPanel's layout to something else that might expand the main JPanel that it holds, perhaps giving CustomPanel a BorderLayout. In this situation, adding main to CustomPanel in a default fashion will place the main JPanel into the BorderLayout.CENTER position, expanding it to fill CustomPanel, and the JLabel will likely be seen.
The proper solution, of course, is to avoid use of null layouts whenever possible.

JPanel Class with null layout not showing components

So, i created an object of class "CustomPanel" that creates a JPanel with a GridLayout and a label inside of it then I added it to my JFrame. It works fine showing the label "HELLO", but when I change the layout manager of the jpanel to (null) it doesn't show anything. I know, I know using null layout is a very bad practice but I just want to know why it isn't showing the components.
Main class:
import javax.swing.JFrame;
public class MainMenu extends javax.swing.JFrame{
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Size the window.
frame.setSize(500, 500);
CustomPanel panel = new CustomPanel();
frame.getContentPane().add(panel);
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
CustomPanel class with GridLayout (This works fine):
import java.awt.GridLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class CustomPanel extends JPanel{
public CustomPanel() {
initUI();
}
public final void initUI() {
// create the panel and set the layout
JPanel main = new JPanel();
main.setLayout(new GridLayout());
// create the labels
JLabel myLabel = new JLabel("HELLO");
// add componets to panel
main.add(myLabel);
this.add(main);
}
}
CustomPanel class with Null layout (This doesn't work):
import javax.swing.JLabel;
import javax.swing.JPanel;
public class CustomPanel extends JPanel{
public CustomPanel() {
initUI();
}
public final void initUI() {
// create the panel and set the layout
JPanel main = new JPanel();
main.setLayout(null);
// create the labels
JLabel myLabel = new JLabel("HELLO");
myLabel.setBounds(10, 10, myLabel.getPreferredSize().width, myLabel.getPreferredSize().height);
// add componets to panel
main.add(myLabel);
this.add(main);
}
}
The jlabel is correctly set inside the jpanel so it should be showing in the upper-left side of the jframe, but it doesn't.
What is causing this? what am I missing?.

The problem is that when you don't use a proper layout manager the main JPanel has a preferred size of 0,0, and won't display within the container that it is placed within. The CustomPanel that holds the main JPanel uses FlowLayout and will use its contained component's preferred sizes to help size and position these components, but since main has no layout, adding the JLabel to main does not increase the preferred size as it should -- yet another reason to use layouts, and CustomPanel will display main as just a sizeless dot. You could of course get around this by giving main a preferred size via main.setPreferredSize(...), but then you'd be solving a kludge with a kludge -- not good. Another possible solution is to change CustomPanel's layout to something else that might expand the main JPanel that it holds, perhaps giving CustomPanel a BorderLayout. In this situation, adding main to CustomPanel in a default fashion will place the main JPanel into the BorderLayout.CENTER position, expanding it to fill CustomPanel, and the JLabel will likely be seen.
The proper solution, of course, is to avoid use of null layouts whenever possible.

JScrollPane doesn't work with JTextArea

I'm trying to add the ScrollPane to my TextArea, but it doesn't appear.
Here's the code:
import javax.swing.*;
public class PracownikGui extends JFrame {
private JPanel Panelek;
private JTextArea Tekscik;
private JScrollPane Skrol;
public PracownikGui() {
setMinimumSize(new Dimension(600, 600));
setLocationRelativeTo(null);
setContentPane(Panelek);
setResizable(false);
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
Tekscik();
public void Tekscik() {
Tekscik = new JTextArea(2, 10);
Skrol = new JScrollPane( Tekscik );
Tekscik.setSize(300, 300);
Tekscik.setLocation(20, 70);
Tekscik.setEditable(true);
Tekscik.setLineWrap(true);
add(Tekscik);
}}
Any help, please.

