Develop Reference

JPanel not showing inside JFrame in Java

I know this question has been asked a lot and I have done my research but still can not find anything. Below is proof of this before anyone gets upset:
I found this link:
https://coderanch.com/t/563764/java/Blank-Frame-Panel
and this:
Adding panels to frame, but not showing when app is run
and this:
Why shouldn't I call setVisible(true) before adding components?
and this:
JPanel not showing in JFrame?
But the first question says use repaint which I tried with no fix and the second and third to last questions talk about putting setVisible after components added which I have.
The last one talks about making the users JPanelArt a extension (done so) of JPanel instead of JFrame and not to make a frame in a frame constructor (also have not done)
When ever I run this I just get a blank frame, as if the panel was never added in.
I apologise if I have missed something in those links. Anyway below is my classes:
GUI.java (extends JFrame)
package javaapplication2;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class GUI extends JFrame{
public GUI(String name) {
super(name);
getContentPane().setLayout(null);
JPanel myPanel1 = new GUIPanel();
myPanel1.setLocation(20, 20);
getContentPane().add(myPanel1);
setDefaultCloseOperation(EXIT_ON_CLOSE);
pack();
setResizable(true);
}
public static void main(String[] args) {
JFrame frame = new GUI("Game");
frame.setVisible(true);
}
}
GUIPanel.java (extends JPanel)
package javaapplication2;
import java.awt.*;
import javax.swing.*;
public class GUIPanel extends JPanel {
JButton start;
JButton inspect1;
JButton inspect2;
JButton inspect3;
JButton suspect;
public GUIPanel() {
setLayout(new BorderLayout());
start = new JButton("Start Game");
inspect1 = new JButton("Inspect 1");
inspect2 = new JButton("Inspect 2");
inspect3 = new JButton("Inspect 3");
suspect = new JButton("Choose Suspect");
add(start, BorderLayout.WEST);
add(inspect1, BorderLayout.WEST);
add(inspect2, BorderLayout.WEST);
add(inspect3, BorderLayout.WEST);
add(suspect, BorderLayout.WEST);
}
}
I know it is very simple, but that is because I am following a tutorial from my lecturer to get the hang of things as I previously used a GUI builder which someone in this community pointed out to me is not good to start with (very correct!)

The issue lies in your GUI class when you call getContentPane().setLayout(null). Because of this method call, your JFrame is not displaying anything. If you remove it, your elements should show up.
I also noticed that you were setting each JButton to have a constraint of BorderLayout.WEST. This will most likely put your JButtons on top of each other and render only one of them.

Put one JPanel onto another JPanel from a different Java class

I'm developing Java Swing application. My application has two Java classes. Inside class1.java, I include JFrame, JButton and JPanel (panel1). When I click the button I want to hide panel1 and should be shown panel2 of class2.java. I tried this method in button actionPerformed method of class1.java. But it was not working.
class2 pnl = new class2();
this.remove(panel1);
this.add(pnl);
this.validate();
this.repaint();

Analysis
You simply want the JComponents to be displayed on the JFrame. We can achieve this by using a single JPanel, but adding and removing the JComponents from it, during the JButton's action listener.
Without looking at your actual code, it is better to make a manageable way to reach code and instantiated Objects. The code listed below, creates a nice and manageable way to do so.
Achieving This
The entire class is listed below with comments for explanations.
package swing;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MultiPaneledFrame {
JFrame frame = new JFrame();
JPanel window = new JPanel();
// As you can see, we create an array containing all your JComponents.
// We have two of these, to simulate multiple JPanel's.
List<JComponent> window1Contents = new ArrayList<JComponent>();
List<JComponent> window2Contents = new ArrayList<JComponent>();
// NOTE: The above Lists can instead be stuck in their own class like asked for,
// and instantiated on Class invocation.
JButton goto2 = new JButton("Goto Panel 2");
JButton goto1 = new JButton("Goto Panel 1");
int panelToShow = 0; // 0 - First "panel".
// 1 - Second "panel".
// Main method of class. Change 'Multi_Paneled_Frame' to the name of your Class.
public MultiPaneledFrame() {
// Execute anything else you want here, before we start the frame.
window1Contents.add(goto2);
window2Contents.add(goto1);
// Here is where I personally am setting the coordinates of the JButton's on the JPanel.
goto2.setPreferredSize(new Dimension(200, 100));
goto1.setPreferredSize(new Dimension(200, 100));
//goto2.setBounds(5, 5, 150, 30); < Used for 'null' layout.
//goto1.setBounds(5, 5, 150, 30); < Used for 'null' layout.
goto2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
addComponents(panelToShow = 1);
}
});
goto1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
addComponents(panelToShow = 0);
}
});
initialiseFrame();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new MultiPaneledFrame();
}
});
}
private void initialiseFrame() {
frame.setSize(600, 400); // Change it accordingly.
// Optional
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setResizable(false);
// Needed
frame.setVisible(true);
frame.add(window);
window.setLayout(new BorderLayout()); // Assuming your using a BorderLayout.
//window.setLayout(null); < Uses 'null' layout.
addComponents(panelToShow);
// I always like to make sure that everything is on the frame nicely.
frame.repaint();
frame.validate();
}
private void addComponents(int panelNo) {
if (panelNo == 0) {
for (JComponent component : window1Contents) {
window.removeAll(); // We're removing everything that it contains and replacing it...
window.revalidate();
window.add(component, BorderLayout.CENTER);
//window.add(component); < Uses 'null' layout.
// Since we are using the first panel, we are adding
// everything from the first list of components to the window...
}
} else {
for (JComponent component : window2Contents) {
window.removeAll(); // We're removing everything that it contains and replacing it...
window.revalidate();
window.add(component, BorderLayout.CENTER);
//window.add(component); < Uses 'null' layout.
// Since we are using the second panel, we are adding
// everything from the second list of components to the window...
}
}
// Refreshes the frame.
frame.repaint();
frame.validate();
}
}
Conclusion
Although there are countless ways to achieve something like this, the way I have given, is semi-efficient, and very flexible. Feel free to edit the code, or drop a question if you have any concerns, and I will be happy to respond.
PS: This code was tested and works on a Macbook Air running OS X 10.11 and Java Version 8 Update 65.

