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why repeated call to repaint() method did not work

My objective is to put a button and a circle on the JFrame. When i click the button the circle should move randomly on the panel/frame.
But when i click the button the circle just move once only and after putting SOP statements i found that "frame.repaint()" is getting called multiple times but this call is triggering the "paintComponent" method only once, the very first time (defined in class Panel1). Its very strange!
I have also provided another code which works as expected but has no buttons to trigger the animation. I have read that repaint() requests are coalesced together and executed once, then how come the second program works?
import java.awt.event.*;
import java.awt.Graphics.*;
import javax.swing.*;
import java.awt.*;
public class SimpleGui3c_4 {
public static void main(String args[]) {
Frame1 frame = new Frame1();
frame.go();
}
}
class Frame1 {
JFrame frame;
Panel1 p;
void go() {
frame = new JFrame();
JButton button1 = new JButton("Color Change");
p = new Panel1();
frame.setSize(500,500);
frame.setVisible(true);
frame.getContentPane().add(BorderLayout.SOUTH, button1);
frame.getContentPane().add(BorderLayout.CENTER, p);
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
button1.addActionListener(new ColorActionListener());
}
class ColorActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
for(int i=0;i<130;i++) {
System.out.println("Frame repaint started");
frame.repaint();
try {
Thread.sleep(5000);
}catch(Exception ex) {}
System.out.println("Frame repaint ended");
}
}
}
class Panel1 extends JPanel {
public void paintComponent(Graphics g) {
System.out.println("Inside the paint Component method");
int x = (int)(Math.random()*100);
int y = (int)(Math.random()*100);
g.setColor(Color.BLUE);
g.fillOval(x,y,100,100);
System.out.println("Exiting the paint component method");
}
}
}
Code which works but has no button to trigger the animation, it works as soon as i run the code. I am not sure why the below program works and the above program fails!
import javax.swing.*;
import java.awt.*;
public class SimpleAnimation {
int x = 70;
int y = 70;
public static void main(String args[]) {
SimpleAnimation gui = new SimpleAnimation();
gui.go();
}
public void go() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyDrawPanel drawPanel = new MyDrawPanel();
frame.getContentPane().add(drawPanel);
frame.setSize(300,300);
frame.setVisible(true);
for(int i = 0;i<130;i++) {
//x++;
//y++;
drawPanel.repaint();
try {
Thread.sleep(50);
}catch(Exception ex) {}
}
}//close go
class MyDrawPanel extends JPanel {
public void paintComponent(Graphics g) {
g.setColor(Color.WHITE);
g.fillRect(0,0,this.getWidth(), this.getHeight());
int x = (int)(Math.random()*70);
int y = (int)(Math.random()*70);
g.setColor(Color.green);
g.fillOval(x,y,40,40);
}
}
}

