I am new to Java. I am trying to make text appear on a JLabel after a virtual button is clicked. However, I can't seem to find a solution to this. When I use the if statement it won't work. How can I make the text appear after the button was pressed?
import java.awt.event.*;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.JPanel;
import java.awt.Graphics;
public class autos extends JLabel implements ActionListener
{
private static final long serialVersionUID = 1L;
int now=0;
public autos(){
JLabel l=new JLabel("");
JFrame f=new JFrame("the title");
JPanel p=new JPanel();
JButton b=new JButton("click");
f.setBounds(400,500,400,500);
f.setVisible(true);
p.add(b);
f.add(p);
b.addActionListener(this);
p.setVisible(true);
p.add(l);
f.add(l);
if(now==1)
{
l.setText("hello");
l.setOpaque(true);
}
p.setBounds(200,200,200,200);
l.setBounds(100,100,100,100);
l.setOpaque(true);
f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.drawRect(200,300,89,90);
g.drawString("buv",80,80);
repaint();
}
public static void main(String[] args)
{
new autos();
}
#Override
public void actionPerformed(ActionEvent e) {
now=1;
System.out.println("worked");
System.out.println(now);
}
}
You are setting up your label in your constructor code, which executes before the event handler which sets the now variable to 1.
What you can do is to move this code:
l.setText("hello");
l.setOpaque(true);
To here:
#Override
public void actionPerformed(ActionEvent e) {
now=1;
System.out.println("worked");
System.out.println(now);
l.setText("hello");
l.setOpaque(true);
}
This is a minimally working example of updating the text on button click. See the comments in code for the variety of changes.
import java.awt.event.*;
import javax.swing.*;
/* There is no need to extend label here. */
// public class autos extends JLabel implements ActionListener
public class autos implements ActionListener {
private static final long serialVersionUID = 1L;
int now = 0;
// this is now a class attribute, accessible to any method of this class.
JLabel l;
public autos() {
// this no longer declares a local variable, but instead
// creates an instance of the class attribute.
l = new JLabel("");
JFrame f = new JFrame("the title");
JPanel p = new JPanel();
JButton b = new JButton("click");
f.setBounds(400, 500, 400, 500); // this needs fixing!
f.setVisible(true);
p.add(b);
f.add(p);
b.addActionListener(this);
p.setVisible(true);
p.add(l);
f.add(l);
p.setBounds(200, 200, 200, 200); // this needs fixing!
l.setBounds(100, 100, 100, 100); // this needs fixing!
l.setOpaque(true);
f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
}
/* I cannot tell what this was trying to achieve, but whatever it was,
this was the wrong way to go about it. Never call repaint() from within
the paintComponent method as this creates an infinite loop! */
/*
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawRect(200, 300, 89, 90);
g.drawString("buv", 80, 80);
repaint();
}
*/
public static void main(String[] args) {
// Swing GUIs should be created and updated on the EDT
new autos();
}
#Override
public void actionPerformed(ActionEvent e) {
/* This logic is questionable, but it denpends on what you are trying
to achieve here, something I'm not clear on. */
now = 1;
if (now == 1) {
l.setText("hello");
l.setOpaque(true);
}
System.out.println("worked");
System.out.println(now);
}
}
Edit
You added two comments at the setBounds part saying this needs fixing!. There I tried to resize the JPanel and JLabel but it's obvious it doesn't work.
How should I proceed here?
Here are some 'copy/paste comments' I regularly use:
Java GUIs have to work on different OS', screen size, screen resolution etc. using different PLAFs in different locales. As such, they are not conducive to pixel perfect layout. Instead use layout managers, or combinations of them along with layout padding and borders for white space.
See Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing? (Yes.)
Provide ASCII art or a simple drawing of the intended layout of the GUI at minimum size, and if resizable, with more width and height.
Now, to expand on those comments for this use-case:
That is advice I offer for people trying to make a null layout, but it also applies here.
This is relevant because there is one component (the custom painted one, if it exists) that needs to #Override the getPreferredSize(..) method to return a size as a suggestion to the layout managers or for packing the top level container.
