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A loop in action performed method Doesn't Working in java [closed]

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Question: Write JFrame that when you press the "start" button draws, and keep drawing random colored and sized filled ovals until the "stop" button is pressed.
Problem: loop inside the actionPerformed method() Doesn't Work.
The Code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class p6 extends JFrame implements ActionListener
{
String str;
JButton start,stop;
int h=0,w=0;
p6()
{
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(1500,1000);
start= new JButton("Start");
stop= new JButton("Stop");
setLayout(null);
start.setBounds(500, 50, 100,30);
stop.setBounds(610, 50, 100,30);
add(start);
add(stop);
start.addActionListener(this);
stop.addActionListener(this);
}
public void actionPerformed(ActionEvent ae)
{
String c=ae.getActionCommand();
if(c=="Start")
{
while(c!="Stop")
{
h+=20;
w+=20;
}
repaint();
}
str=" "+h+" "+w;
}
public void paint(Graphics g)
{
super.paintComponents(g);
g.drawString(str, 100, 100);
//g.drawOval(100, 100, 100, 100);
g.drawOval((int)Math.random()*2000,(int) Math.random()*2000, w,h);
}
public static void main(String[] args)
{
new p6();
}
}

Let's start with How do I compare strings in Java?. This is pretty basic Java 101 and something you REALLY need to understand.
The move onto Concurrency in Swing. Swing is a single threaded. This means that any long running or blocking operations executed within the context of the Event Dispatching Thread will cause the app to "hang" and prevent any further possible updates or interaction.
Swing is also not thread safe, which means that you should only ever update the UI or state the UI depends on, from within the context of the Event Dispatching Thread.
This might seem like a dilemma, but Swing also provides a useful tool to help work with these constraints, see How to user Swing Timer for more details.
Swing also has a well defined and documented painting process, see Painting in AWT and Swing and Performing Custom Painting to get a better understand of how painting works in Swing and how you're suppose to work with it
It is generally recommended not to override the paint method of top level containers (like JFrame). These tend to be composite components and trying to paint on them tends to end up not working very well.
Image from How to Use Root Panes
And you really should make the time to learn how to use layout managers, see Laying Out Components Within a Container. They will save many hours of frustration. The following examples makes use of both a BorderLayout and CardLayout.
import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
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 Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private CardLayout cardLayout;
private JPanel showPane;
private DrawingPane drawingPane;
public TestPane() {
setLayout(new BorderLayout());
cardLayout = new CardLayout();
showPane = new JPanel(cardLayout);
showPane.add(new EmptyPane(), "Empty");
drawingPane = new DrawingPane();
showPane.add(drawingPane, "Drawing");
cardLayout.show(showPane, "Empty");
add(showPane);
JButton startButton = new JButton("Start");
JButton stopButton = new JButton("Stop");
stopButton.setEnabled(false);
JPanel actionsPane = new JPanel();
actionsPane.add(startButton);
actionsPane.add(stopButton);
add(actionsPane, BorderLayout.SOUTH);
startButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
startButton.setEnabled(false);
stopButton.setEnabled(true);
drawingPane.start();
cardLayout.show(showPane, "Drawing");
}
});
stopButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
startButton.setEnabled(true);
stopButton.setEnabled(false);
drawingPane.stop();
cardLayout.show(showPane, "Empty");
}
});
}
}
public class EmptyPane extends JPanel {
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
}
public class DrawingPane extends JPanel {
private int h = 0, w = 0;
private Timer timer;
private Random rnd = new Random();
public DrawingPane() {
}
public void start() {
if (timer == null) {
timer = new Timer(500, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
h += 20;
w += 20;
repaint();
}
});
}
timer.start();
}
public void stop() {
if (timer != null) {
timer.stop();
}
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setColor(Color.RED);
int x = 0;
int y = 0;
if (w < getWidth() && h < getHeight()) {
x = rnd.nextInt(0, getWidth() - w);
y = rnd.nextInt(0, getHeight() - w);
}
g2d.drawOval(x, y, w, h);
g2d.dispose();
}
}
}
Why make use of CardLayout?
Based on the original code, when not painting, nothing is shown. So I made use of a CardLayout to switch to an "empty" state. Now, it wouldn't be very hard to derive a model to hold the state information and share that between the "empty" and "running" states and show something different on the "empty" state. Equally, we could make use of the glassPane, but I think we're drifting of course.
The purpose is to demonstrate ONE possible solution for showing different states.
Why use two different panes?
First, we don't "need" EmptyPane, we could get away with just an instance of JPanel, but, if you wanted to display something else when not drawing, this is one approach you could take.
The original code had a if statement which means that when not drawing, nothing is painted, so why waste the time and instead just show a "empty" pane instead.
Again, this is just a demonstration of one possible solution.

