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);

Insert Button in JPanel

I am using swing in Java and I need to create a JButton and put it in a JPanel.
I reed tutorials and I did this:
public void crearNuevaMiga(String nombre)
{
JButton nuevo = new JButton(nombre);
this.MigasDePan.add(nuevo);
nuevo.setVisible(true);
nuevo.setLocation(new Point(migaX, migaY));
System.out.println(nuevo.getLocation().x + " "+ nuevo.getLocation().y);
migaX = migaX-avanceMigas;
}
I do that and when I call the function, I cant see the button. I put a button with the designer of NetBeans and get X and Y Location. Then, in the variables migaX and migaY I put that X and Y Location, so the button need to be in the same position, but it is not there.
Anyone knows why? Maybe putting the location in that way is not correct?
Thanks for your time!
EDIT: MigasDePan is my JPanel

Here's a simple example of putting a JButton in a JPanel, and putting the JPanel in a JFrame. I created this code without using any GUI builder.
I called the SwingUtilities invokeLater method in the main method to put the creation and use of the Swing components on the Event Dispatch thread. Oracle and I insist that you start every Swing application on the Event Dispatch thread.
I used a JFrame. You must call the JFrame methods in the order they are called in the run method.
I used a JPanel. I put the JButton in the middle of the JPanel, since it's the only component on the JPanel.
I used a Swing layout, the Border Layout. Different Swing layouts are used to create different Swing component layouts.
Here's the short, self-contained, runnable code.
package com.ggl.testing;
import java.awt.BorderLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class MyButton implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new MyButton());
}
#Override
public void run() {
JFrame frame = new JFrame("My Button");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(createMainPanel());
frame.pack();
frame.setVisible(true);
}
private JPanel createMainPanel() {
JPanel panel = new JPanel();
panel.setLayout(new BorderLayout());
JButton myButton = new JButton("My Button");
panel.add(myButton);
return panel;
}
}

By default components have a size of (0, 0) so there is nothing to paint.
When you dynamically add a button to a visible GUI you need to invoke the layout manager so the components size/location can be determined by the layout manager.
The basic code is:
panel.add(...);
panel.revalidate();
panel.repaint();

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);
}
}

My JFrame window won't appear

My JFrame window won't appear, though, by the tutorial I've been watching, I've been doing everything spot on, yet nothing happens. It doesn't even give me an error, which makes it so much worse. This is the code:
import javax.swing.*;
import java.awt.*;
public class Window {
public class Window {
public void newWindow() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
JLabel label = new JLabel("I am a star! A beautiful shining star!", SwingConstants.CENTER);
frame.getContentPane().add(label);
frame.setVisible(true);
}
}
(This is a second class, the main one properly links to this one)

JFrame uses a layout manager named BorderLayout by default. To see components added to the frame, you should refer to its javadocs. However, the easiest choice here is to use FlowLayout. You also should use JFrame's pack() method, which, according to Oracle:
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.
Thus, this should work for you:
import javax.swing.*;
import java.awt.*;
public class Window {
public void newWindow() {
JFrame frame = new JFrame();
frame.getContentPane().setLayout(new FlowLayout()); // specify the layout manager
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
JLabel label = new JLabel("I am a star! A beautiful shining star!", SwingConstants.CENTER);
frame.getContentPane().add(label);
frame.pack(); // handles sizing of the window
frame.setVisible(true);
}
}
Notice that I removed the duplicate public class Window declaration, which might have been the reason you didn't see a frame at all. If it's still not working for you, I think you aren't calling the newWindow() method. If you want the window to show by simply calling new Window();, then you should change public void newWindow() to public Window().

import javax.swing.*;
import java.awt.*;
public class Window {
public void newWindow() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("I am a star! A beautiful shining star!", SwingConstants.CENTER);
frame.getContentPane().add(label);
frame.setVisible(true);
frame.pack();
}
}

From what I see, your not setting the size of the JFrame. Try,
frame.setSize(500, 500);

Java JFrame Not Displayed (Just Titlebar)

I know this is something very simple, but as a complete Java newbie I'm missing it and someone pointing it out would be infinitely helpful. I've stared at the screen and moved things around and still nothing.
Screenshot:
http://i.imgur.com/dwH60.png
This is all that comes up when this is run.
fullGUI.java:
import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JRadioButton;
import javax.swing.JTextArea;
public class fullGUI extends JFrame
{
JFrame frame = new JFrame(); //creates frame
public fullGUI() // constructor
{
//setLayout(new BorderLayout());
//add(new shipGrid(), BorderLayout.NORTH);
//add(new shipGrid(), BorderLayout.NORTH);
add(new JRadioButton("Horizontal"), BorderLayout.WEST);
add(new JRadioButton("Vertical"), BorderLayout.WEST);
add(new JTextArea("Instructions to player will go here"), BorderLayout.CENTER);
frame.setSize(400,600);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("Battleship!");
frame.pack(); //sets appropriate size for frame
frame.setVisible(true);
}
}
...called by...
test.java
public class test
{
public static void main(String[] args)
{
new fullGUI();
}
}

name classes in Java from a capital letter
FullGUI already extends JFrame, so no need to create another JFrame inside it
call getContentPane.add() to add to JFrame
use SwingUtilities.invokeLater
So overall something like this
import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JRadioButton;
import javax.swing.JTextArea;
public class FullGUI extends JFrame
{
public FullGUI() // constructor
{
getContentPane().add(new JRadioButton("Horizontal"), BorderLayout.WEST);
getContentPane().add(new JRadioButton("Vertical"), BorderLayout.WEST);
getContentPane().add(new JTextArea("Instructions to player will go here"), BorderLayout.CENTER);
setSize(400,600);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setTitle("Battleship!");
pack(); //sets appropriate size for frame
setVisible(true);
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new FillGU();
}
});
}

Problem is that you are extending JFrame in your class and creating new object "frame". You're adding components such as JRadioButton or JTextArea into fullGUI and other settings of the JFrame are applicable to frame object. It's up to you which approach you're going to choose, but pick one of them. You can extend JFrame and your class will be a child of JFrame which means you can call all public or protected methods from parent class, no need to create new instance of JFrame. Other way is to not extend JFrame and you have to create new JFrame object instead.

frame.pack() is causing your JFrame to resize according to its contents.
If you have frame.setSize(400,600), even if you don't add anything to its content pane,
the frame will be displayed with size 400x600.
But when you call frame.pack(), the frame will resize. In your case, your frame's content pane does not contain anything. Therefore the pack() method resizes it to only your title bar.

As Nikolay Kuznetsov said in earlier answer, you have extended Jframe in fullGUI so no need to create new Jframe in that class, because every instance of FullGUI will be a new frame.
With you code what happened is that you have created a Frame, say frame1 and instance of fullGUI(In main Method) say frame2, these are two different frames. In the Constructor you have added those controls to the frame2 (add()==this.add()) and said frame1.setvisible(true);
Adding controls to one frame and displaying altogether different frame is the reason why you were unable to see anything on output scree though you would have maximized the screen.