We Keep Coding

Custom JComponent (A Line) Doesn't Show Up On JPanel

It shows the line without jpanel on jframe, but it doesn't when I add it to jpanel. I've tried setting the layout manager of jpanel to null but no result. I want to use JComponents for drawing lines because I want them clickable.
Main.java file:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
class Main {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
//Parent Panel
JPanel panel = new JPanel();
panel.setBackground(Color.YELLOW);
panel.setLayout(null);
//Add Line To Panel
Line line = new Line(new Point2D.Double(20,20), new Point2D.Double(180,180));
panel.add(line);
panel.repaint();
frame.add(panel);
frame.setVisible(true);
}
}
class Line extends JComponent {
private final Point2D start, end;
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.BLUE);
g2.setStroke(new BasicStroke(2.0F));
g2.draw(new Line2D.Double(start,end));
}
public Line( Point2D start, Point2D end){
this.start = start;
this.end = end;
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("mouse clicked");
}
});
}
}

It shows the line without jpanel on jframe, but it doesn't when I add it to jpanel
Swing components are responsible for determining their own preferred size.
When you add a component to a panel, the layout manager will then set the size/location of the component based on the rules of the layout manager.
When you add a component to the frame you really add it to the content pane of the frame which is a Jpanel which uses a BorderLayout by default. So the component is sized to fill the space available in the frame.
panel.setLayout(null);
You then added the component to a panel with a null layout. Now you are responsible for setting the size/location of the component. If you don't the size is (0, 0) so there is nothing to paint.
You should override the getPreferredSize() method of your class to return the preferred size of the component. Then layout managers can do their job.
If you really need a null layout, then the size of the component should be set in the application code, not it the Line class itself.
But now my line has a big container that listens for any clicks,
If you want hit detection then you override the contains(...) method.
Here is a basic example implementing the above suggestions:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.awt.Rectangle;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Line extends JComponent
{
private Line2D.Double line;
public Line( Point2D start, Point2D end)
{
line = new Line2D.Double(start, end);
addMouseListener(new MouseAdapter()
{
#Override
public void mouseClicked(MouseEvent e)
{
System.out.println("mouse clicked");
}
});
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor( Color.BLUE );
g2.setStroke( new BasicStroke(2.0F) );
g2.draw( line );
}
#Override
public Dimension getPreferredSize()
{
Rectangle bounds = line.getBounds();
int width = bounds.x + bounds.width;
int height = bounds.y + bounds.height;
return new Dimension(width, height);
}
#Override
public boolean contains(int x, int y)
{
double distance = line.ptSegDist( new Point2D.Double(x, y) );
return distance < 2;
}
public static void main(String[] args)
{
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
//Parent Panel
JPanel panel = new JPanel();
panel.setBackground(Color.YELLOW);
//Add Line To Panel
Line line = new Line(new Point2D.Double(20,20), new Point2D.Double(180,180));
panel.add(line);
panel.repaint();
frame.add(panel);
frame.setVisible(true);
}
}

Add custom size in Line constructor.
public Line( Point2D start, Point2D end){ ...
this.setSize(200, 200); }
Updated to fit also with painted Graph
Advice to change from JComponent to JPanel in order to see background
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
class Main {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
//Parent Panel
JPanel panel = new JPanel();
panel.setSize(300,300);
frame.add(panel);
panel.setBackground(Color.YELLOW);
panel.setLayout(null);
//Add Line To Panel
Line line = new Line(new Point2D.Double(20,20), new Point2D.Double(180,180));
panel.add(line);
frame.setVisible(true);
}
}
class Line extends JPanel {
private final Point2D start, end;
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setBackground(Color.RED);
g2.setColor(Color.BLUE);
g2.setStroke(new BasicStroke(2.0F));
g2.draw(new Line2D.Double(start,end));
Rectangle r = g2.getClipBounds();
System.out.println(r.x+":"+r.y);
}
public Line( Point2D start, Point2D end){
this.start = start;
this.end = end;
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("mouse clicked at "+e.getX()+":"+e.getY());
}
});
int max_x = (int) Math.max(start.getX(), end.getX());
int max_y = (int) Math.max(start.getY(), end.getY());
System.out.println("max x="+max_y+",y="+max_y);
setSize(max_x,max_y);
setVisible(true);
setBackground(Color.GREEN);
}
}
Note: Only inside_green clicks allowed !