You have to add these lines before actionPerformed method,
start.setActionCommand("start");
stop.setActionCommand("stop");

Deleting a line in java when using paint(Graphics p)?

I have drawn a line using the below function:
public void paint(Graphics p) {
super.paint(p);
p.drawLine(600, 200, 580, 250);
}
I am wondering is there a way that I can delete this line?
Then is it possible to call this function in the main() method of a program?

You can use a flag to know whether the line is displaying or not.
As I said before you need to build your GUI towards JPanels and not JFrames. Also overriding paintComponent and not paint method.
For example, the following program displays a line or hides it when you click the JButton, adapt that logic to your own program with your own conditions.
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Line2D;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class LineDrawer {
private JFrame frame;
private JButton button;
public static void main(String[] args) {
SwingUtilities.invokeLater(new LineDrawer()::createAndShowGui); //Put our program on the EDT
}
private void createAndShowGui() {
frame = new JFrame(getClass().getSimpleName());
MyPane pane = new MyPane(); //Create an instance of our custom JPanel class
button = new JButton("Hide/Show");
button.addActionListener(e -> {
pane.setShowLine(!pane.isShowLine()); //Change the state of the flag to its inverse: true -> false / false -> true
});
frame.add(pane);
frame.add(button, BorderLayout.SOUTH);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
//Our custom class that handles painting.
#SuppressWarnings("serial")
class MyPane extends JPanel {
private boolean showLine;
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
if (showLine) { //If true, show line
g2d.draw(new Line2D.Double(50, 50, 100, 50));
}
}
#Override
public Dimension getPreferredSize() {
return new Dimension(300, 300); //For the size of our JPanel
}
public boolean isShowLine() {
return showLine;
}
public void setShowLine(boolean showLine) {
this.showLine = showLine;
this.repaint(); //Everytime we set a new state to showLine, repaint to make the changes visible
}
}
}
I can't post a GIF right now, but the program itself works. Btw the above code is called a Minimal, Complete and Verifiable Example and on your next questions you're encouraged to post one in order to get specific, faster and better answers to your questions.

Confusion with regarding to absolute positioning [duplicate]

In the below example, how can I get the JPanel to take up all of the JFrame? I set the preferred size to 800x420 but it only actually fills 792x391.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.image.BufferStrategy;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class BSTest extends JFrame {
BufferStrategy bs;
DrawPanel panel = new DrawPanel();
public BSTest() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLayout(new BorderLayout()); // edited line
setVisible(true);
setSize(800,420);
setLocationRelativeTo(null);
setIgnoreRepaint(true);
createBufferStrategy(2);
bs = getBufferStrategy();
panel.setIgnoreRepaint(true);
panel.setPreferredSize(new Dimension(800,420));
add(panel, BorderLayout.CENTER); // edited line
panel.drawStuff();
}
public class DrawPanel extends JPanel {
public void drawStuff() {
while(true) {
try {
Graphics2D g = (Graphics2D)bs.getDrawGraphics();
g.setColor(Color.BLACK);
System.out.println("W:"+getSize().width+", H:"+getSize().height);
g.fillRect(0,0,getSize().width,getSize().height);
bs.show();
g.dispose();
Thread.sleep(20);
} catch (Exception e) { System.exit(0); }
}
}
}
public static void main(String[] args) {
BSTest bst = new BSTest();
}
}

If you are having only one panel in frame and nothing else then try this:
Set BorderLayout in frame.
Add panel in frame with BorderLayout.CENTER
May be this is happening because of while loop in JPanel.(Not sure why? finding actual reason. Will update when find it.) If you replace it with paintComponent(g) method all works fine:
public BSTest() {
//--- your code as it is
add(panel, BorderLayout.CENTER);
//-- removed panel.drawStuff();
}
public class DrawPanel extends JPanel {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.BLACK);
System.out.println("W:" + getSize().width + ", H:" + getSize().height);
g2d.fillRect(0, 0, getSize().width, getSize().height);
}
}
//your code as it is.

