Develop Reference

Java - My action event doesn't work

I'm learning Java and Swing, but my JButton doesn't work.
import javax.swing.JFrame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class Programma {
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}
catch (Exception e){
e.printStackTrace();
}
JFrame frame = new JFrame("DIG");
JPanel panel = new JPanel();
JButton button = new JButton("Click Me");
frame.setSize(400, 400);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
button.setBounds(100, 100, 130, 35);
panel.add(button);
frame.add(panel);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
JLabel label = new JLabel("Hello World");
label.setVisible(true);
panel.add(label);
}
});
}
}
The frame and button are visible, nut when I click it, the label doesn't appear. How can I fix this?
Do I write this before the other component like JPanel, JButton, etc., or do I write this at the end of code:
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
What is the difference ?
By the way, button.setBounds(100, 100, 130, 35) doesn't work, either.

I see some issues in your code:
button.setBounds(100, 100, 130, 35); that line will be ignored and you shouldn't be manually be determining the position of the components. See Null layout is evil and Why is it frowned upon to use a null layout in swing? altough you're not using null layout, there is explained why you shouldn't be manually determining the positions of the components.
You're running everything in your program in the main method, that will be hard to maintain later.
You're calling frame.setVisible(true) before you've added all your elements to it, that will cause you random issues.
You're not running your program on the Event Dispatch Thread (EDT), you can solve this by starting your program with the following code, which places it in the EDT. It's recommended as Swing is not thread safe.
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
//Your constructor here
}
});
}
You're setting the size of the JFrame with setSize(...), instead call frame.pack() and override the getPreferredSize() method of the JPanel.
After all the above has been said, you need to call revalidate() and repaint() on your ActionListener so your program paints its new state.
This program follows all the above recommendations and produces the following outputs (before clicking and after clicking the button 3 times), I on purpose to not make the images so large, made the GUI shorter (200 x 200 instead of 400 x 400)
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Programma {
private JFrame frame;
private JPanel panel;
private JButton button;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Programma().createAndShowGui();
}
});
}
public void createAndShowGui() {
frame = new JFrame("DIG");
panel = new JPanel() {
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
};
button = new JButton("Click Me");
panel.add(button);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JLabel label = new JLabel("Hello World");
panel.add(label);
panel.revalidate();
panel.repaint();
}
});
frame.add(panel);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
Do i write this before the other componente like JPanel,JButton... or do i write this at the end of code ?
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
What is the difference ?
Altough I answered this on the recommendations, the difference is that if you call setVisible before adding all your elements to the frame, then you'll find yourself with some random issues where the components are not all visible until you pass your mouse over them (or where they should be). frame.pack() and setVisible should be the last ones to be called in your program, and frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); can be at the start or the end, it doesn't affects, but I prefer to have it at the end too.
button.setBounds(100, 100, 130, 35); doesn't work too.
Well, that's because of you're using a layout manager (and that's the right way to do your GUIs) instead of a null-layout (which you shouldn't be using anyway) (See point #1).
Edit
What is the difference between frame.setSize(); and frame.setpack() ?
If you read the docs for pack():
Causes this Window to be sized to fit the preferred size and layouts of its subcomponents. The resulting width and height of the window are automatically enlarged if either of dimensions is less than the minimum size as specified by the previous call to the setMinimumSize method.
So, it will calculate the minimum size for your JFrame where all the elements are visible and in their preferred size while setSize will only set the window size, but if you place a JScrollBar inside it for example this will reduce the window size, because of that, that's why you should override the getPreferredSize(...) method of your container, so it will calculate its preferred size including the width of the JScrollBar or some other elements that could modify its size. See Should I avoid the use of setPreferred|Maximum|MinimumSize in Swing? (the general consensus says yes)

When you add components dynamically to panel, you need to repain it.
Do this
panel.revalidate();
after
panel.add(label);

Negative coordinates of JPanels (and lack of cooperation with Timer)