Java questions about coordinates with Graphics

If I create a JFrame 800x600 pixels and draw a line from (0,0) to (800,600) it doesn't go from corner to corner, so, where is the (0,0) and where is the (800,600)?
Here is the code
import java.awt.Graphics;
import javax.swing.JFrame;
public class Point0_0test extends JFrame {
public Point0_0test() {
setTitle("Test");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(800, 600);
setLocationRelativeTo(null);
}
#Override
public void paint(Graphics g) {
super.paint(g);
g.drawLine(0, 0, 800, 600);
}
public static void main(String[] args) {
Point0_0test test = new Point0_0test();
test.setVisible(true);
}
}
Here you can see what appears when the program is running

If you want a drawing area that's 800 x 600 pixels, then set a drawing area that's 800 x 600 pixels. Who cares how big the frame is?
Here's a simple drawing GUI that I created. I made it 400 x 300 pixels so it would fit in the answer easier.
Here's the code. It's a minimal, runnable example for setting the size of the drawing area.
import java.awt.BasicStroke;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class SimpleDrawingArea implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new SimpleDrawingArea());
}
#Override
public void run() {
JFrame frame = new JFrame("Simple Drawing Panel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new DrawingPanel());
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public class DrawingPanel extends JPanel {
private static final long serialVersionUID = 1L;
public DrawingPanel() {
this.setPreferredSize(new Dimension(400, 300));
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setStroke(new BasicStroke(4f));
g2d.drawLine(0, 0, 400, 300);
}
}
}

The JFrame size and coordinates count the size of the decorations, such as the top part of the window contains the bar with the close button, the rest contain the extra outline that is added on Windows(Ubuntu, at least, doesn't seem to add an extra outline). In order to get a line like you would want to, you should use JFrame.getInsets(), which returns the size of the GUI that decorates the JFrame, like this:
import java.awt.Insets;
#Override
public void paint(Graphics g) {
super.paint(g);
Insets in = getInsets();
g.drawLine(in.left, in.top, 800-in.right, 600-in.bottom);
}
Edit: this means that you don't have an actual 800x600 space. The Insets class seems to be "created" when setVisible(true) is called, as far as I can tell. So this would be how the code for that looks like:
import javax.swing.JFrame;
import java.awt.Insets;
import java.awt.Graphics;
public class InsetsTest extends JFrame {
public InsetsTest() {
super();
setTitle("Test");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(800,600);
setVisible(true);
Insets insets= getInsets();
setSize(800+insets.right+insets.left,600+insets.top+insets.bottom);
setLocationRelativeTo(null);
}
#Override
public void paint(Graphics g) {
super.paint(g);
Insets in = getInsets();
g.drawLine(in.left, in.top, 800+in.left, 600+in.top);
}
public static void main(String[] args) {
InsetsTest test = new InsetsTest();
test.setVisible(true);
}
}```

The window size should be defined without OS specific window decoration.
Try to add
this.setUndecorated(true);
before the
this.setVisible(true);

