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Update JLabel text

I'm working on a simple GUI. On Button press i want to increase/decrease a variable and update the corresponding JLabel.
class JFrameSetUp
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JFrameSetUp extends JFrame implements ActionListener {
private int RecHeight = 0;
private int RecWidth = 0;
//Here Buttons
JButton HeightIncrease = new JButton("+");
JButton HeightDecrease = new JButton("-");
JLabel height = new JLabel(Integer.toString(RecHeight));
JLabel width = new JLabel(Integer.toString(RecWidth));
GridLayout gridLayout = new GridLayout(2, 4);
public JFrameSetUp(){
}
public void addComponentsToPane(final Container pane){
//Create GridPanel and set Layout
JPanel grid = new JPanel();
grid.setLayout(gridLayout);
//Create buttondrawPanel and set Layout
JPanel buttondraw = new JPanel();
buttondraw.setLayout(new GridLayout(2, 0));
//Adding Components to GridPanel
//Adding Layouts to pane
pane.add(grid, BorderLayout.NORTH);
pane.add(new JSeparator(), BorderLayout.CENTER);
pane.add(buttondraw, BorderLayout.SOUTH);
}
#Override
public void actionPerformed(ActionEvent e) {
//Setting up ActionListener to Buttons
if (e.getSource() == this.HeightDecrease) {
RecHeight -= 1;
height.setText(Integer.toString(RecHeight));
} else if (e.getSource() == this.HeightIncrease) {
RecHeight += 1;
height.setText(Integer.toString(RecHeight));
}
}
}
Class with MainMethod
import javax.swing.JFrame;
public class Program {
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
//Create and set up the window.
JFrameSetUp frame = new JFrameSetUp();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Set up the content pane.
frame.addComponentsToPane(frame.getContentPane());
//Display the window.
frame.pack();
frame.setVisible(true);
}
}
I'm aware, that's kind a newbish question. I think I'm wrong with my Code Structure. Any help is appreciated.
Thanks in advance.

You never register any ActionListeners to the buttons...
HeightIncrease.addActionListener(this);
HeightDecrease.addActionListener(this);
You also never add the buttons to the GUI
buttondraw.add(HeightIncrease);
buttondraw.add(HeightDecrease);
You also never add the labels to the GUI either...
grid.add(height);
grid.add(width);
I reworked the code, because your example was messing with my mind, hope you don't mind...
It's conceptually the same idea, just done slightly more efficently
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSeparator;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
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 TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private int recHeight = 0;
private int recWidth = 0;
//Here Buttons
JButton heightIncrease = new JButton("+");
JButton heightDecrease = new JButton("-");
JLabel height = new JLabel(Integer.toString(recHeight));
JLabel width = new JLabel(Integer.toString(recWidth));
GridLayout gridLayout = new GridLayout(2, 4);
public TestPane() {
setLayout(new BorderLayout());
//Create GridPanel and set Layout
JPanel grid = new JPanel();
grid.setLayout(gridLayout);
grid.add(height);
grid.add(width);
//Create buttondrawPanel and set Layout
JPanel buttondraw = new JPanel();
buttondraw.setLayout(new GridLayout(2, 0));
heightIncrease.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
recHeight += 1;
height.setText(Integer.toString(recHeight));
}
});
heightDecrease.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
recHeight -= 1;
height.setText(Integer.toString(recHeight));
}
});
buttondraw.add(heightIncrease);
buttondraw.add(heightDecrease);
//Adding Components to GridPanel
//Adding Layouts to pane
add(grid, BorderLayout.NORTH);
add(new JSeparator(), BorderLayout.CENTER);
add(buttondraw, BorderLayout.SOUTH);
}
}
}
I would encourage you to spend some time having a look at How to Use Buttons, Check Boxes, and Radio Buttons and How to Write an Action Listeners for more details

After changing the value call
frame.repaint();