The 3rd comment is because it is hard to advise how to code this GUI without knowing the end effect that is required.
Of course, I should point out: Each SO thread is expected to be a single, specific question. I really should have told you to start a new question on the other matters, but let it slide for this edit.
Related
I'm trying to draw a line in a JFrame, but line isn't drawn.
I tried to use the method setOpaque(true) for contentPane, lblNewLabel and l but nothing changed. I also tried call repaint(); outside this class but the situation is still the same. Here's the code:
public class DrawingClass extends JFrame
{
private JPanel contentPane;
public DrawingClass(int n, int s, int p) {
Line l= new Line();
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
setBounds(700, 300, 480, 640);
contentPane = new JPanel();
contentPane.setOpaque(true);
setResizable(false);
setContentPane(contentPane);
contentPane.setLayout(null);
JLabel lblNewLabel = new JLabel("");
lblNewLabel.setIcon(new ImageIcon("image.png"));
lblNewLabel.setBounds(0, 0, 480, 640);
contentPane.add(lblNewLabel);
l.setBounds(0,0,480,640);
contentPane.add(l);
repaint();
}
class Line extends JPanel
{
public void paintComponent(Graphics g) {
g.setColor(Color.BLUE);
g.fillRect(10, 10, 15, 12);
}
}
}
I expect a little line on the top left of the JFrame, above the background wallpaper, but nothing happen. It shows only the wallpaper.
There are several errors in your code:
You're extending JFrame but you're not changing its behavior, so why are you doing that? JFrame is a rigid component, so it's never a good idea to extend from it, build your GUI based on JPanels instead. See: Extends JFrame vs. creating it inside the program
Don't explicitly set the size of the JFrame, call pack() on it and instead override getPreferredSize from the JPanel, see: Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?
You don't need to call setOpaque(...) in this case.
Don't use a null-layout, it might lead to strange errors, because null Layout is Evil and frowned upon
We don't have access to your image so we cannot test the ImageIcon and it's also not related to your question. However you should load your images as resources
Don't explicitly set the bounds of each element, this is related to point (4) and you should use a Layout Manager or combinations of them to get your desired GUI.
Don't call repaint() that way, it has no effect, it is supposed to repaint your UI when there's a change in it. However there is no change at the start of your program.
You're breaking the paint-chain by not calling super.paintComponent(...) inside your paintComponent(...) method. Check the Tutorial on Custom Painting in Swing so that you learn how to do it properly
And be careful, as paintComponents(...) (With a trailing s) is different from paintComponent(...) (Look at your title)
So, after doing all of the above changes, we get to this simple program:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class DrawingClass {
private JPanel contentPane;
private JFrame frame;
public static void main(String args[]) {
SwingUtilities.invokeLater(() -> new DrawingClass().createAndShowGUI());
}
public void createAndShowGUI() {
frame = new JFrame(getClass().getSimpleName());
Line line = new Line();
frame.add(line);
frame.setResizable(false);
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
class Line extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLUE);
g.fillRect(10, 10, 15, 12);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(480, 640);
}
}
}
Which produces the following output:
I have been struggling with this for some time. At first, I only used ActionListener, then I added the paintComponent, but I have no idea what to put there. I read some tutorials and used their code as an example, but it still doesn't work. Right now, the end result is the same as it was without PaintComponent.
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class Scream extends JPanel {
private JButton button = new JButton("OK");
private Color screenColor;
private JPanel panel = new JPanel();
private JFrame frame;
private Dimension screenSize;
private ImageIcon image;
private JLabel label = new JLabel(image);
private int x;
private int y;
private boolean mouseClicked;
public Scream() {
button.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent e ) {
if (e.getSource() == button) {
mouseClicked = true;
frame.getContentPane().add(label);
frame.setSize(image.getIconWidth(), image.getIconHeight());
panel.repaint();
}
}
});
frame = new JFrame ("Existential angst");
screenColor = new Color(150, 100, 0);
panel.setBackground( screenColor );
frame.add(button, BorderLayout.PAGE_END);
frame.add(panel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(1300, 700);
frame.setVisible(true);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
image.paintComponent(this, g, 1300, 700);
}
public static void main (String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
Scream scream = new Scream();
}
});
}
}
If you are trying to dynamically add an image to a panel then you need to add the label to the panel. There is no need for any custom painting.