Repaint() does not work after adding more components to JPanel in Swing, Java

I am starting with Java and want to make a simple pong game to get into the ways of displaying stuff in java. I have created 2 classes that both extend JPanel and call the repaint() function every 16.6 milliseconds. I added both to a JPanel which I added to the frame, but only the component I added first displays.
I've tried to revalidate() after repaint() in both classes and made sure that the Timer actually works and that it's actionPerformed() method is actually called.
This is the main method:
public class Main {
public static void main(String[] args){
JFrame frame = new JFrame("Pong");
//...
JPanel mainPanel = new JPanel();
mainPanel.add(new Player());
mainPanel.add(new Ball(frameWidth/2, frameHeight/2 -40));
frame.add(mainPanel);
}
}
This is the important code for the classes (It's basically the same for both of them):
public class Player extends JPanel {
public Player(){
setPreferredSize(new Dimension(Main.frameWidth, Main.frameHeight));
setBackground(Color.BLACK);
new Timer(1000/60, new ActionListener(){
public void actionPerformed(ActionEvent e){
update();
repaint();
}
}).start();
}
//...
public void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(x, y, width, height);
}
}
(Of coure I left things like #Override or unneseccary functions out to shorten the code)
This code only paints the Player, altough I want it to display all the components of mainPanel.
This is an example that you can (hopefully) run. I had to split it up into 3 files, since I suck at anonymus classes:
Main.java
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Main {
public static void main(String[] args){
JFrame frame = new JFrame("Pong");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(800, 800);
JPanel mainPanel = new JPanel();
mainPanel.add(new Player());
mainPanel.add(new Ball());
frame.add(mainPanel);
frame.setVisible(true);
}
}
///////
Player.java
//////
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Player extends JPanel{
private int x = 20, y = 300, width = 20, height = 100;
public Player(){
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000/60, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e){
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(x, y, width, height);
}
}
//////
Ball.java
//////
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Ball extends JPanel{
private int x = 20, y = 300, width = 20, height = 100;
public Ball(){
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000/60, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e){
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(x, y, width, height);
}
}

In method paintComponent() of class Player, you paint the exact same Rectangle each time. In order to achieve animation, each time you paint the rectangle you need to change either its size or location or both. What do you expect the Player to do? Should it move up and down along the left edge of the window? Have you seen the lesson entitled How to Use Swing Timers which is part of Oracle's Java Tutorial?
EDIT
I see now that Player hides Ball, because of the default layout manager of JPanel. The below code is essentially the code you posted but I set GridLayout as the layout manager for mainPanel. Also, a java source code file may contain more than one class but exactly one class must be public. Hence in the below code only class Main is public.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Main {
public static void main(String[] args) {
JFrame frame = new JFrame("Pong");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel mainPanel = new JPanel(new GridLayout(0, 2));
mainPanel.add(new Player());
mainPanel.add(new Ball());
frame.add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
}
class Player extends JPanel {
public Player() {
setBorder(BorderFactory.createLineBorder(Color.RED, 2, false));
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000 / 60, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(20, 100, 20, 100);
}
}
class Ball extends JPanel {
public Ball() {
setBorder(BorderFactory.createLineBorder(Color.CYAN, 2, false));
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000 / 60, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(300, 300, 10, 10);
}
}
And here is a screen capture of the GUI...

I just realized that if I extend my window manually, the second JPanel shows up under the one responsible for the Player! This means that I'll need to set the Panels position somehow, right?
#Abra

Why is graphics not showing on my JFrame / JPanel?

When I run this code. The result is a window with the name. Fully blank. I tried editing background color and adding graphics (rectangle) etc but the same result keeps occurring .
Question: This ends up as a white screen on a window. No graphics or background color. Even though I added it to panel and added panel. How do I fix this?
Main.java
package ball.tec.main;
import javax.swing.JFrame;
import ball.tec.frame.Frame;
public class Main {
public static void main(String[] args) {
String Version = "0.1.2";
Frame f = new Frame();
f.setVisible(true);
f.add();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setResizable(false);
f.setSize(1500, 1000);
f.setTitle("RedBall V: " + Version);
}
}
Frame.java
package ball.tec.frame;
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Frame extends JFrame{
private static final long serialVersionUID = 1L;
public boolean debug = false;
//Creating panel object
JPanel panel = new JPanel();
//Graphics displayed
public void paintComponent(Graphics g) {
//Firstly Nothing pops up
g.setColor(Color.RED);
g.drawRect(20, 40, 10, 10);
//And this doesn't work.
this.setBackground(Color.RED);
}
//Add everything to 'panel'
public void add() {
add(panel);
//Even if I put it here it doesn't work ;-;
this.setBackground(Color.RED);
this.pack();
}
}

You don't use paintComponent() in a JFrame. What you probably intended to do was create a third class, extending JPanel. Add your paintComponent() there.
public class MyPanel extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.RED);
g.drawRect(20, 40, 10, 10);
this.setBackground(Color.RED);
}
}
f.add(new MyPanel());

How to make a JPanel inside a JFrame fill the whole window?

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)