Good to see you learning Java! A few things I should point out.
Firstly, your variable names are good, but they don't follow the Java naming convention. Even though it seems small, it's just good practice to follow.
Of course, your actual problem; the action listener you've implemented is on the JFrame. (See how you extend JFrame and implement ActionListener?) This ActionListener should be on the button. You'll can do this a few ways.
Method 1: By adding it inline with your code
JButton heightButton = new JButton("Increase Height");
heightButton.addActionListener(new ActionListener(){
#Override
public void run(){
//run method here
}
});
Method 2: Create a class which implements ActionListener
class ButtonListener implements ActionListener{
#Override
public void run(){
//actionListener code here
}
}
And then instantiate an object of this type and add it directly to your code.
ActionListner buttonListener = new ButtonListener(); //or ButtonListener buttonListener = new ButtonListener();
JButton heightButton = new JButton("Increase Height");
heightButton.addActionListener(buttonListener);
Of course, as in MadProgrammers answer, don't forget to add the labels and such to your JFrame or JPanel. Good luck learning Java!

I bet that your program just shows nothing, isn't it? That's because in addComponentsToPane method, you didn't add any component but empty JPanels. After the comment //Adding Components to GridPanel, you should:
buttondraw.add(HeightIncrease);
buttondraw.add(HeightDecrease);
grid.add(height);
grid.add(width);
Then, to listen to button event, you should also add :
HeightIncrease.addActionListener(this);
HeightDecrease.addActionListener(this);
"this" is because your frame JFrameSetUp implements ActionListener, so when either bootton is clicked the method actionPerformed is invoked.
As JLabel.setText method will repaint itself and consequently its component hierarchi is repainted as well, you haven't to do anything othr.

I'm trying to draw a string in JFrame, but it won't work.. Help please

I'm trying to display a string when a button is pressed, but it does not work. I do not know what the problem is. I get no error, but that does not bother me. I'm missing something fundamental, I suppose. Please help!!
//I'm trying to draw a string in the frame when a button is pressed, but it won't work..
//Can't figure out what the problem is.
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class AppletTwo extends JFrame implements ActionListener
{
JFrame frameOne;
JButton btnOne;
AppletTwo()
{
frameOne = new JFrame("frameOne");
frameOne.setSize(320,240);
frameOne.setLayout(new FlowLayout(FlowLayout.LEFT));
frameOne.setVisible(true);
frameOne.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
btnOne = new JButton("Print");
btnOne.addActionListener(this);
frameOne.add(btnOne);
}
public void actionPerformed(ActionEvent ae)
{
if(ae.getSource() == btnOne)
{
repaint();
}
}
public void paint(Graphics g)
{
g.drawString("Never Works",150,150);
}
public static void main(String[] args)
{
AppletTwo frame1 = new AppletTwo();
}
}

" I'm missing something fundamental, I suppose. "
Yes, you are:
Main problem:
Your class is JFrame which is the component for which you are overriding the paint method. But you create another instance of a JFrame, which is the one you setVisible to. Keep in mind, you haven't drawn anything to this frame. So you are seeing the new instance of frame, not the class frame for which you are painting (and for which you never set visible).
Other problems:
You should always call super.paint[Component] after a paint[Component] override
#Override
public void paint(Graphics g) {
super.paint(g);
}
Don't paint on top level container like JFrame. Instead paint on a JPanel or JComponent and override is paintComponent method and call super.paintComponent, then add that component to the frame. See Performing Custom Painting
Swing apps should be run on the event dispatch thread (EDT). You can do so by wrapping your main code in a SwingUtilities.invokeLater(...). See Initial Threads
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable(){
public void run() {
AppletTwo frame1 = new AppletTwo();
}
});
}
Generally, you always want to set the frame visible after adding your components.
Other notes:
See Extends JFrame vs. creating it inside the the program
UPDATE
Example with all the above mentioned points.
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
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.JTextField;
import javax.swing.SwingUtilities;
public class SimpleDrawing {
public SimpleDrawing() {
final DrawingPanel panel = new DrawingPanel();
final JTextField field = new JTextField(15);
JButton button = new JButton("Change name");
button.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
String someString = field.getText();
if (!someString.isEmpty()) {
panel.setString(someString);
}
}
});
JPanel bottomPanel = new JPanel();
bottomPanel.add(field);
bottomPanel.add(button);
JFrame frame = new JFrame();
frame.add(panel);
frame.add(bottomPanel, BorderLayout.SOUTH);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public class DrawingPanel extends JPanel {
private String someString = "Stackoverflow";
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString(someString, 75, 75);
}
#Override
public Dimension getPreferredSize() {
return new Dimension (300, 100);
}
public void setString(String someString) {
this.someString = someString;
repaint();
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run() {
new SimpleDrawing();
}
});
}
}