Please note that this is a more theoretical question about problems with this approach, as I'm trying to understand the underlying mechanics - genuine curiosity. For the actual implementation I'm likely to use something different.
Say we have the following frame with a split pane. The right hand side of the split pane has a button to slide out a panel on the left and show another one in its place (here I'm using overlay layout to make it look smoother). The code is as follows:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import javax.swing.OverlayLayout;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class Main {
JPanel panel;
JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
public void makeUI() {
panel = new JPanel();
panel.setBackground(Color.RED);
panel.setLocation(0,0);
JPanel panel3 = new JPanel();
panel3.setBackground(Color.BLUE);
panel3.setMinimumSize(new Dimension(100,400));
JPanel panelContainer = new JPanel();
panelContainer.setLayout(new OverlayLayout(panelContainer));
panelContainer.add(panel);
panelContainer.add(panel3);
JButton button = new JButton("slide out");
// Slide out the red panel to reveal blue
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
((JButton) e.getSource()).setEnabled(false);
new Timer(1, new ActionListener() {
public void actionPerformed(ActionEvent e) {
panel.setLocation(panel.getX() - 1, 0);
if (panel.getX() + panel.getWidth() == 0) {
((Timer) e.getSource()).stop();
panel.setVisible(false);
System.out.println("Timer stopped");
}
}
}).start();
}
});
JFrame frame = new JFrame("Sliding Panel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
frame.setLayout(null);
splitPane.setDividerLocation(100);
splitPane.setLeftComponent(panelContainer);
JPanel panel2 = new JPanel();
panel2.add(button);
// panel2.add(button2);
panel2.setMinimumSize(new Dimension(200,400));
splitPane.setRightComponent(panel2);
frame.setContentPane(splitPane);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new Main().makeUI();
}
});
}
}
Now if I add a button that reverses the animation, by setting location to (-panel.getWidth(), 0) and then increase the x coordinate, this fails. In theory the code is the same, with the only differences being in the start position, end position, and increments. However it does no longer work.
JButton button2 = new JButton("slide in");
button2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
((JButton) e.getSource()).setEnabled(false);
panel.setVisible(true);
panel.setLocation(-panel.getWidth(),0);
System.out.println(panel.getX()); // gives -99, which is about right
new Timer(1, new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println(panel.getX()); // starts from 0
panel.setLocation(panel.getX() + 1, 0);
System.out.println(panel.getX()); // keeps increasing until forcibly stopped
if (panel.getX() == 0) {
((Timer) e.getSource()).stop();
System.out.println("Timer stopped");
}
}
}).start();
}
});
More precisely the problem lies in the new Timer(...) line. As per console logging, setting location puts the X coordinate at -99, but two lines later it's at 0, and when increments occur, it goes on to infinity.
Perhaps I am misunderstanding how timers work, however after reading the documentation on it and JPanels, I still don't see why such an approach would not work. Not to mention that there is very little on negative coordinates of JPanels to begin with.
Thank you in advance for all the explanations!
EDIT (27.07.2016)
#camickr 's answer makes it work, however I still don't undersand it, although it helped me narrow the question a little:
Why is the layout re-done after setting the location to negative? What is causing it to be re-done?

In theory the code is the same, with the only differences being in the start position, end position, and increments
Actually it is not the same.
You play with the visibility of the panel and the logic is different depending on which button you click. I'm guessing the setVisible(true) statement is invoking the layout manager which is resetting the location of the component.
There is no need to change the visibility of the panel. Get rid of both setVisible(...) statements.
Also, you might want to keep the buttons enabled you can test sliding in/out repeatedly without restarting the program.
Edit:
if that was the case, why does getX() gives -99
Because the layout hasn't been done when that statement is executed.
Code does not always execute sequentially. Sometimes Swing methods will use SwingUtiltites.invokeLater() to add code the end of the Event Dispatch Thread (EDT).
This is easy enough to verify. Just change your code as follows to see when the layout is invoked.
JPanel panelContainer = new JPanel()
{
#Override
public void doLayout()
{
System.out.println("layout");
super.doLayout();
}
};

How to add action to a button?

I am trying to enter an event for JButon I create:
JButton botton1=new JButton("welcom to my show db! lets start");
botton1.setFont(new Font ("Eras Medium ITC",Font.BOLD,20));
this.add(botton1);
JPanel Basic_panel=new JPanel();
Basic_panel.setName("SHOW DB ");
Basic_panel.setBounds(x,y,width,hight);
botton1.addActionListener(this) ;
}
public void actionPerformed(ActionEvent e) {
if (e.getSource()==botton1){
Now I want to enter another JFrame I made, and make the first disappear. How?