The basic code for adding components to a visible GUI is:
panel.add(...);
panel.revalidate();
panel.repaint();
Also, don't attempt to set the size of the frame to the size of the image. A frame contains a titlebar and borders. Instead you can use frame.pack();
I noticed a couple of issues:
image is never initialized to anything so it is null, effectively making the label empty. I assume maybe your example was just incomplete?
Once I initialized the image to something, your example still did not work. Turns out adding label without specifying any constraint basically does nothing (I assume since adding a component to a border layout without a constraint puts it in the center where panel already is). When I added the label to BorderLayout.NORTH, everything worked (though resizing the frame to the size of the image makes it only partially visible since the frame includes the OK button)
I want to put my background image at the very bottom in this frame, and the button on top. However the code I wrote below doesn't work. Can anyone see where the problems are?
Another thing is that even though I set the location for my button, it keep showing at the top center on the frame.
Please ignore the comment lines. (I was just guessing, and hoping them will work, but they don't apparently.)
public class Menu extends JFrame{
private JLayeredPane pane;
private JLayeredPane pane2;
public Menu(){
final JFrame f = new JFrame("Chinese Chess");
JButton play = new JButton("Play vs. AI");
f.setLayout(new FlowLayout());
f.setLocationRelativeTo(null);
f.setSize(800, 800);
f.setVisible(true);
f.setResizable(false);
//f.pack();
pane = new JLayeredPane();
pane2 = new JLayeredPane();
f.add(pane);
f.add(pane2);
//background image
JLabel background = new JLabel(new ImageIcon("res/img/background.png"));
background.setLocation(0, 0);
background.setSize(800, 800);
pane.add(background, JLayeredPane.FRAME_CONTENT_LAYER);
pane2.add(play, JLayeredPane.DEFAULT_LAYER);
//pane.moveToBack();
//button PlayAI
play.setLocation(500,500);
play.setPreferredSize(new Dimension(100,50));
//f.setLayout(new FlowLayout());
//frame menu
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//f.getContentPane().add(play);
play.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
new PlayAI();
}
});
}
public static void main(String[] args){
new Menu();
}
Problems/Solutions:
setLocation(...) and setBounds(...) types of calls are ignored by most layout managers. The only way to use them is to set the layout of the container to null via .setLayout(null);
But having said that, while null layouts and setBounds() 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.
So in sum -- don't do this, don't use null layouts or setBounds, but rather nest JPanels, each using its own layout manager, and thereby create easy to maintain and decent GUI's.
If you want an image to be in the background, then draw it in a JPanel that you use as a container for your GUI components by drawing it in the JPanel's paintComponent(Graphics g) method as has been demonstrated in many many similar questions on this site -- I'll find you some of mine in a second.
If you add any JPanels on top of this image drawing JPanel, be sure that you can see through them by calling setOpaque(false) on these overlying JPanels. Otherwise you'll cover up the image.
Your code has two JFrames when only one is needed. Get rid of the one you don't use.
You call setVisible(true) too early on the JFrame, before components have been added to the GUI -- don't. Call it only after adding everything to the GUI so all display OK.
You're creating two JLayedPanes, and completely covering one by the other by adding them to the JFrame without understanding how the JFrame's BorderLayout handles added components.
I suggest that you not even use one JLayeredPane but instead draw in the JPanel as noted above, and use that as your container.
Your code looks to be opening a completely new GUI window when the play button is pressed, and if so, this can get annoying to the user fast. Consider swapping views instead with a CardLayout.