You're shooting yourself in the foot by setting a JTextArea's size or preferredSize since this prevents it from expanding into the JScrollPane:
Tekscik.setSize(300, 300);
set its rows and columns only.
Also you need to add the JScrollPane to the GUI, not the JTextArea.
Also, while null layouts and setBounds() or setSize(...) and setLocation(...) might seem to Swing newbies like the easiest and best way to create complex GUI's, the more Swing GUI'S you create the more serious difficulties you will run into when using them. They won't resize your components when the GUI resizes, they are a royal witch to enhance or maintain, they fail completely when placed in scrollpanes, they look gawd-awful when viewed on all platforms or screen resolutions that are different from the original one.
e.g.,
import javax.swing.*;
public class PracownikPanel extends JPanel {
private JTextArea tekscik = new JTextArea(5, 25);
public PracownikPanel() {
tekscik.setLineWrap(true);
tekscik.setWrapStyleWord(true);
JScrollPane skrol = new JScrollPane(tekscik);
skrol.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
add(skrol);
}
private static void createAndShowGui() {
PracownikPanel mainPanel = new PracownikPanel();
JFrame frame = new JFrame("PracownikPanel");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

I made quite a few changes to your code. Your code wouldn't run.
Here's the GUI I created.
As you can see, there's a vertical scroll bar. The default action for the scroll bar is that it doesn't appear until you've filled the JTextArea with text.
Here are the important changes I made to your code.
Class names start with a capital letter. Method names and variable names start with a lower case letter.
A Swing application must start with a call to the SwingUtilities invokeLater method. This ensures that the Swing components are created and used on the Event Dispatch thread (EDT). Since the invokeLater method requires a Runnable, I had the PracownikGui class implement Runnable.
You use Swing components. You don't extend Swing components, or any other Java class, unless you want to override one of the methods in that class.
I removed all of the sizing and positioning statements, except for the statement that defines the rows and columns of the JTextArea. Hovercraft Full Of Eels explained this, but you use Swing layouts to get the arrangement of Swing components you want. The default layout for a JPanel is the FlowLayout. The default layout for a JFrame is the BorderLayout.
I added the JScrollPane to the JPanel. I added the JPanel to the JFrame.
Here's the code.
package com.ggl.testing;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
public class PracownikGui implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new PracownikGui());
}
private JFrame frame;
private JPanel panelek;
private JTextArea tekscik;
private JScrollPane skrol;
#Override
public void run() {
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
panelek = new JPanel();
tekscik(panelek);
frame.setContentPane(panelek);
frame.setResizable(false);
frame.pack();
frame.setVisible(true);
}
public void tekscik(JPanel panelek) {
tekscik = new JTextArea(2, 20);
tekscik.setEditable(true);
tekscik.setLineWrap(true);
skrol = new JScrollPane(tekscik);
panelek.add(skrol);
}
}

New JCheckboxes not appearing below eachother

I am trying to make a basic program where whenever you press a button, a JCheckbox is generated and added below the other JCheckbox on a panel. I figured out how to generate the JCheckbox with a ActionListener but I can't figure out how to get each new check box to appear below the previous one. Everything else seems to be working but I can't get this location thing to work.
box.setVisible(true);
_p.add(box);
int i = 0;
int u = i++;
box.setAlignmentX(0);
box.setAlignmentY(u);
Here is a sample of my code. I've been stuck on this problem for a very long time and would greatly appreciate any and all help.

Check out the Swing tutorial on Using Layout Managers. You could use a vertical BoxLayout or a GridBagLayout or maybe a GridLayout.
Whatever layout you choose to use the basic code for adding components to a visible GUI is:
panel.add(...);
panel.revalidate();
panel.repaint();
The other statements in your code are not necessary:
//box.setVisible(true); // components are visible by default
The following methods do not set a grid position.
//box.setAlignmentX(0);
//box.setAlignmentY(u);

JCheckbox lives in a container like a JPanel (that means that you add checkbox to a panel) . A JPanel have a layoutManager. Take a look about Using Layout Managers
You could use BoxLayout with Y_AXIS orientation or a GridLayout with 1 column and n rows.
Example:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class CheckBoxTest {
private JPanel panel;
private int counter=0;
public CheckBoxTest(){
panel = new JPanel();
panel.setLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));
JButton button = new JButton(" Add checkbox ");
button.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent evt){
panel.add(new JCheckBox("CheckBox"+Integer.toString(counter++)));
//now tell the view to show the new components added
panel.revalidate();
panel.repaint();
//optional sizes the window again to show all the checkbox
SwingUtilities.windowForComponent(panel).pack();
}
});
panel.add(button);
}
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("Checkbox example");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setLocationByPlatform(Boolean.TRUE);
CheckBoxTest test = new CheckBoxTest();
frame.add(test.panel);
//sizes components
frame.pack();
frame.setVisible(Boolean.TRUE);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}