CardLayout with MouseListener not working

I am dealing with CardLayout. The JPanel I added as a contentpane to my JFrame has a CardLayout, and I want to swap between different panes. I have a working pane with buttons and five other image panes for the tutorial that are to be displayed only if a certain boolean value is true. I mean, every time this boolean is set true, five swaps should be done using next() method. My problem is that, after the first swap, the screen becomes blank. why does this happen?
Second question. I am using a MouseListener to swap, but I would like the program to do it automatically after some time. I tried to use Thread.sleep(5000), but I get a black screen.
This is my code, where card is a class variable in order to use it in the Mouselistener, parent is the working panel, already created, and ImagePanel is a class to create tutorialPanels, which adds to them the MouseListener below. Also, rootPane is a class pane.
card = new CardLayout();
rootPane = new JPanel(card);
this.getContentPane().add(rootPane);
//create panels to add
ImagePanel inputTutorial = new ImagePanel("backgroundIn.png");
ImagePanel numericTutorial = new ImagePanel("backgroundNum");
ImagePanel outputTutorial = new ImagePanel("backgroundOut");
ImagePanel commandTutorial = new ImagePanel("backgroundCom");
ImagePanel errorTutorial = new ImagePanel("backgroundErr");
ImagePanel finalTutorial = new ImagePanel("backgroundFinal");
//add the panels
rootPane.add(parent);
rootPane.add(inputTutorial);
rootPane.add(numericTutorial);
rootPane.add(outputTutorial);
rootPane.add(commandTutorial);
rootPane.add(errorTutorial);
rootPane.add(finalTutorial);
//set rootPane content panel
this.getContentPane().add(rootPane);
//if the boolean is true
if (firstTime == true) {
card.next(rootPane);
//other swaps done by mouselisteners
}
This is the mouselistener:
//mouse click listener
private class MouseActionListener implements MouseListener {
public void mousePressed (MouseEvent e) {
}
#Override
public void mouseClicked(MouseEvent arg0) {
card.next(rootPane);
}
#Override
public void mouseEntered(MouseEvent arg0) {
}
#Override
public void mouseExited(MouseEvent arg0) {
}
#Override
public void mouseReleased(MouseEvent arg0) {
}
}
I know that the listener is executed because I checked it.
Any help would be appreciated, thank you in advance.

"but I would like the program to do it automatically after some time. I tried to use Thread.sleep(5000)"
Don't use Thread.sleep. Instead use a javax.swing.Timer. You can learn more at How to Use Swing Timers
Here's a simple example, using some of your app format.
import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class SlideShow {
public SlideShow() {
final CardLayout layout = new CardLayout();
final JPanel mainPanel = createMainPanel(layout);
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
layout.next(mainPanel);
}
});
timer.start();
JFrame frame = new JFrame();
frame.add(mainPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private JPanel createMainPanel(CardLayout layout) {
JPanel panel = new JPanel(layout);
panel.add(new ImagePanel("mario.png"));
panel.add(new ImagePanel("bowser.png"));
panel.add(new ImagePanel("luigi.png"));
panel.add(new ImagePanel("koopa.png"));
panel.add(new ImagePanel("princess.png"));
return panel;
}
private class ImagePanel extends JPanel {
BufferedImage image;
public ImagePanel(String fileName) {
try {
image = ImageIO.read(getClass().getResource("/marioblobs/" + fileName));
} catch (IOException ex) {
ex.printStackTrace();
}
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image, 0, 0, this);
}
#Override
public Dimension getPreferredSize() {
return image == null ? new Dimension(200, 200)
: new Dimension(image.getWidth(), image.getHeight());
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new SlideShow();
}
});
}
}

Giving a JPanel priority focus

I have a JPanel that is using a KeyListener as the content pane as the window; however, there are buttons and text fields in a grid layout on top of the JPanel.
How do I prioritize the focus of the JPanel that it retains focus after editing text or clicking the buttons so I can read the key input?