Here's an alternative using pack instead.
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class PackExample extends JFrame {
public PackExample(){
JPanel panel = new JPanel();
panel.setPreferredSize(new Dimension(800,600));
panel.setBackground(Color.green);
add(panel);
pack();
setVisible(true);
}
public static void main(String[] args){
new PackExample();
}
}

This took me forever to figure out but its actually the simplest code ever.
Just create a parent panel and pass GridLayout then add your child panel like this.
JPanel parentPanel= new JPanel(new GridLyout());
JPanel childPanel= new JPanel();
parentPanel.add(childPanel);

If you want to fill the JFrame with the whole of JPanel you need to setUndecorated to true i.e. frame.setUndecorated(true);. But now you have to worry about your MAXIMIZE< MINIMIZE, and CLOSE Buttons, towards the top right side(Windows Operating System)

Trying to draw lines in java over an image i already drew but i can't get it on top of the image?

I have to draw an archery target with two black lines in the innermost circle that forms a cross, but every time i adjust the lines so that the lines are closer to the centre it goes behind the image instead of appearing on top. How can I stop this? Does it need to have a separate set of instructions entirely?
This is my code:
package sumshapes;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.*;
import javax.swing.*;
public class SumShapes extends JFrame
implements ActionListener {
private JPanel panel;
public void paint(Graphics g)
{
g.setColor(Color.BLACK);
g.drawLine(250, 200, 250, 200);
g.drawOval(140,90,200,200);
g.setColor(Color.BLACK);
g.fillOval(140,90,200,200);
g.drawOval(162,109,155,155);
g.setColor(Color.BLUE);
g.fillOval(162,109,155,155);
g.drawOval(183,129,112,112);
g.setColor(Color.RED);
g.fillOval(183, 129, 112, 112);
g.drawOval(210,153,60,60);
g.setColor(Color.YELLOW);
g.fillOval(210, 153, 60, 60);
g.setColor(Color.BLACK);
}
public static void main(String[] args) {
SumShapes frame = new SumShapes();
frame.setSize(500,400);
frame.setBackground(Color.yellow);
frame.createGUI();
frame.setVisible(true);
}
private void createGUI(){
setDefaultCloseOperation(EXIT_ON_CLOSE);
Container window = getContentPane();
window.setLayout (new FlowLayout());
}
public void actionPerformed(ActionEvent event) {
Graphics paper = panel.getGraphics();
paper.drawLine(20,80,120,80);
}
}

All your drawing should go into the paintComponent method of a lightweight component, such as a JPanel.
There should never be a need to call getGraphics. If you wish to change the drawing upon a particular action you should a) program the logic into paintComponent b) alter the logic in the Action c) call repaint on the Component
For example:
private JPanel panel = new JPanel(){
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);//call parent method first thing
//paint here
}
#Override
public Dimension getPreferredSize(){//provided so you can size this component as necessary
return new Dimension(500,400);
}
};
....
frame.add(panel);
frame.pack();
As an aside, I'd recommend placing all calls to to Swing components on the EDT - this means wrapping your Swing calls in the main method with SwingUtilities. eg
public static void main(String[] args) throws Exception {
SwingUtilities.invokeAndWait(new Runnable(){
#Override
public void run() {
SumShapes frame = new SumShapes();
....
}
});
}

JButton and JLabel dissappears when adding custom background

JButton and JLabel disappears when adding custom background. I don't see any problems in my program, but maybe you guys find an solution! I think it's only a little thing I forgot, but I can't figure it out.
Here's the code:
GameWindow.java:
setContentPane(new StartImagePanel(RollrackLogo));
out.println("adding JLWelcome");
JLWelcome.setText("Welcome to Rollrack, " + namewindow.name);
add(JLWelcome);
JLWelcome.setVisible(true);
out.println("JLWelcome added");
out.println("adding JBRandom");
JBRandom.setText("Random");
add(JBRandom);
JBRandom.setVisible(true);
out.println("added JBRandom");
The background appears perfect, but not the JButton and JLabel!
Code to the StartImagePanel.java:
public class StartImagePanel extends JComponent{
private Image image;
public StartImagePanel(Image image) {
this.image = image;
}
#Override
protected void paintComponent(Graphics g) {
g.drawImage(image, 0, 0, null);
}
}

