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Java -Repaint() not working when i want to call it

I wonder why the repiant() method is not working as intended. My Code:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JPanel;
public class RightPanel extends JPanel implements ActionListener{
JButton buttono;
JButton buttonu;
MyFrame frame;
ButtomPanel s;
public RightPanel(MyFrame frame){
super();
this.frame=frame;
s= new ButtomPanel(frame);
this.setPreferredSize(new Dimension((frame.getWidth()/3),frame.getHeight()));
setBackground(Color.green);
setLayout(new BorderLayout());
buttono = new JButton ("up");
buttonu = new JButton ("down");
buttono .addActionListener(this);
buttonu .addActionListener(this);
add(buttono , BorderLayout.NORTH);
add(buttonu , BorderLayout.SOUTH);
setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e) {
if (e.getSource()==buttono) {
System.out.println("Up");
s.x=s.x+10;
s.repaint();
}
}
I want to Repaint following class:
import java.awt.Color;
import java.util.Timer;
import java.util.TimerTask;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class ButtomPanel extends JPanel {
MyFrame frame;
BufferedImage image;
boolean geklickt=false;
public static int x=0;;
public ButtomPanel(MyFrame frame) {
super();
this.frame=frame;
this.setPreferredSize(new Dimension(((frame.getWidth()/3)*2),585));
setBackground(Color.blue);
java.net.URL resource = getClass().getResource("/resources/siegel.jpg");
try {
image = ImageIO.read(resource);
} catch (IOException e) {
e.printStackTrace();
}
setVisible(true);
}
public void paint(Graphics g) {
super.paint(g);
g.drawImage(image, 150+x, 150+x, 150, 150, null);}
}
}
I want to change with the ActionListener in the RightPanel Class the x from the BottomPanel Class and then repaint it, but it doesnt work. I can raise the x, but s.repaint() does not call the paint-Method.

s is never added to anything, so it will never be painted.
this.setPreferredSize(new Dimension((frame.getWidth()/3),frame.getHeight())); is a horribly bad idea. The window should be conforming to the size of the components, not the other way round. In fact, there's never really a good reason to expose MyFrame to the components this way, it provides these components control over MyFrame which they should never have.
java.net.URL resource = getClass().getResource("/resources/siegel.jpg");
try {
image = ImageIO.read(resource);
} catch (IOException e) {
e.printStackTrace();
}
is a bad idea. The class should be throwing the exception to those using it, so that they know something has gone wrong. Doing it this way not only consumes the error in a way which is difficult to trace, but also sets you up for a NullPointerException when you call g.drawImage(image, 150+x, 150+x, 150, 150, null)
Don't override paint
public void paint(Graphics g) {
super.paint(g);
g.drawImage(image, 150+x, 150+x, 150, 150, null);
}
prefer paintComponent instead. paint is actually a very complex method. See Painting in AWT and Swing and Performing Custom Painting for more details
public static int x=0; is a bad idea for a three reasons:
static is not your friend. What happens when you have more than one instance of ButtomPanel? Generally speaking, when you use static in this way, it's a red flag telling you that your design is wrong.
public is providing uncontrolled access to the property. This is generally discouraged and you could be preferring to use setters and getters to interact with the property.
JPanel already has a x property, which could make it confusing (ie if if someone used getX instead of x). Better to rename it to something like imageX of imageXOffset.
Runnable example...
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public final class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
JFrame frame = new JFrame();
frame.add(new RightPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
} catch (IOException ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
}
public class RightPanel extends JPanel implements ActionListener {
JButton buttono;
JButton buttonu;
ButtomPanel s;
public RightPanel() throws IOException {
super();
s = new ButtomPanel();
setBackground(Color.green);
setLayout(new BorderLayout());
buttono = new JButton("up");
buttonu = new JButton("down");
buttono.addActionListener(this);
buttonu.addActionListener(this);
add(buttono, BorderLayout.NORTH);
add(buttonu, BorderLayout.SOUTH);
add(s);
setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == buttono) {
System.out.println("Up");
s.addToImageXOffset(10);
}
}
}
public class ButtomPanel extends JPanel {
private BufferedImage image;
private int imageXOffset = 0;
public ButtomPanel() throws IOException {
super();
setBackground(Color.blue);
image = ImageIO.read(getClass().getResource("/images/Heart.png"));
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
public void addToImageXOffset(int delta) {
setImageXOffset(getImageXOffset() + delta);
}
public void setImageXOffset(int imageXOffset) {
this.imageXOffset = imageXOffset;
repaint();
}
public int getImageXOffset() {
return imageXOffset;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g); //To change body of generated methods, choose Tools | Templates.
g.drawImage(image, 150 + imageXOffset, 150 + imageXOffset, this);
}
}
}

