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Java JPanel Graphics - Understanding how to draw a simple shape

Disclaimer: I'm new to Java. I'm new to Swing. And I'm sure it shows.
I've viewed quite a number of examples/tutorials of how to draw on a jpanel "canvas". But they mostly have the same basic format and put all of their drawLine/drawRect/drawArc inside the paintComponent() method. It seems assumed that people want to draw static things to the jpanel one time. But what if I want to change the jpanel object over the course of the program's runtime, like a paint program, or a game?
I suppose I need to be able to access the jpanel object, and internal methods to paint. I'm betting what I'm doing isn't best practices, but here is what I have:
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class PaintPanel extends JPanel {
public static JFrame frame;
private Graphics g = getGraphics();
public static void main(String[] args) {
frame = new JFrame();
frame.getContentPane().setBackground(new Color(32, 32, 32));
frame.setResizable(false);
frame.setBounds(1, 1, 800, 600);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
frame.setVisible(true);
frame.setLocationRelativeTo(null); // center frame on screen
PaintPanel paintPanel = new PaintPanel();
paintPanel.setBounds(10, 10, 100, 100);
paintPanel.setBackground(Color.red);
frame.add(paintPanel);
}
// constructor
public PaintPanel() {
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
}
public void DrawRect(Integer x, Integer y, Integer w, Integer h, Color color) {
g.setColor(color);
g.fillRect(x, y, w, h);
this.repaint(); // doesn't seem to do anything
}
}
This code results in a red panel box, but my user method DrawRect() doesn't draw anything.
I've read in some places that it's necessary to override the paintComponent() method. If there's nothing in it, what's the purpose?
How can I get my DrawRect() method to work?

The piece of the puzzle you're missing is the model object. There should be an external object that describes what should be drawn. In a game for example, it would be something that describes the current state of the game.
Your custom component looks at this model and takes the necessary steps to paint it. This is implemented in paintComponent and in helper methods you see fit to add.
To make an animation, you make a loop that modifies the model over time, and asks the custom component to redraw itself with repaint().

Only One Thread Paints in my JFrame object, why not the other? [duplicate]

This question already has answers here:
Why does the first panel added to a frame disappear?
(2 answers)
Closed 5 years ago.
I've been trying all day long to make this happen with no success. What can be going wrong?
I want 2 threads printing simultaneously in my JFrame:
Thread-1: Prints Squares
Thread-2: Prints Circles
I'am ending up with only one thread printing on the JFrame. The other get executed but don't print in the JFrame.
Look, only squares are getting printed:
This is my main class:
public class Main {
public static void main(String[] args) {
FigurePlacer circle = new FigurePlacer("circle");
FigurePlacer square = new FigurePlacer("square");
JFrame window = new JFrame();
window.add(circle);
window.add(square);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setTitle("Task");
window.setSize(700, 700);
window.setLocationRelativeTo(null);
window.setVisible(true);
}
}
This is the Threading Class:
import java.awt.Graphics;
import javax.swing.JPanel;
import java.awt.Color;
import java.util.Random;
public class FigurePlacer extends JPanel implements Runnable{
String figure;
final int width = 700;
final int height = 700;
int x_pos = 0;
int y_pos = 0;
int x_width = 50;
int y_height = 50;
public FigurePlacer(String str){
figure = str;
randomCoord();
Thread th = new Thread (this);
th.start();
}
private void randomCoord(){ //this ramdomize x,y coord to place a new object
Random random = new Random();
x_pos = random.nextInt(width);
y_pos = random.nextInt(height);
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK); //sets the black color in background
g.fillRect(0, 0, 700, 700);
System.out.println(figure);
switch (figure){
case "square":
g.setColor(Color.GREEN);
g.fillRect(x_pos, y_pos, x_width, y_height);
break;
case "circle":
g.setColor(Color.BLUE);
g.fillOval(x_pos, y_pos, x_width, y_height);
break;
}
}
#Override
public void run(){ //paints the objects
while (true){
randomCoord();
paintImmediately(x_pos, y_pos, x_width, y_height);
try{
Thread.sleep (50);
}
catch (InterruptedException ex){}
}
}
}

JFrame window = new JFrame();
window.add(circle);
window.add(square);
The default layout manager for a JFrame is the BorderLayout. When you add a component to a panel using the BorderLayout and don't specify a constraint then the component goes to the CENTER. However only one component can ever be displayed in the CENTER, so only the last component added is painted.
You could use the OverlayLayout, which allows you to stack two panels on top of one another. Of course you will need to make the top panel non-opaque.
The easier solution is to not attempt to use two panels, just create on panel that can display circles or squares.
Also, your painting code is wrong. You should not be using paintImmediately(...) to do painting. The paintComponent() method should paint every object every time the method is invoked. Try resizing your frame and you will see that all your object disappear since the paintComponent() method will clear all the old paintings.
See Custom Painting Approaches for the two common approaches for this kind of painting.

repaint() is not working in swing

package games;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class viza extends JPanel implements ActionListener {
/**
*
*/
private static final long serialVersionUID = 1L;
int x=0, y=200;
Timer tm =new Timer(5,this);
public viza(){
tm.start();
}
public void paintComponent(Graphics g){
g.setColor(Color.red);
g.fillRect(x, y, 20, 20);
}
public void actionPerformed(ActionEvent e){
x=x+1;
y=y+1;
if(x>300)
x=0;
if(x<0)
x=0;
repaint(); //after x and y are changet then I use repaint();
} // the frame is created and the new object is added into the frame.
public static void main(String[] args){
viza a=new viza();
JFrame frame = new JFrame();
frame.setSize(500,500);
frame.add(a);
frame.setVisible(true);
}
}[1]
The code is used to draw a filled rectangle on the panel. However when I start the program the object moves but the panel is not repainted. If I try and resize the window while the program is runing it does load properly. As soon as i stop doing that the panel or frame (Not sure) is not repainted anymore. So i end up whith a line.