Your button and label are added to your GameWindow frame while they should be added to its contentPane, setContentPane(new StartImagePanel(RollrackLogo)); instead. That's why they are not showing, they are added to the frame.
Make a variable of the StartImagePanel and add the button and label to it and they should show up.
StartImagePanel contentPanel = new StartImagePanel(RollrackLogo);
setContentPane(contentPanel);
...
out.println("adding JLWelcome");
JLWelcome.setText("Welcome to Rollrack, " + namewindow.name);
contentPanel.add(JLWelcome);
JLWelcome.setVisible(true);
out.println("JLWelcome added");
out.println("adding JBRandom");
JBRandom.setText("Random");
contentPanel.add(JBRandom);
JBRandom.setVisible(true);
out.println("added JBRandom");
Answer dispute
The claims in the first paragraph are plain wrong. Here is source that proves it.
import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class AddToCustomContentPane {
public static void main(String[] args) {
Runnable r = new Runnable() {
#Override
public void run() {
// the GUI as seen by the user (without frame)
JPanel gui = new JPanel(new FlowLayout());
gui.setBorder(new EmptyBorder(2, 3, 2, 3));
gui.setBackground(Color.RED);
JFrame f = new JFrame("Demo");
f.setContentPane(gui);
// Acid test. Can we add buttons direct to the frame?
f.add(new JButton("Button 1"));
f.add(new JButton("Button 2"));
// Ensures JVM closes after frame(s) closed and
// all non-daemon threads are finished
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
// See http://stackoverflow.com/a/7143398/418556 for demo.
f.setLocationByPlatform(true);
// ensures the frame is the minimum size it needs to be
// in order display the components within it
f.pack();
// should be done last, to avoid flickering, moving,
// resizing artifacts.
f.setVisible(true);
}
};
// Swing GUIs should be created and updated on the EDT
// http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html
SwingUtilities.invokeLater(r);
}
}
Edit after the custom panel code was given
Here's a snippet that works to show both button and label on a black image background, I removed that was not needed (listeners).
public static void main(String[] v) {
class StartImagePanel extends JPanel {
private Image image;
public StartImagePanel(Image image) {
this.image = image;
}
#Override
protected void paintComponent(Graphics g) {
g.drawImage(image, 0, 0, null);
}
}
class GameWindow extends JFrame{
public GameWindow() {
BufferedImage RollrackLogo;
RollrackLogo = new BufferedImage(400,200,BufferedImage.TYPE_INT_RGB);
final JButton JBRandom = new JButton();
final JLabel JLWelcome = new JLabel();
setDefaultCloseOperation(EXIT_ON_CLOSE);
StartImagePanel panel = new StartImagePanel(RollrackLogo);
setContentPane(panel);
setExtendedState(MAXIMIZED_BOTH);
setVisible(true);
JLWelcome.setText("Welcome to Rollrack");
panel.add(JLWelcome);
JLWelcome.setVisible(true);
JBRandom.setText("Random");
panel.add(JBRandom);
JBRandom.setVisible(true);
}
}
GameWindow window = new GameWindow();
window.pack();
window.setVisible(true);
}

I rather use an instance of a JFrame, instead of extending it, as #Andrew Thompson suggested in another question.
However, if you're extending it, it might be a good practice to call super() in the constructor.
Additionally, we may need to know what is going on in your StartImagePanel.
It seems, to me, to be the problem.
Ensure both your GameWindow and StartImagePanel extend properly their superclasses (call super();).
Ensure your StartImagePanel has a proper Layout.
Add your components before you set your frame visible. This also means you won't need JLWelcome.setVisible(true);.
Ensure that your code is executed in the EDT (Event-Dispatch Thread).
Example:
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.*;
#SuppressWarnings("serial")
public class GameWindow extends JFrame{
BufferedImage rollrackLogo;
JButton jbRandom;
JLabel jlWelcome;
public GameWindow() {
super();
jbRandom = new JButton("Random");
jlWelcome = new JLabel("Welcome to Rollrack, " +
namewindow.name);
rollrackLogo = new BufferedImage(400, 200,
BufferedImage.TYPE_INT_RGB);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setContentPane(new StartImagePanel(rollrackLogo));
// Add your components.
add(jlWelcome);
add(jbRandom);
addKeyListener(new KeyListener() {
#SuppressWarnings("static-access")
#Override
public void keyPressed(KeyEvent e) {
if(e.getKeyCode() == e.VK_ESCAPE){
System.exit(7);
}
}
#Override
public void keyReleased(KeyEvent arg0) {}
#Override
public void keyTyped(KeyEvent arg0) {}
});
// Pack, or otherwise set fullscreen.
pack();
// Now, set frame visible.
setVisible(true);
}
}
Edit: Now that you've posted the code for your StartImagePanel, I see that you're extending JComponent. Follow my previous advice, (call super), set a Layout, and extend JPanel instead.