CardLayout should be your solution. In this tutorial they show how to switch from panel to another one by selecting a value in ComboBox.
A little bit of explanation for the CarLayout:
The CardLayout lets you place different panel on top of each other but shows only one at the time. With your code, you select the one you want to display.
Initialisation:
this.setLayout(new CardLayout());
class1 pnl1 = new class1();
class2 pnl2 = new class2();
this.add(pnl1, "PANEL1");
this.add(pnl2, "PANEL2");
On your button actionPerformed:
CardLayout cl = (CardLayout)(this.getLayout());
cl.show(this, "PANEL2");

How do I create 2 frames in Java and Link them together?

I just created a GUI, now I want to create another GUI and link both together.
So on the first GUI when the user selects 'next' button, the second GUI is displayed.
For this, do I have to create a new class and just create a GUI again?
Here is what I have now:
import java.awt.Color;
import javax.swing.*;
public class Wizard {
private JLabel lblPicture;
private JRadioButton btLdap, btKerbegos, btSpnego, btSaml2;
private JButton btNext;
private JPanel panel;
public static void main(String[] args) {
new Wizard();
}
public Wizard() {
JFrame frame = new JFrame("Wizard");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(600,360);
frame.setVisible(true);
MyPanel();
RadioButtons();
Button();
Image();
groupButton();
frame.add(panel);
frame.setVisible(true);
}
public void MyPanel() {
panel = new JPanel();
panel.setLayout(null);}
public void RadioButtons() {
btLdap = new JRadioButton ("Ldap");
btLdap.setBounds(60,85,100,20);
panel.add(btLdap);
btKerbegos = new JRadioButton ("Kerbegos");
btKerbegos.setBounds(60,115,100,20);
panel.add(btKerbegos);
btSpnego =new JRadioButton("Spnego");
btSpnego.setBounds(60,145,100,20);
panel.add(btSpnego);
btSaml2 = new JRadioButton("Saml2");
btSaml2.setBounds(60,175,100,20);
panel.add(btSaml2);
}
public void Button() {
btNext = new JButton ("Next");
btNext.setBounds(400,260,100,20);
panel.add(btNext);
}
public void Image() {
ImageIcon image = new ImageIcon("image.jpg");
lblPicture = new JLabel(image);
lblPicture.setBounds(200,20, 330, 270);
panel.add(lblPicture);
}
private void groupButton() {
ButtonGroup bg1 = new ButtonGroup( );
bg1.add(btLdap);
bg1.add(btKerbegos);
bg1.add(btSpnego);
bg1.add(btSaml2);
}
}

To display another window, you would create the window, be it a JFrame, JDialog, or what have you, and call setVisible(true) just like you do for your first window.
You ask if your other "window" should be in another class, and likely that answer is yes. Since it will have a completely different set of behaviors and goals from the first class, better to separate out concerns.
Having said that, what you plan to do, to show multiple windows is not always the best user interface design. Better often is to show multiple views using a container that uses a CardLayout.
If you want to display another window in a modal fashion, that is, have the first window wait for the second window to be processed before allowing user interaction, the second window should be a modal JDialog or JOptionPane (a JDialog in disguise).

I think for what you want to achieve, the use of a CardLayout would be appropriate.
This enables you to have multiple panels within the one frame with only one panel visible at a time and has functionality to 'flip' through the panels like a 'deck of cards'. So on initialising your frame you create the panels you want, and specify which one to start at then your next button will go to the next panel in the list.
See the tutorial here there are also some video tutorials available on youtube.

Write the two GUI's in different classes. When you start your program, start the first GUI.
FirstGUI frame1 = new FirstGUI("Title text");
frame1.setVisible(true);
Then, in the action listener code for the button you call "next"...
frame1.setVisible(false); //if you want to save the frame
frame1.dispose(); //if you want to kill the frame
SecondGUI frame2 = new SecondGUI("Title text");
frame2.setVisible(true);

Java Swing: How can I implement a login screen before showing a JFrame?