You just need to add a FocusListener on the focusLost event and then request focus back again. Something like this:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JPanelFocus {
public static void main(String... argv) throws Exception {
EventQueue.invokeLater(new Runnable() {
public void run() {
JFrame f = new JFrame("FocusTest");
JButton b = new JButton("Button");
final JPanel p = new JPanel();
p.add(b);
// Here is the KeyListener installed on our JPanel
p.addKeyListener(new KeyAdapter() {
public void keyTyped(KeyEvent ev) {
System.out.println(ev.getKeyChar());
}
});
// This is the bit that does the magic - make sure
// that our JPanel is always focussed
p.addFocusListener(new FocusAdapter() {
public void focusLost(FocusEvent ev) {
p.requestFocus();
}
});
f.getContentPane().add(p);
f.pack();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
// Make sure JPanel starts with the focus
p.requestFocus();
}
});
}
}
This won't work if you have fields that need to keep the focus though (you mentioned an editable text field). When should key events go to the text field and when should they go to the JPanel?

As an alternative, you could also just make the child components non-focusable.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class MyPanel extends JPanel implements KeyListener {
public MyPanel() {
this.setFocusable(true);
this.addKeyListener(this);
// for each component
JComboBox<String> comboBox = new JComboBox<String>();
comboBox.addItem("Item1");
this.add(comboBox);
// this is what keeps each child from intercepting KeyEvents
comboBox.setFocusable(false);
}
public void keyPressed(KeyEvent e) { ... }
public void keyTyped(KeyEvent e) { ... }
public void keyReleased(KeyEvent e) { ... }
public static void main(String[] args) {
// create a frame
JFrame frame = new JFrame();
frame.setSize(640, 480);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// add MyPanel to frame
MyPanel panel = new MyPanel();
frame.add(panel);
frame.setVisible(true);
}
}

Java event propagation stopped

I have a main window:
public class MainPanel extends JFrame implements MouseListener {
public MainPanel() {
setLayout(new FlowLayout());
setDefaultCloseOperation(EXIT_ON_CLOSE);
addMouseListener(this);
ChildPanel child = new ChildPanel();
add(child);
JPanel spacer = new JPanel();
spacer.setPreferredSize(new Dimension(50, 50));
add(spacer);
pack();
setLocationRelativeTo(null);
}
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("Mouse click event on MainPanel");
}
}
And a child JPanel:
public class ChildPanel extends JPanel implements MouseListener {
public ChildPanel() {
setBackground(Color.RED);
setPreferredSize(new Dimension(200, 200));
//addMouseListener(this);
}
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("Mouse click event on ChildPanel");
}
}
With the call to addMouseListener commented out in the child panel, the parent receives click events when I click anywhere in the window, including on the child. If I uncomment that call and click on the child panel, only the child receives the click event and it doesn't propagate to the parent.
How do I stop the event from being consumed by the child?

In Swing, you generally want the clicked component to respond; but you can forward the mouse event to the parent, as shown below. Here's a related example.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
/** #see https://stackoverflow.com/questions/3605086 */
public class ParentPanel extends JPanel {
public ParentPanel() {
this.setPreferredSize(new Dimension(640, 480));
this.setBackground(Color.cyan);
this.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("Mouse clicked in parent panel.");
}
});
JPanel child = new JPanel();
child.setPreferredSize(new Dimension(320, 240));
child.setBackground(Color.blue);
child.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("Mouse clicked in child panel.");
ParentPanel.this.processMouseEvent(e);
}
});
this.add(child);
}
private void display() {
JFrame f = new JFrame("MouseEventTest");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(this);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
new ParentPanel().display();
}
});
}
}

I don't think you can. I believe it's a Swing design principle that only one component receives an event.
You can get the behavior you want, however, but pass the JFrame to the ChildPanel and calling its mouseClicked(MouseEvent) or whatever method you want. Or just get the parent component.
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("Mouse click event on ChildPanel");
this.frame.mouseClicked(e);
getParent().mouseClicked(e);
}