JLabel alignment in JPanel

I'm trying to align a JLabel to the right in a JPanel. I'm adding a JTabbedPane, a JPanel which contains my JLabel and JTextArea to a main JPanel.
I have searched SO and tried some methods like setAlignmentX, setHorizontalAlignment(SwingConstants.LEFT) and nested containers to no avail.
Here's my code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class LabelProblem
{
public static void main(String[] args)
{
JFrame frame = new JFrame("Label Problem");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel Main = new JPanel();
Main.setLayout(new BoxLayout(Main, BoxLayout.Y_AXIS));
JPanel ComponentPanel = new JPanel();
JLabel label = new JLabel("Sample Text");
label.setHorizontalAlignment(SwingConstants.LEFT);
label.setBorder(BorderFactory.createLineBorder(Color.BLACK));
label.setAlignmentX(Component.RIGHT_ALIGNMENT);
ComponentPanel.add(label);
JTabbedPane Tab = new JTabbedPane();
Tab.add("Document 1", new JPanel());
Main.add(Tab);
Main.add(ComponentPanel);
JTextArea Area = new JTextArea(10,10);
JScrollPane Scroll = new JScrollPane(Area);
frame.add(Main);
frame.add(Scroll, BorderLayout.SOUTH);
frame.setSize(450,450);
frame.setVisible(true);
}
}
How can I align my JLabel to the right?
Thanks!

So, the place of that label is determined by the layout of ComponentPanel. Since you didn't specify any layout it is using the default FlowLayout with a CENTER alignment. Assuming that you are ok with a FlowLayout it is a mere question of setting the alignment of the LEFT since this is possible with this layout.
Here's the code with the fix, however I suspect that as you put more elements to the ComponentPanel you will want to use another layout since FlowLayout is more adequate for menus and the like and not for displaying the main content.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.FlowLayout;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTabbedPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
class LabelProblem
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
initGUI();
}
});
}
public static void initGUI()
{
JFrame frame = new JFrame("Label Problem");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel main = new JPanel();
main.setLayout(new BoxLayout(main, BoxLayout.Y_AXIS));
JPanel componentPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
JLabel label = new JLabel("Sample Text");
label.setBorder(BorderFactory.createLineBorder(Color.BLACK));
componentPanel.add(label);
JTabbedPane Tab = new JTabbedPane();
Tab.add("Document 1", new JPanel());
main.add(Tab);
main.add(componentPanel);
JTextArea area = new JTextArea(10, 10);
JScrollPane scroll = new JScrollPane(area);
frame.add(main);
frame.add(scroll, BorderLayout.SOUTH);
frame.setSize(450, 450);
frame.setVisible(true);
}
}
Result:
Note: I also changed the variable names to follow the java style convention: variable names should start with lower case to differenciate them from clases names, starting in upper case.

One simple approach is to set the label's horizontalAlignment to JLabel.RIGHT in the constructor.
import java.awt.*;
import javax.swing.*;
class LabelProblem {
public static void main(String[] args) {
JFrame frame = new JFrame("Label Problem");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridLayout(0, 1));
JTabbedPane tab = new JTabbedPane();
tab.add("Document 1", new JPanel());
frame.add(tab);
JLabel label = new JLabel("Sample Text", JLabel.RIGHT);
frame.add(label);
JTextArea area = new JTextArea(10, 10);
JScrollPane scroll = new JScrollPane(area);
frame.add(scroll);
frame.pack();
frame.setSize(450, 450);
frame.setVisible(true);
}
}

I think it may be a matter of you not actually setting layouts where you imagine you're setting layouts.
You have a JPanel with a vertically oriented BoxLayout (Main) enclosing another JPanel with default layout (ComponentPanel), finally enclosing your label. The reason why your label can't be pushed to the right is because is already is pushed to the right within it's enclosing container. If you set a colored border around ComponentPanel, you'll see what I mean -- it only occupies the same amount of space as the JLabel, giving the JLabel nowhere to move.
You need to set a layout and constraints for your intermediate ComponentPanel, allowing it to horizontally fill its parent container so that the label has someplace to go.
You haven't really specified how your layout is supposed to look, but if you change the layout on Main to X_AXIS, your label will pop over to the left (as will its parent container). Without knowing what you're really trying to do, I can't say much more.
I would however, suggest you throw your BoxLayout away entirely and look into using GridBagLayout, which gives you a high level control over your UI. GridBagLayout isn't the most concise construct, but that's the price of control.