Resizing BasicArrowButton

I'm trying to get a BasicArrowButton component to resize and can't get it to work for the life of me. The following code is a much simpler version of the problem, but still demonstrates what I'm trying to do. The button is in a JPanel with the panel's layout set to FlowLayout. It needs to resize while still remaining in the panel with the same layout. Thanks in advance, and sorry for bad formatting:
Main class:
package PackageMain;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.WindowConstants;
public class Main {
public static JFrame frame = new JFrame("Window");
public static PanelOne p1;
public static PanelTwo p2;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setBounds(100, 100, 800, 600);
p1 = new PanelOne();
frame.setVisible(true);
} catch(Exception e){
}
}
});
}
}
Second Class:
package PackageMain;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.JPanel;
import javax.swing.plaf.basic.BasicArrowButton;
public class PanelOne{
public PanelOne(){
FlowLayout fl = new FlowLayout();
BasicArrowButton b1 = new BasicArrowButton(BasicArrowButton.WEST);
JPanel p1 = new JPanel();
p1.add(b1);
p1.setLayout(fl);
b1.setPreferredSize(new Dimension(100, 100)); //DOESN'T WORK!
Main.frame.add(p1);
}
}

The problem is that the class BasicArrowButton overrides the method getPreferredSize(). So you either need to use layout, which does not honor this method, or provide your own implementation for this method.
First proposal:
import java.awt.Dimension;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import javax.swing.plaf.basic.BasicArrowButton;
public class BasicArrowButtonTest {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frm = new JFrame("Test arrow button");
JPanel p = new JPanel(new GridLayout(1, 1));
p.setPreferredSize(new Dimension(100, 100));
p.add(new BasicArrowButton(BasicArrowButton.WEST));
frm.add(p);
frm.pack();
frm.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frm.setLocationRelativeTo(null);
frm.setVisible(true);
}
});
}
}
Second proposal:
package org.swingsamples.label;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import javax.swing.plaf.basic.BasicArrowButton;
public class BasicArrowButtonTest {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frm = new JFrame("Test arrow button");
JPanel p = new JPanel(new FlowLayout());
BasicArrowButton btn = new BasicArrowButton(BasicArrowButton.WEST) {
#Override
public Dimension getPreferredSize() {
return new Dimension(100, 100);
}
};
p.add(btn);
frm.add(p);
frm.pack();
frm.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frm.setLocationRelativeTo(null);
frm.setVisible(true);
}
});
}
}