For example:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.*;
// extend JPanel so you can draw to its background
#SuppressWarnings("serial")
public class Menu2 extends JPanel {
private BufferedImage bgImage = null; // our background image
private JButton playButton = new JButton(new PlayVsAiAction("Play Vs. AI", KeyEvent.VK_P));
public Menu2(BufferedImage bgImage) {
this.bgImage = bgImage;
setLayout(new GridBagLayout()); // center our button
add(playButton);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (bgImage != null) {
g.drawImage(bgImage, 0, 0, this);
}
}
// to size our GUI to match a constant or the image.
#Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
// if you want to size it based on the image
if (bgImage != null) {
int width = bgImage.getWidth();
int height = bgImage.getHeight();
return new Dimension(width, height);
} else {
return super.getPreferredSize();
}
// if you want to size the GUI with constants:
// return new Dimension(PREF_W, PREF_H);
}
private class PlayVsAiAction extends AbstractAction {
public PlayVsAiAction(String name, int mnemonic) {
super(name); // have our button display this name
putValue(MNEMONIC_KEY, mnemonic); // alt-key to press button
}
#Override
public void actionPerformed(ActionEvent e) {
// TODO code to start program
}
}
private static void createAndShowGui() {
BufferedImage img = null;
String imagePath = "res/img/background.png";
try {
// TODO: fix this -- use class resources to get image, not File
img = ImageIO.read(new File(imagePath));
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
Menu2 mainPanel = new Menu2(img);
JFrame frame = new JFrame("Chinese Chess");
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(() -> {
createAndShowGui();
});
}
}
Apart from the solution above... you should create and launch your swing application this way:
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
// Instantiate your JFrame and show it
}
I am trying to draw on my JFrame, but I can't get my super.paintComponents(g); to work. Also, nothing is drawing on my JFrame when I tell it to in my paintComponent() method.
Here is the code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class MTGSAMPServerReference extends JFrame implements ActionListener {
public static Toolkit tk = Toolkit.getDefaultToolkit();
static int ScrnWidth = ((int) tk.getScreenSize().getWidth());
static int ScrnHeight = ((int) tk.getScreenSize().getHeight());
private static final long serialVersionUID = 1L;
private static JList list1;
private static JButton next;
public MTGSAMPServerReference() {
// set flow layout for the frame
this.getContentPane().setLayout(new FlowLayout(FlowLayout.LEADING));
Object[]mainData = {"Vehicles", "Bikes/Bicycles", "Boats", "Houses", "Businesses", "Objects", "Jobs", "Ranks", "Licenses", "VIP"};
JPanel controls = new JPanel(new BorderLayout(5,5));
list1 = new JList<Object>(mainData);
list1.setVisibleRowCount(10);
next = new JButton("Next");
next.addActionListener(this);
controls.add(new JScrollPane(list1));
controls.add(next, BorderLayout.PAGE_END);
controls.setBorder(new EmptyBorder(25,25,0,0));
add(controls);
}
#Override
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("Next")) {
int index = list1.getSelectedIndex();
System.out.println("Index Selected: " + index);
String s = (String) list1.getSelectedValue();
System.out.println("Value Selected: " + s);
}
}
public void createAndShowGUI() {
//Create and set up the window.
JFrame f = new MTGSAMPServerReference();
//Display the window.
f.pack();
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(1200, 800);
f.setLocationRelativeTo(null);
list1.setSize(250, 250);
list1.setLocation(0, 0);
next.setSize(75, 25);
next.setLocation(251, 276);
MTGSAMPServerReference.this.repaint();
}
protected void paintComponent(Graphics g) {
//super.paintComponent(g); << Can't seem to get this to work.
Graphics2D g2 = (Graphics2D)g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.drawRect(0, 0, 50, 50);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
MTGSAMPServerReference gui = new MTGSAMPServerReference();
gui.createAndShowGUI();
}
});
}
}
I have worked with paintComponent() before, but still can't seem to figure out what I am doing wrong. I know that it has got to be a simple fix, but can't spot it for the life of me. Any ideas?
Any and all help is appreciated.
Thanks in advance!
Use the #Override annotation on your paintComponent method for a rude surprise. This is why using this annotation is very helpful, since it will flag you at compile time if you are not overriding a method when you think that you should be.