For your original question:
How to add action to a button?
you might want to check How to write an Action Listener.
For your second question:
Now I want to enter another JFrame I made, and make the first disappear. How?
please check both approaches :)
Option 1 (Recommended)
If you want to do it the right way, you should use a CardLayout as recommended by #AndrewThompson in his comment above.
I also saw you were using a Null Layout (because of setBounds() method), you might also want to get rid of it, see Why is it frowned upon to use a null layout in Swing? and Null Layout is Evil to know why, insted you should be using a Layout Manager or combinations of them as shown in the following code based on #AndrewThompson's answer (The same that was linked in his comment above) but a bit modified to work with a JFrame instead of a JOptionPane, so give him credit by upvoting his Original Answer too!
This produces the following outputs:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class CardLayoutDemo {
JButton button1, button2;
CardLayoutDemo() {
JFrame gui = new JFrame("CardLayoutDemo");
button1 = new JButton("Go to pane 2");
button2 = new JButton("Go to pane 1");
JPanel pane1 = new JPanel();
pane1.setLayout(new BoxLayout(pane1, BoxLayout.PAGE_AXIS));
JPanel pane2 = new JPanel();
pane2.setLayout(new BoxLayout(pane2, BoxLayout.PAGE_AXIS));
final CardLayout cl = new CardLayout();
final JPanel cards = new JPanel(cl);
pane1.add(new JLabel("This is my pane 1"));
pane1.add(button1);
pane2.add(new JLabel("This is my pane 2"));
pane2.add(button2);
gui.add(cards);
cards.add(pane1, "frame1");
cards.add(pane2, "frame2");
ActionListener al = new ActionListener(){
public void actionPerformed(ActionEvent ae) {
if (ae.getSource() == button1) {
cl.show(cards, "frame2");
} else if (ae.getSource() == button2) {
cl.show(cards, "frame1");
}
}
};
button1.addActionListener(al);
button2.addActionListener(al);
gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
gui.pack();
gui.setVisible(true);
}
public static void main(String[] args) {
new CardLayoutDemo();
}
}
With this option you only have 1 JFrame but you can change through different views, and you don't annoy user with multiple windows on the task bar.
One more tip here is: If you're going to open this second JFrame to prevent user from doing something on the 1st one, you should consider using a JOptionPane or this second JFrame will contain just a bit information which you don't want to have there for the whole time (Something like a pop up).
Option 2 (Not recommended)
But if you really really really want to use multiple JFrames (which is not recommended) you can dispose() it. At the time you're calling your new JFrame to be created. For example, the following code produces this output:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class TwoJFrames {
JFrame frame;
JButton button;
TwoJFrames() {
frame = new JFrame("1st frame");
button = new JButton("Click me!");
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
new AnotherFrame();
frame.dispose();
}
});
frame.add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
public static void main(String args[]) {
new TwoJFrames();
}
class AnotherFrame {
JFrame frame2;
JLabel label;
AnotherFrame() {
frame2 = new JFrame("Second Frame");
label = new JLabel("This is my second frame");
frame2.add(label);
frame2.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame2.pack();
frame2.setVisible(true);
}
}
}
In this case you might want to consider setVisible() instead if you want to go back to previous state or reopen this one when closing the second JFrame
Both of my above codes are called a Minimal, Complete, and Verifiable example (MCVE) or Runnable Example or Short, Self Contained, Correct Example (SSCCE) which are code you can copy-paste and see the same output as me, when you have an error in your code, these examples are very handy because we can see where your errors are or be able to find them easier and/or faster.
You should consider reading all the links I provided (included these ones) and for your future questions to make something like I've done above, that way you'll prevent confusion and you'll get more, faster and better responses.

I created my GUI in a GUI class' constructor. How would I access its Frames, Panels etc. from another class?

First of all, this is a more specific question than it seems to be. To start off: I am currently doing a small application with a rather small GUI, so I decided to make a GUI class, and initialize my whole GUI in this constructor.
This would look like this:
public class GUI extends JFrame{
public GUI{
//Initialize GUI here, including its Frames, Panels, Buttons etc.
}
}
How can I now access the GUIs frame etc. from an external class? If I would create an object of the GUI class, I would simply duplicate my GUI window. I did not come across any other ideas than making the frame, panel and so on static.
I'm somewhat lost right now. Also I'm pretty sure that I am not thinking the right way into this case, but I need someone to point me to the right direction. If someone could help me out, I would be very thankful.

First of all, using static is the worst solution possible, even if your GUI class is a singleton (buf if it is, at least it will work fine).
Why don't you simply create getters and/or setters ? And finally, it is usually not normal that external classes need to access the components of another graphic class. You should wonder if your design is the most fitted for your needs.

Here's a simple GUI to change the background color of a JPanel with a JButton. Generally, this is how you construct a Swing GUI.
package com.ggl.testing;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class ChangeDemo implements Runnable {
private boolean isYellow;
private JFrame frame;
public static void main(String[] args) {
SwingUtilities.invokeLater(new ChangeDemo());
}
#Override
public void run() {
frame = new JFrame("Change Background Demo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel mainPanel = new JPanel();
mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.PAGE_AXIS));
JPanel namePanel = new JPanel();
JLabel nameLabel = new JLabel(
"Click the button to change the background color");
nameLabel.setAlignmentX(JLabel.CENTER_ALIGNMENT);
namePanel.add(nameLabel);
mainPanel.add(namePanel);
final JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new FlowLayout());
buttonPanel.setBackground(Color.YELLOW);
isYellow = true;
JButton changeButton = new JButton("Change Color");
changeButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent event) {
isYellow = !isYellow;
if (isYellow) buttonPanel.setBackground(Color.YELLOW);
else buttonPanel.setBackground(Color.RED);
}
});
buttonPanel.add(changeButton);
mainPanel.add(buttonPanel);
frame.add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
}
You don't access the Swing components of the GUI from other classes. You create other classes to hold the values of the GUI.
Generally, you use the model / view / controller pattern to construct a Swing GUI. That way, you can focus on one part of the GUI at a time.
Take a look at my article, Java Swing File Browser, to see how the MVC pattern works with a typical Swing GUI.