Problems with Graphics drawImage

I've been hunting through past StackOverflow posts and trying to figure out why my image won't display.
I know that the ImageIO is fine since I can run getWidth() on my BufferedImage and it returns the correct width.
Here is my Graphic class, followed by my main class.
(I'm sorry for trashy code, I'm new to this.)
Code in Graphic class:
package blackjack;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class Graphic extends JPanel implements ActionListener {
/**
*
*/
private static final long serialVersionUID = 1L;
public JFrame frame = new JFrame("Game Window");
public JPanel layout = new JPanel(new BorderLayout());
public JPanel menu = new JPanel();
public JPanel playing = new JPanel(new BorderLayout());
public JPanel game = new JPanel();
public BufferedImage cardArray[] = new BufferedImage[52];
public void begin() {
//starting menu
}
public void playersTurn() {
menu.add(playing);
Font font = new Font("",Font.PLAIN, 24);
JPanel btnHolder = new JPanel();
JLabel play = new JLabel("Playing:");
JLabel or = new JLabel(" or ");
JLabel question = new JLabel(" ? ");
question.setFont(font);
or.setFont(font);
play.setFont(font);
JButton hit = new JButton("Hit");
JButton stand = new JButton("Stand");
hit.addActionListener(this);
stand.addActionListener(this);
playing.add(play, BorderLayout.WEST);
playing.add(btnHolder, BorderLayout.CENTER);
btnHolder.add(hit);
btnHolder.add(or);
btnHolder.add(stand);
btnHolder.add(question);
}
public void gui() {
//main gui
Dimension imageD = new Dimension(71,96);
Dimension menuD = new Dimension(900,120);
menu.setBorder(BorderFactory.createLineBorder(Color.black));
menu.setPreferredSize(menuD);
JPanel titlePanel = new JPanel();
JLabel title = new JLabel("BlackJack");
title.setFont(new Font("", Font.PLAIN, 14));
titlePanel.add(title);
Graphic gr = new Graphic();
gr.setPreferredSize(imageD);
//adding
frame.add(layout);
layout.add(menu, BorderLayout.SOUTH);
layout.add(titlePanel, BorderLayout.NORTH);
layout.add(gr, BorderLayout.CENTER);
//frame settings
frame.setSize(900, 650);
frame.setResizable(false);
frame.setVisible(true);
}
public void buildPathArray() {
for(int i = 1; i<=52; i++){
BufferedImage im = null;
try {
im = ImageIO.read(new File(Blackjack.getInstallDir() + Blackjack.s + "src" + Blackjack.s + "cardpngs"+ Blackjack.s + (100+i)+".png"));
} catch (IOException e) {
e.printStackTrace();
}
cardArray[i-1]= im;
//System.out.println(Blackjack.getInstallDir() + "\\src\\cardpngs\\" + (100+i)+".png");
}
}
#Override
public void actionPerformed(ActionEvent e) {
if(e.getActionCommand().equals("Hit")) {
} else if(e.getActionCommand().equals("Stand")) {
}
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
//g.setColor(Color.GREEN);
//g.fillOval(20, 20, 20, 20);
g.drawImage(cardArray[0], 0, 0, this);
}
}
Code in my main class:
package blackjack;
import java.nio.file.Path;
import java.nio.file.Paths;
public class Blackjack {
public static String installDir = "";
public static String s = "";
public static void main(String[] args) {
Path currentRelativePath = Paths.get("");
installDir = currentRelativePath.toAbsolutePath().toString();
s = System.getProperty("file.separator");
Graphic gr = new Graphic();
gr.buildPathArray();
gr.gui();
//System.out.println(installDir);
//g.playersTurn();
}
public static String getInstallDir() {
return installDir;
}
}
The output is this:

You're creating one instance of Graphic in your Blackjack class...
public class Blackjack {
public static String installDir = "";
public static String s = "";
public static void main(String[] args) {
//...
Graphic gr = new Graphic();
gr.buildPathArray();
gr.gui();
}
And another in your Graphic class
public void gui() {
//...
Graphic gr = new Graphic();
gr.setPreferredSize(imageD);
//adding
//...
layout.add(gr, BorderLayout.CENTER);
//...
}
But you only initialise the images, using buildPathArray of the instance in you BlackBelt class, which is not what is actually displayed on the screen...
As a general rule of thumb, you shouldn't be creating an instance of JFrame from within another component with the express purpose of display that component. Your Graphic component is also trying to do too much. Instead, I would have a Game class, maybe, which pulled the title, menu and Graphic components together and then put that onto an instance of JFrame
The main reason for this is, is your Graphic class is trying to do too much. It should be solely responsible for display the cards and managing them. The Game class should manage the other UI elements and be responsible for ensuring that the UI meets the current state of the game "model", taking in user input (and listening to events from the other UI elements) and updating the model and responding to events that the model creates, a little more like...
BlackJack...
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class BlackJack {
public static void main(String[] args) {
new BlackJack();
}
public BlackJack() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new Game());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class Game extends JPanel {
private JPanel menu;
private Graphic graphic;
public Game() {
menu = new JPanel() {
#Override
public Dimension getPreferredSize() {
return new Dimension(900, 120);
}
};
menu.setBorder(BorderFactory.createLineBorder(Color.black));
JPanel titlePanel = new JPanel();
JLabel title = new JLabel("BlackJack");
title.setFont(new Font("", Font.PLAIN, 14));
titlePanel.add(title);
Graphic gr = new Graphic();
gr.buildPathArray();
setLayout(new BorderLayout());
add(menu, BorderLayout.SOUTH);
add(titlePanel, BorderLayout.NORTH);
add(gr, BorderLayout.CENTER);
}
}
}
Graphic...
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class Graphic extends JPanel {
private static final long serialVersionUID = 1L;
public BufferedImage cardArray[] = new BufferedImage[52];
public void begin() {
//starting menu
}
public void playersTurn() {
// All of this belongs in Game
}
#Override
public Dimension getPreferredSize() {
return new Dimension(71,96);
}
public void buildPathArray() {
for (int i = 1; i <= 52; i++) {
BufferedImage im = null;
try {
im = ImageIO.read(new File(Blackjack.getInstallDir() + Blackjack.s + "src" + Blackjack.s + "cardpngs" + Blackjack.s + (100 + i) + ".png"));
} catch (IOException e) {
e.printStackTrace();
}
cardArray[i - 1] = im;
//System.out.println(Blackjack.getInstallDir() + "\\src\\cardpngs\\" + (100+i)+".png");
}
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
//g.setColor(Color.GREEN);
//g.fillOval(20, 20, 20, 20);
g.drawImage(cardArray[0], 0, 0, this);
}
}
You might also want to have a look at Model-View-Controller.

JTabbedPane tab border removal

JTabbedPane - tab border is being shown even after using BasicTabbedPaneUI. Please let me know how can I change such that no border is shown between the tabs? Is there any method to remove the border completely ?
Please Send me the code snippet. Thanks in advance.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.SwingUtilities;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.plaf.basic.BasicTabbedPaneUI;
public class TabbedPaneTest implements Runnable {
#Override
public void run() {
final JTabbedPane pane = new JTabbedPane();
pane.addTab("A", createTab(Color.RED));
pane.addTab("B", createTab(Color.YELLOW));
pane.addTab("C", createTab(Color.BLUE));
pane.setUI(new BasicTabbedPaneUI() {
#Override
protected void paintContentBorder(Graphics g, int tabPlacement, int selectedIndex) {
}
});
pane.setBackground(Color.WHITE);
pane.addChangeListener(new ChangeListener() {
#Override
public void stateChanged(ChangeEvent arg0) {
pane.setForegroundAt(pane.getSelectedIndex(), Color.GREEN);
}
});
final JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(pane);
frame.pack();
//frame.setSize(500, 200);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private JPanel createTab(Color color) {
JPanel p = new JPanel(new BorderLayout()) {
private static final long serialVersionUID = 1L;
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 300);
}
};
p.setBorder(BorderFactory.createLineBorder(color, 2));
p.setBackground(Color.WHITE);
return p;
}
public static void main(String[] args) throws Exception {
SwingUtilities.invokeLater(new TabbedPaneTest());
}
}

// Remove the white line under a tab button
Insets insets = UIManager.getInsets("TabbedPane.contentBorderInsets");
insets.top = -1;
UIManager.put("TabbedPane.contentBorderInsets", insets);

CardLayout in Java change by action in one of the 'cards'