I have also provided another code which works as expected but has no buttons to trigger the animation.
The difference between the two pieces of code is context within which they are been called.
The code that "works" is actually been updated out side the context of the Even Dispatching Thread, in the "main" thread, which means that doing something like Thread.sleep won't prevent the UI from been updated.
The code which does not work is been updated from with the content of the Event Dispatching Thread (from within the ActionListener), which is prevent the EDT from processing new paint requests until after the actionPerformed method returns
Another issue you will face relates to when you decide to update the position of the circle.
paintComponent can be called for all a number of different reasons, many which you don't control. Painting should focus on painting the current state and should never modify it (directly or indirectly). Instead, you should use some kind of update method, whose job it is, is to update the x/y position of the circle and trigger a new paint cycle.
I would highly recommend that you stop and take the time to read through:
Concurrency in Swing for a more detail explanation
How to use Swing Timers for a possible solution
Performing Custom Painting and Painting in AWT and Swing for a better understanding into how painting actually works in Swing.
Your problem is rookie mistake which comes about from not understanding how the API actually works and not understanding the tools available to solve it
There are a number of other "issues" which would result in undesirable behaviour, like not calling setVisible last, so the UI doesn't need be updated again to ensure that the components been added are visible.
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 javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class SimpleGui3c_4 {
public static void main(String args[]) {
new SimpleGui3c_4();
}
public SimpleGui3c_4() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
Frame1 frame = new Frame1();
frame.go();
}
});
}
public interface Animatable {
public void update();
}
public class Frame1 {
JFrame frame;
Panel1 p;
void go() {
frame = new JFrame();
JButton button1 = new JButton("Color Change");
p = new Panel1();
frame.getContentPane().add(BorderLayout.SOUTH, button1);
frame.getContentPane().add(BorderLayout.CENTER, p);
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
button1.addActionListener(new ColorActionListener(p));
frame.pack();
frame.setVisible(true);
}
class ColorActionListener implements ActionListener {
private Animatable parent;
public ColorActionListener(Animatable parent) {
this.parent = parent;
}
public void actionPerformed(ActionEvent e) {
JButton btn = (JButton) e.getSource();
btn.setEnabled(false);
Timer timer = new Timer(5000, new ActionListener() {
private int counter = 0;
#Override
public void actionPerformed(ActionEvent e) {
System.out.println("Frame repaint started");
parent.update();
counter++;
if (counter >= 130) {
((Timer)e.getSource()).stop();
btn.setEnabled(true);
}
}
});
timer.setInitialDelay(0);
timer.start();
}
}
class Panel1 extends JPanel implements Animatable {
private int xPos, yPos;
public Panel1() {
update();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
System.out.println("Inside the paint component method");
g.setColor(Color.BLUE);
g.fillOval(xPos, yPos, 100, 100);
System.out.println("Exiting the paint component method");
}
#Override
public void update() {
System.out.println("Inside the update method");
xPos = (int) (Math.random() * 100);
yPos = (int) (Math.random() * 100);
repaint();
}
}
}
}

Trying to use key listener but shape won't move

I have added a keylistener to try and get a shape to move right when I press the right arrow key. But it isn't working. I don't really know how to use keylistner that well. Can someone help me.
This is the code:
package walkingman;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Color;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class WalkingMan extends JPanel implements KeyListener{
int x = 0;
int y = 0;
#Override
public void paint(Graphics g){
super.paint(g);
g.fillOval(x, y, 150, 150);
}
public static void main(String[] args) throws InterruptedException {
JFrame frame = new JFrame ("Walking Man");
frame.setSize(1080,720);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
WalkingMan game = new WalkingMan();
frame.add(game);
while (true){
game.repaint();
game.keyPressed(e);
}
}
#Override
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_RIGHT){
x++;
}
repaint();
}
#Override
public void keyReleased(KeyEvent e) {
}
#Override
public void keyTyped(KeyEvent e) {
}
}

There are a few issues with your code
You never add the KeyListener to the panel.
A KeyListener for a JPanel would only work if it is focusable & also focused.
Override paintComponent instead of paint.
Call setVisible at the end of the method.
Get rid of the whole while-loop, it'll only cause problems.
Use KeyBindings instead of KeyListeners.
Fixed code without key bindings:
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Color;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class WalkingMan extends JPanel implements KeyListener {
int x = 0;
int y = 0;
#Override
public void paintComponent(Graphics g) { // Overide paintComponent, not paint
super.paintComponent(g);
g.fillOval(x, y, 150, 150);
}
public WalkingMan() { // Class Constructor
setFocusable(true); // KeyListeners only work if the component is focusable
addKeyListener(this); // Add the KeyListener implemented by this class to the instance
}
public void createAndShowGUI() {
JFrame frame = new JFrame("Walking Man");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
WalkingMan game = new WalkingMan();
frame.add(game);
frame.setSize(1080, 720);
frame.setVisible(true); // Call setVisible after adding the components
game.requestFocusInWindow(); // Request focus for the panel
}
public static void main(String[] args) throws InterruptedException {
new WalkingMan().createAndShowGUI();
}
#Override
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
x++;
}
repaint();
}
#Override
public void keyReleased(KeyEvent e) {
}
#Override
public void keyTyped(KeyEvent e) {
}
}