You don't need to make it static or to create a new JFrame object every time.
Have a look at this simple code :
class UseJFrame {
public static void main(String...args) {
Scanner sc = new Scanner(System.in);
JFrame frame = new GUI();
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
System.out.println("Press E to exit");
String ip;
while(true) {
System.out.println("Show GUI (Y/N/E)? : ");
ip = sc.nextLine();
if(ip.equalsIgnoreCase("y") {
frame.setVisible(true);
} else if(ip.equalsIgnoreCase("n") {
frame.setVisible(false);
} else { // E or any other input
frame.dispose();
}
}
}
}
Note : Don't make GUI visible through constructor or it will show window at the very starting of creation of JFrame object.
If you want to use the same JFrame object at other places too then pool architecture would be better approach.

Bring JPanel to front of other objects in java (SWING)

I want to make a loading message when an app processes, so I used a JPanel over a JTree. But when the user clicks on the JPanel, the JTree will be selected and the JPanel will go to the back. After hiding the JPanel, it never shows again. I don't know why, but it seems it never go in front of the JTree.
I need a way to bring the JPanel in front of everything. How can I do this?
EDIT: Also I must mention that I don't want a JDialog. I want to use the JPanel on top of any element to show a loading message until a process finishes.

So here you have at least two solutions. Either go with what #Geoff and #sthupahsmaht are suggesting. BTW also possible is to use JOptionPane which automatically creates a dialog for you.
The other option would be to use a GlassPane from a frame.
Or yet another option is to use JLayeredPane as #jzd suggests.
EDIT:
Example showing how to use GlassPane to capture user selections.
Try following steps:
1.Left clicking on the glass pane visible at start. See the output.
2.Right click it. This hides the glass pane.
3.Left clicking on the content pane. See the output.
4.Right click it. Go to point 1.
Enjoy.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class OverPanel extends JPanel
{
private static void createAndShowGUI()
{
final JFrame f = new JFrame();
f.setPreferredSize(new Dimension(400, 300));
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel glassPanel = new JPanel();
glassPanel.setBackground(Color.RED);
glassPanel.addMouseListener(new MouseAdapter()
{
#Override
public void mousePressed(MouseEvent e)
{
super.mousePressed(e);
System.out.println("f.getGlassPane() mousePressed");
if(e.getButton() == MouseEvent.BUTTON3)
f.getGlassPane().setVisible(false);
}
});
f.setGlassPane(glassPanel);
f.getContentPane().setBackground(Color.GREEN);
f.getContentPane().addMouseListener(new MouseAdapter()
{
#Override
public void mousePressed(MouseEvent e)
{
super.mousePressed(e);
System.out.println("f.getContentPane() mousePressed");
if(e.getButton() == MouseEvent.BUTTON3)
f.getGlassPane().setVisible(true);
}
});
f.getGlassPane().setVisible(true);
f.pack();
f.setVisible(true);
}
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
createAndShowGUI();
}
});
}
}
EDIT2:
If you want to have an effect of a dialog, you can achieve it by incorporating appropriately this code into my example.
JPanel panel = new JPanel(new GridLayout(0, 1));
panel.setBorder(BorderFactory.createLineBorder(Color.BLACK, 2));
panel.setBackground(Color.YELLOW);
panel.add(new JLabel("I am message Label"));
panel.add(new JButton("CLOSE"));
JPanel glassPanel = new JPanel(new GridBagLayout());
glassPanel.setOpaque(false);
glassPanel.add(panel);

You need a to use a JLayeredPane for moving components in front of each other.
Here is a tutorial: How to use Layered Panes

Disabled Glass Pane might help you out.

It's not really clear how your code is organized. However, it sounds like what you might want is a modal dialog. Here's a link to a similar discussion with a number of referenced resources.
How to make a JFrame Modal in Swing java

Use JXLayer or JIDE Overlayable.

Jpanel main = new JPanel();
Jpanel a = new JPanel();
JPanel b = new Jpanel();
main.add(a);
main.add(b);
at this point the object:
a -> 0 ( index)
b -> 1 (index)
main.getComponentCount() = 2
main.setComponentZorder(b,0);
a -> 1
b -> 0;
b OVER
a DOWN

For those who have no problem using a JDialog, this is a sure way to get it to show up if you're having issues. Just make sure to control it properly if the dialog is modal, when disposing, setting focus etc.
JDialog dialog = new JDialog();
dialog.setAlwaysOnTop(true);