You should clear the underlying pane before you re-draw the rectangle in its new position.
To do that, let the super.paintComponent() do that for you, since that would be the correct approach to custom painting in any JComponent:
public void paintComponent(Graphics g){
super.paintComponent(g); // let it do the default paint
g.setColor(Color.red);
g.fillRect(x, y, 20, 20);
}
Also you may want to add a default close operation to your frame (in main method) to exit the program after closing the frame:
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
Another tip is to set a bigger timeout for your Timer, because 5 milliseconds is occurring very fast and your user may not see the movement. Try something bigger than 50 or 100.
Good Luck.

Java drawn objects not updating properly

I have been playing around with Java's 2d painting tools and have hit a snag. I am attempting to move the objects. Here is the code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Test extends JPanel{
private int[] location = new int[2];
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.red);
g.fillArc(location[0], location[1], 100, 100, 45, 90);
g.setColor(Color.black);
g.fillArc((location[0]+50-10),(location[1]+50-10), 20, 20, 0, 360);
new Timer(2000, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
setLocation((location[0]+50),50);
repaint();
System.out.println("repainting");
}
}).start();
}
public void setLocation(int x, int y){
this.location[0] = x;
this.location[1] = y;
}
public static void main(String[] args){
JFrame jf=new JFrame();
jf.setDefaultCloseOperation
(JFrame.EXIT_ON_CLOSE);
jf.setPreferredSize(new Dimension(300,500));
jf.setLocation(100,100);
jf.add(new Test());
jf.pack();
jf.setVisible(true);
}
}
This only paints one of the two objects to the screen... it seems to be the second one as when I change the parameters of setLocation on [1] the one object it does paint moves. Any thoughts? Thanks
Edit: Edited above code to reflect what was said below.

You are adding two components to the JFrame in a default way. This will add the components BorderLayout.CENTER and so the second component will cover and obscure the first. You will want to read up on layout managers to fix this. Also read up on Swing Timers for simple animations, since your code, even if written correctly would do no animation.
If you want to move the drawing, then
Use only one Test JPanel
Override JPanel's paintComponent(...) method, not paint(...) method.
call the super.paintComponent(g) method first thing in your paintComponent method override.
Give the Test JPanel public methods to allow outside classes to change the location without having them directly futz with the field. Make the location field (name should begin with a lower-case letter) private just to be safe.
Use a Swing Timer to periodically call this method and change location, then call repaint() on the JPanel.

Painting a custom JButton and a text line

I'm designing an optimization system for public transport in a big city. So I have a map with some points on it, but don't care about it)
All I need is: my own JButton, which looks like a color-filled circle and a small text tag near it. I got some problems while overriding the paintComponent() method.. the round button is painted correctly, but not the text.
BUT, when i'm resizing the window manually, the text appears for a second, then it gets repainted again and dissapears.
Hope you guys understood my needs, thanks for help ;)
import java.awt.*;
import javax.swing.*;
public class JRoundButton extends JButton {
String label;
Color color;
int x,y;
public JRoundButton(Color color,int x,int y,String str)
{
label=str;
this.x=x;
this.y=y;
this.color=color;
}
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
Dimension size = getPreferredSize();
setPreferredSize(size);
this.setBounds(0, 0, 10, 10);
setContentAreaFilled(false);
g.setFont(new Font("Arial",Font.BOLD,14));
g.drawChars(label.toCharArray(), 0, label.length(), 12,12);
g.fillOval(0,0,8,8);
}
public void paintBorder(Graphics g)
{
g.setColor(Color.white);
g.drawOval(0,0, 9, 9);
}
public static void main(String[] args)
{
JButton button = new JRoundButton(Color.GRAY,150,150,"Times Square");
JFrame frame = new JFrame();
frame.getContentPane().setBackground(Color.black);
frame.setSize(300, 300);
frame.setVisible(true);
frame.add(button);
}
}

Seems that the call to 'setBounds( 0, 0, 10, 10 )' sets a component footprint that is too small to accomodate the text string. Extending the bounds to 100px wide and bringing down the point size to 6 looks to work okay.

1) NEVER set properties of the button in the paintComponent() method.
Dimension size = getPreferredSize();
setPreferredSize(size);
this.setBounds(0, 0, 10, 10);
setContentAreaFilled(false);
Get rid of the above code.
2) Dont set the Font of the Graphics object in the paintComponent() method. Thats what the setFont(...) method is used for.
3) There is no need to do any custom painting. If you want a circle, then add an Icon to the JLabel.
4) Don't override the paintBorder() method. If you want a Border then create a custom border and add it to the button using the setBorder() method.
In short there is no need to extend the button. Get rid of your JRoundButton class. Your code should simply look something like:
JButton = new JButton("Times Square");
button.setFont( new Font("Arial",Font.BOLD,14) );
button.setIcon( new OvalIcon(Color.WHITE, iconSize) );
Of course you will need to create an OvalIcon class but that is easy to implement since there are only three methods and you already know what the painting code should be.

I'd just cheat and use a unicode circle in the JButton's text. E.g.:
import javax.swing.*;
JFrame frame = new JFrame();
frame.getContentPane().add(new JButton("<html><font size='+10' color='red'>●</font> I'm next to a red circle!</html>"));
frame.pack();
frame.show();