Set frame well before it is displayed And remove the while loop which is still running.
public static void main(String[] args) throws InterruptedException {
JFrame frame = new JFrame ("Walking Man");
frame.setSize(1080,720);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
WalkingMan game = new WalkingMan();
frame.add(game);
frame.setVisible(true);//Call visible method here
}

Why not restructure your code in a much clear way like this
import javax.swing.*;
import java.awt.*;
import javax.swing.border.LineBorder;
import java.awt.Color;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
public class WalkingMan extends JFrame{
EmilsKeyClass keyBoard = new EmilsKeyClass();
public WalkingMan (){
add(keyBoard,BorderLayout.CENTER);
keyBoard.addKeyListener(new KeyAdapter(){
#Override
public void keyPressed(KeyEvent e){
if(e.getKeyCode()== KeyEvent.VK_ENTER){
x++;
repaint();
}
}
});
keyBoard.setFocusable(true);
}
public static void main(String [] args){
WalkingMan frame = new WalkingMan ();
frame.setTitle("Walking Man");
frame.setSize(1080,720);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public class EmilsKeyClass extends JPanel{
int x = 0;
int y = 0;
public EmilsKeyClass(){
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
super.paint(g);
g.fillOval(x, y, 150, 150);
//your code
}
}
}

Painting inside Swing Timer not working

I never worked with Timers before so my problem is probably stupid one really. My program draws a circle which is red and after random seconds the circle should change its color to green. I just made a swing timer as you can see below in the code. And it enters actionPerformed() method but it doesn't change color. Could you help me somehow fix my problem with changing colors?
My code:
package igrica;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class ChangingCircle implements ActionListener{
JFrame frame;
Timer timer;
Random r;
public static void main(String[] args) {
ChangingCircle gui = new ChangingCircle();
gui.go();
}
public void go() {
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyPanel panel = new MyPanel();
frame.getContentPane().add(BorderLayout.CENTER, panel);
frame.setSize(300, 300);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent event) {
frame.repaint();
}
class MyPanel extends JPanel {
public void paintComponent(Graphics g) {
g.setColor(Color.red);
g.fillOval(100, 100, 100, 100);
Random r = new Random();
Timer timer = new Timer(r.nextInt(5000) + 1000, new ActionListener() {
public void actionPerformed(ActionEvent ev) {
System.out.println("Timer out");
g.setColor(Color.green);
g.fillOval(100, 100, 100, 100);
}
});
timer.start();
}
}
}

There's quite the mess in your code. Try this:
public class ChangingCircle {
Color color = Color.RED;
MyPanel panel = new MyPanel();
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
ChangingCircle gui = new ChangingCircle();
gui.go();
});
}
public void go() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(panel, BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
Random r = new Random();
Timer timer = new Timer(r.nextInt(5000) + 1000, new ActionListener() {
public void actionPerformed(ActionEvent ev) {
System.out.println("Timer");
color = Color.GREEN;
panel.repaint();
}
});
timer.setRepeats(false);
timer.start();
}
class MyPanel extends JPanel {
private int size = 100, loc = 100;
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(color);
g.fillOval(loc, loc, size, size);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(size + loc, size + loc);
}
}
}
The idea is that the timer only changes the property of the shape to be drawn and then calls repaint() to reflect the change. The paintComponent is called whenever it is needed, even in quick succession and should return quickly.
Specific Notes:
Start Swing from the EDT.
Create and start the timer from outside of paintComponent since it is called many times and that will create and start many timers.
You should probably set the timer not to repeat.
Call super.paintComponent(g); as the first thing inside paintComponent.
You seem to have an ActionListener that does nothing.
General tips:
Use the #Override annotation when applicable.
Call pack() on the frame instead of setting its size manually and #Override the getPreferredSize method of the component you paint on. Return a meaningful size based on what you draw.
Use add(component, location) and not the other way around (deprecated).
Don't use fields when local variables will do (Random r for example).
Use uppercase constant names (Color.RED instead of Color.red).