I am making a simple game using a JFrame. I have made a simple "Start" screen which basically consists of a String and a JButton. I am picking up the button click with the actionPerformed(ActionEvent e) method. I don't know how to change the cards using a button click. This may seem like a simple problem to solve, but the twist comes with this: My main JFrame, my StartScreen and my JPanel where the game takes place are all in separate files. My main file, Virus.java, is where I create the JFrame. My file VirusGamePanel.java is where the game takes place. My file StartScreen.java is the screen with the button. I want to change 'cards' to the game screen when the player clicks the button. How can I do this?
My StartScreen.java file:
package virus;
import javax.swing.JPanel;
import java.awt.event.ActionListener;
import java.awt.Graphics;
import java.awt.Font;
import java.awt.Color;
import javax.swing.JButton;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.CardLayout;
public class StartScreen extends JPanel implements ActionListener{
private static final long serialVersionUID = 1L;
JButton start = new JButton("Start");
public StartScreen(){
start.addActionListener(this);
start.setBounds(new Rectangle(400,300,100,30));
this.add(start);
}
public void paint(Graphics g){
super.paint(g);
g.setFont(new Font("Impact",Font.BOLD,72));
g.setColor(Color.MAGENTA);
g.drawString("Virus",275,300);
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==start)
{
//what to do here?
}
}
}
My Virus.java file:
package virus;
import javax.swing.*;
import java.awt.CardLayout;
import virus.StartScreen;
public class Virus extends JFrame{
private static final long serialVersionUID =1L;
JFrame jf = new JFrame("Virus");
static JPanel thegame = new JPanel(new CardLayout());
JPanel game = new VirusGamePanel();
JPanel start = new StartScreen();
public Virus(){
jf.setResizable(false);
jf.setSize(600,600);
jf.setLocationRelativeTo(null);
jf.setDefaultCloseOperation(EXIT_ON_CLOSE);
jf.setVisible(true);
jf.add(thegame);
thegame.add(start);
thegame.add(game);
}
public static void main(String[] args) {
new Virus();
}
}

You simply have to right this in your actionPerformed(...) method :
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==start)
{
//what to do here?
CardLayout cardLayout = (CardLayout) Virus.thegame.getLayout();
cardLayout.next(Virus.thegame);
}
}
As very much pointed out by #kleopatra (THE EMPRESS) herself, don't override paint() instead do your painting stuff inside paintComponent(Graphics g) method of any JPanel/JComponent. Moreover, first add the components to your JFrame, once it's size is realized, then only set it to Visible, not before that. Instead of setting sizes for the JFrame simply override the JPanel's method getPreferredSize(), make it return some valid Dimension Object.
Do watch this sequence, as you write your code the next time :
public Virus(){
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.setResizable(false);
thegame.add(start);
thegame.add(game);
jf.add(thegame);
jf.pack();
jf.setLocationRelativeTo(null);
jf.setVisible(true);
}
Here is your full code :
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.event.ActionListener;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Font;
import java.awt.Color;
import javax.swing.JButton;
import javax.swing.JLabel;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.CardLayout;
public class Virus extends JFrame{
private static final long serialVersionUID =1L;
JFrame jf = new JFrame("Virus");
static JPanel thegame = new JPanel(new CardLayout());
JPanel game = new VirusGamePanel();
JPanel start = new StartScreen();
public Virus(){
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.setResizable(false);
thegame.add(start);
thegame.add(game);
jf.add(thegame);
jf.pack();
jf.setLocationRelativeTo(null);
jf.setVisible(true);
}
public static void main(String[] args) {
new Virus();
}
}
class StartScreen extends JPanel implements ActionListener{
private static final long serialVersionUID = 1L;
JButton start = new JButton("Start");
public StartScreen(){
start.addActionListener(this);
start.setBounds(new Rectangle(400,300,100,30));
this.add(start);
}
#Override
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.setFont(new Font("Impact",Font.BOLD,72));
g.setColor(Color.MAGENTA);
g.drawString("Virus",275,300);
}
#Override
public Dimension getPreferredSize()
{
return (new Dimension(600, 600));
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==start)
{
//what to do here?
CardLayout cardLayout = (CardLayout) Virus.thegame.getLayout();
cardLayout.next(Virus.thegame);
}
}
}
class VirusGamePanel extends JPanel
{
public VirusGamePanel()
{
JLabel label = new JLabel("I am ON", JLabel.CENTER);
add(label);
}
#Override
public Dimension getPreferredSize()
{
return (new Dimension(600, 600));
}
}

Your StartScreen class has to have access to the instance of the CardLayout of the JFrame and the instance of the VirusGamePanel class. You can pass these instances in the constructor or a setLayout method and setVirusGamePanel method of your StartScreen class.
Something like:
layout.next(virusGamePanel);
should work.