Solution: never "paint" in a JFrame for many reasons. Instead do what the tutorials tell you to do -- paint in a JPanel or JComponent's paintComponent(...) method. If you search this site you will find that we have told many folks here the same thing, and in fact I suggest that you do just that. I wouldn't be surprised if this question is closed as a duplicate since this is a fairly common question.
Note this won't "work" (and actually won't compile):
super.paintComponent(g); << Can't seem to get this to work.
for the same reason -- there is no super.paintComponent(g) for a JFrame.
Also, regarding,
I have worked with paintComponent() before, but still can't seem to figure out what I am doing wrong.
But if you look at your prior code, you'll see that this method was never used directly in a JFrame, and nor should it.
paintComponent() is a member of the JPanel class, not the JFrame class in which you are trying to call it.
That is why you are unable to call super.paintComponent(Graphics g). The compiler thinks you are creating your own completely unrelated method that also happens to be called paintComponent().
Create a class that inherits JPanel and copy and paster your paintComponent() method there.
Like Hovercraft Full Of Eels commented, you can check that you are correctly overriding methods by adding the #Override tag directly over the method header; if you receive an error, you are doing something wrong.
For more information about JPanel and JFrame, see my answer to this question.
I am new to swing, can anyone help me out with this...
It is not showing my "label" , instead it shows me only components which are in the "panel" class.
One more question, can anyone clarify me about LayoutManagers ?
Can 2 or more LayoutManagers be used in a frame ? like for the frame i will be using FlowLayout and i have a JPanel added to the frame for which i will be using BoxLayout ... is it possible in the first place ??
import javax.swing.*;
import java.awt.event.*;
import java.awt.Graphics;
public class JForm1 extends JFrame
{
public JForm1()
{
init();
}
public static void main(String[] args)
{
JForm1 form = new JForm1();
}
public void init()
{
JFrame frame = new JFrame("My Form 1");
frame.setSize(500,500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
getContentPane().setLayout(new BoxLayout(this,BoxLayout.PAGE_AXIS));
JLabel label = new JLabel("Enter your Name : ");
panel MyPanel = new panel();
frame.getContentPane().add(label);
frame.getContentPane().add(MyPanel);
frame.setVisible(true);
}
}
class panel extends JPanel implements ActionListener
{
JButton submitButton;
JTextField text;
panel()
{
this.setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));
}
public void paintComponent(Graphics g)
{
text = new JTextField("Enter Name here");
text.setSize(100,25);
submitButton = new JButton("Submit");
submitButton.setSize(50,90);
submitButton.setBounds(200, 0, 80, 80);
submitButton.addActionListener(this);
this.add(text);
this.add(submitButton);
}
public void actionPerformed(ActionEvent event)
{
if(event.getSource()==submitButton)
{
System.out.println("The Entered Name is : "+text.getText());
}
}
}
What is this ?:
public void paintComponent(Graphics g)
{
text = new JTextField("Enter Name here");
text.setSize(100,25);
submitButton = new JButton("Submit");
submitButton.setSize(50,90);
submitButton.setBounds(200, 0, 80, 80);
submitButton.addActionListener(this);
this.add(text);
this.add(submitButton);
}
This code has nothing to do in paintComponent. paintComponent is about "painting a component", ie, paint a rectangle, draw a line, fill an oval, etc... This is absolutely not the place where to add your components. Instead, call that code in your constructor.
Additionally, if you are using LayoutManager's (which you should), calling setSize/setBounds/setLocation is useless (dimply remove those calls).
A few more things:
If you override paintComponent, make sure to invoke the super-method
Don't extends JFrame if not needed (here it is clearly not needed)
Follow Java naming conventions (class names should start with an UpperCase letter, variables and methods with a lowerCase letter)
All Swing-related code must be called on the EDT. Start your UI within a SwingUtilities.invokeLater() block.
Try by changing layout to FlowLayout for mypanel.
mypanel.setLayout(new FlowLayout());