Don't initiate a Timer from within a paintComponent method. This method should be for painting and painting only. Instead start the Timer in your constructor and within your Timer's actionPerromed and call repaint(), change the state of a field of the class, and use that information within the paintComponent use that field to draw any new information.
e.g.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class ChangingCircle {
JFrame frame;
public static void main(String[] args) {
ChangingCircle gui = new ChangingCircle();
gui.go();
}
public void go() {
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyPanel panel = new MyPanel();
frame.getContentPane().add(BorderLayout.CENTER, panel);
frame.setSize(300, 300);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent event) {
frame.repaint();
}
class MyPanel extends JPanel {
private Random r = new Random();
private boolean draw = false;
public MyPanel() {
Timer timer = new Timer(r.nextInt(5000) + 1000, new ActionListener() {
public void actionPerformed(ActionEvent ev) {
draw = true;
repaint();
}
});
timer.setRepeats(false);
timer.start();
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
if (draw) {
g.setColor(Color.red);
g.fillOval(100, 100, 100, 100);
}
}
}
}
Also, don't forget to call the super's paintComponent method from within your override.
If you need to change colors, give the JPanel a Color field, say called color and change it's value from within the Timer, and then call repaint(). Again within paintComponent, use the value of that field to draw the oval with. Also in this situation, the Timer should repeat, so get rid of timer.setRepeats(false) in that situation.

The timer works asynchronously and paintComponent finishes before finishing the work of timer.

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();
}
});
}
}

How to update java canvas dynamically?

Problem: I am trying to update the canvas with new painting objects based on user action. The canvas dosent get updated.
What i have done: The user interacts with the DnD action,The transferrable object reaches the canvas, Calls an update graphics method created by me. And the method simply uses the aldready created graphics 2d object and draws images using it.I have checkd the DnD action,the object is properly recived at canvas class and i was able to print them out using System.out.println.
A sample code,that has a similar function to that of mine,
Paint class:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JPanel;
public class PaintPanel extends JPanel{
private Graphics2D drawImage;
public PaintPanel()
{
}
#Override
public void paint(Graphics g) {
drawImage = (Graphics2D) g;
drawImage.setColor(Color.WHITE);
drawImage.fillRect(0, 0, getWidth(), getHeight());
}
public void updateGraphics(int length,int width)
{
drawImage.setColor(Color.black);
drawImage.drawRect(100, 150, length, width);
repaint();
}
}
mainframe class:
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
public class MainPaint extends JFrame{
public MainPaint()
{
setTitle("test paint");
setSize(400,400);
setLayout(new BorderLayout());
final PaintPanel paintPan = new PaintPanel();
JButton testButon = new JButton("Display shape");
add(paintPan,BorderLayout.CENTER);
add(testButon,BorderLayout.PAGE_END);
testButon.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
paintPan.updateGraphics(50,50);
repaint();
}
});
setVisible(true);
}
public static void main(String[] args)
{
new MainPaint();
}
}

Graphics2D drawImage; //source of the problem!
Don't attempt to cache a Graphics (or Graphics2D) instance! Instead:
Add the new objects to a list
Call repaint().
In paintComponent(Graphics) draw the list of objects.
An alternative to that is to use a BufferedImage as the drawing object. See this answer for an example.
Update - SSCCE based on latest code.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MainPaint extends JFrame {
public MainPaint() {
setTitle("test paint");
setSize(400, 400);
setLayout(new BorderLayout());
final PaintPanel paintPan = new PaintPanel();
JButton testButon = new JButton("Display shape");
add(paintPan, BorderLayout.CENTER);
add(testButon, BorderLayout.PAGE_END);
testButon.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
paintPan.updateGraphics(50, 50);
repaint();
}
});
setVisible(true);
}
public static void main(String[] args) {
new MainPaint();
}
}
class PaintPanel extends JPanel {
private int x, y;
private Color color = null;
public PaintPanel() {
setBackground(Color.ORANGE);
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D drawImage = (Graphics2D) g;
if (color != null) {
drawImage.setColor(color);
drawImage.drawRect(100, 150, x, y);
}
}
public void updateGraphics(int length, int width) {
color = Color.RED;
x = length;
y = width;
repaint();
}
}
Note
There are still a number of things about that code that need changing. I decided to stop at the earliest variant that worked to display the rectangle on button click.

I think you need to call the validate() method.