I'm trying to make a little game that will first show the player a simple login screen where they can enter their name (I will need it later to store their game state info), let them pick a difficulty level etc, and will only show the main game screen once the player has clicked the play button. I'd also like to allow the player to navigate to a (hopefully for them rather large) trophy collection, likewise in what will appear to them to be a new screen.
So far I have a main game window with a grid layout and a game in it that works (Yay for me!). Now I want to add the above functionality.
How do I go about doing this? I don't think I want to go the multiple JFrame route as I only want one icon visible in the taskbar at a time (or would setting their visibility to false effect the icon too?) Do I instead make and destroy layouts or panels or something like that?
What are my options? How can I control what content is being displayed? Especially given my newbie skills?

A simple modal dialog such as a JDialog should work well here. The main GUI which will likely be a JFrame can be invisible when the dialog is called, and then set to visible (assuming that the log-on was successful) once the dialog completes. If the dialog is modal, you'll know exactly when the user has closed the dialog as the code will continue right after the line where you call setVisible(true) on the dialog. Note that the GUI held by a JDialog can be every bit as complex and rich as that held by a JFrame.
Another option is to use one GUI/JFrame but swap views (JPanels) in the main GUI via a CardLayout. This could work quite well and is easy to implement. Check out the CardLayout tutorial for more.
Oh, and welcome to stackoverflow.com!

Here is an example of a Login Dialog as #HovercraftFullOfEels suggested.
Username: stackoverflow Password: stackoverflow
import java.awt.*;
import java.awt.event.*;
import java.util.Arrays;
import javax.swing.*;
public class TestFrame extends JFrame {
private PassWordDialog passDialog;
public TestFrame() {
passDialog = new PassWordDialog(this, true);
passDialog.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new TestFrame();
frame.getContentPane().setBackground(Color.BLACK);
frame.setTitle("Logged In");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
}
});
}
}
class PassWordDialog extends JDialog {
private final JLabel jlblUsername = new JLabel("Username");
private final JLabel jlblPassword = new JLabel("Password");
private final JTextField jtfUsername = new JTextField(15);
private final JPasswordField jpfPassword = new JPasswordField();
private final JButton jbtOk = new JButton("Login");
private final JButton jbtCancel = new JButton("Cancel");
private final JLabel jlblStatus = new JLabel(" ");
public PassWordDialog() {
this(null, true);
}
public PassWordDialog(final JFrame parent, boolean modal) {
super(parent, modal);
JPanel p3 = new JPanel(new GridLayout(2, 1));
p3.add(jlblUsername);
p3.add(jlblPassword);
JPanel p4 = new JPanel(new GridLayout(2, 1));
p4.add(jtfUsername);
p4.add(jpfPassword);
JPanel p1 = new JPanel();
p1.add(p3);
p1.add(p4);
JPanel p2 = new JPanel();
p2.add(jbtOk);
p2.add(jbtCancel);
JPanel p5 = new JPanel(new BorderLayout());
p5.add(p2, BorderLayout.CENTER);
p5.add(jlblStatus, BorderLayout.NORTH);
jlblStatus.setForeground(Color.RED);
jlblStatus.setHorizontalAlignment(SwingConstants.CENTER);
setLayout(new BorderLayout());
add(p1, BorderLayout.CENTER);
add(p5, BorderLayout.SOUTH);
pack();
setLocationRelativeTo(null);
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
addWindowListener(new WindowAdapter() {
#Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
jbtOk.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (Arrays.equals("stackoverflow".toCharArray(), jpfPassword.getPassword())
&& "stackoverflow".equals(jtfUsername.getText())) {
parent.setVisible(true);
setVisible(false);
} else {
jlblStatus.setText("Invalid username or password");
}
}
});
jbtCancel.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
setVisible(false);
parent.dispose();
System.exit(0);
}
});
}
}

I suggest you insert the following code:
JFrame f = new JFrame();
JTextField text = new JTextField(15); //the 15 sets the size of the text field
JPanel p = new JPanel();
JButton b = new JButton("Login");
f.add(p); //so you can add more stuff to the JFrame
f.setSize(250,150);
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Insert that when you want to add the stuff in. Next we will add all the stuff to the JPanel:
p.add(text);
p.add(b);
Now we add the ActionListeners to make the JButtons to work:
b.addActionListener(this);
public void actionPerforemed(ActionEvent e)
{
//Get the text of the JTextField
String TEXT = text.getText();
}
Don't forget to import the following if you haven't already:
import java.awt.event*;
import java.awt.*; //Just in case we need it
import java.x.swing.*;
I hope everything i said makes sense, because sometimes i don't (especially when I'm talking coding/Java) All the importing (if you didn't know) goes at the top of your code.

Instead of adding the game directly to JFrame, you can add your content to JPanel (let's call it GamePanel) and add this panel to the frame. Do the same thing for login screen: add all content to JPanel (LoginPanel) and add it to frame. When your game will start, you should do the following:
Add LoginPanel to frame
Get user input and load it's details
Add GamePanel and destroy LoginPanel (since it will be quite fast to re-create new one, so you don't need to keep it memory).

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);