Develop Reference

how to do auto-resizing drawings in JPanel?

what's the easiest way to have a drawing in a JPanel that resizes whenever the user resizes the JFrame?
I know that I can auto resize the panel with a BorderLayout but the drawings are not resized in this case. I am new to java and GUI programming and there are probably numerous solutions.
please give me a hint into the right direction to make e.g. the rectangle in
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.*;
public class DrawRect extends JPanel {
#Override
protected void paintComponent(Graphics g) {
g.drawRect(20, 20, 100, 100);
}
public static void main(String[] args) {
JFrame frame = new JFrame();
DrawRect panel = new DrawRect();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setPreferredSize(new Dimension(200, 200));
frame.getContentPane().add(panel);
frame.pack();
frame.setVisible(true);
}
}
auto-resizing whenever the frame is resized.

Provide positions and sizes as a proportion of the width and height of the panel. Whenever the panel is resized, the rendering engine will schedule a call to the paintComponent() method and the rectangle will be drawn proportionally. E.G.
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.*;
public class DrawRect extends JPanel {
#Override
protected void paintComponent(Graphics g) {
int w = getWidth();
int h = getHeight();
g.drawRect(w/10, h/10, w/2, h/2);
}
/* A custom component should give the layout manager hints as to
its preferred size. */
#Override
public Dimension getPreferredSize() {
return new Dimension(200,200);
}
public static void main(String[] args) {
JFrame frame = new JFrame();
DrawRect panel = new DrawRect();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(panel);
frame.pack();
frame.setVisible(true);
}
}

frame.getContentPane().setLayout(new BorderLayout());
Insert the line before you add the component to the GUI.
You should study layoutmanagers, since it is a unique concept in Java.

Java Swing Scroll through drawing

Im trying to add a JScrollpane to my JPanel. The problem is that the scrollpane doesn't recognize that my drawing is outside the frame. So how do I add the JScrollpane correctly?
Main class:
public MainFrame() extends JFrame{
public MainFrame() {
Container container = getContentPane();
container(new BorderLayout());
container.add(new JScrollPane(new Drawing()));
setSize(1280,720);
setVisible(true);
}
Drawing class:
public class Drawing() extends JPanel {
#Override
protected void paintComponent(Graphics g) {
g.drawLine(10, 100, 30000, 10);
}
}

There are a couple of errors in your code, let's step through each of them:
You're extending JFrame, and you should avoid it, see: Extends JFrame vs. creating it inside the program for more information about it. You're actually not changing its behavior so it's not needed to extend it.
For your JScrollPane to show the whole line, you need to change your window's size to be the same size of your line (as shown in this answer by #MadProgrammer).
Related to point 2, avoid the use of setSize(...) and instead override getPreferredSize(): See Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing? for more information
You forgot to call super.paintComponent(...) method in your paintComponent() method.
Related to points 2, 3, you need to call pack() so Swing calculates the best preferred size for your component.
See this example:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
public class LongDraw {
private JFrame frame;
private Drawing drawing;
public static void main(String[] args) {
SwingUtilities.invokeLater(new LongDraw()::createAndShowGui);
}
private void createAndShowGui() {
frame = new JFrame(getClass().getSimpleName());
drawing = new Drawing();
JScrollPane scroll = new JScrollPane(drawing);
frame.add(scroll);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
class Drawing extends JPanel {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.drawLine(10, 100, 3000, 10);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(3000, 500);
}
}
}
Which produces something similar to this:

How to make a paint class that doesn't get called twice?

I wrote a paint class, and added the jpanel to the frame, but it's getting called twice for some reason, as I put a print statement inside the graphics method, and it printed it twice. The codes below are all the codes I have in my package.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Paint extends JPanel {
static Paint paint = new Paint();
#Override
public Dimension getPreferredSize() {
return new Dimension(500, 500);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
System.out.println("Hello");
}
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.add(paint);
frame.pack();
frame.setLocation(300, 300);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}

I tried your code and paintComponent it's not called twice every time. I don't think you have the control on when the JFrame is calling pack() when you call setVisible. It may depends on how your OS manage the windows.

Java - paintComponent won't show drawings on JPanel

I've gotten stuck trying to draw on a JPanel. I've learned how to create a JFrame, a JPanel, add event handlers, do the same in applets, and some other basic GUI development. But everytime I try to draw on a JPanel using the paintComponent(Graphics g) or paint(Graphics g) methods, nothing shows up. Buttons, as well as other JComponents, show up just fine. But g.drawString, g.drawRect, etc result in a blank JFrame window.
Here is my code:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.event.*;
public class Game extends JPanel {
public static void main(String[] args) {
new Game().game();
}
JPanel panel;
JButton button2;
JButton button;
public void game() {
panel = new JPanel();
button = new JButton("Ok");
panel.setLayout(new FlowLayout());
panel.add(button);
button2 = new JButton("Cancel");
JFrame frame = new JFrame("Game");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500,500);
frame.setResizable(false);
frame.add(panel);
frame.setVisible(true);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("hi",100,100);
g.fillRect(100,50,200,300)
}
}

The JPanel you're adding to your JFrame is a plain vanilla JPanel, not an instance of Game, your custom class that contains the paintComponent() method. YOu need to change that one line to
JPanel panel = new Game();
and you should see a difference immediately!
The instance of Game you create in main() isn't being used for anything, other than calling the game() method. You could use it, if you wanted, by doing this instead:
JPanel panel = this;
and then proceeding as before.

Issue with this simple code

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MyDrawPanel extends JPanel{
public void paintComponents(Graphics g){
g.setColor(Color.orange);
g.fillRect(20,50,100,100);
}
public static void main(String[] args){
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
frame.getContentPane().add(paintComponents(g));
frame.setVisible(true);
}
}
I think I should add something arguments in frame.getContentPane().add(paintComponents(g));.
I looked up Graphics class but I'm still struggling with it. What should be the parameter of it?

try this
public class MyDrawPanel extends JPanel{
MyDrawPanel()
{
setOpaque(true);
}
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.orange);
g.fillRect(20,50,100,100);
}
public static void main(String[] args){
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new MyDrawPanel());
frame.setBounds(10,10,500, 500);
frame.setVisible(true);
}
}

I'm no awt expert, but what I think you want to do is add a Canvas object to your content pane from the JFrame, then paint a Graphics object on it.

Okay, this is what I came up with:
public class MyDrawPanel extends JPanel
{
private static void createAndShowGUI()
{
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
MyDrawPanel panel = new MyDrawPanel();
panel.setOpaque(true);
frame.getContentPane().add(panel);
frame.setVisible(true);
}
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.setColor(Color.orange);
g.fillRect(20,50,100,100);
}
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run()
{
createAndShowGUI();
}
});
}
}
Notes:
There are several problems with your line frame.getContentPane().add(paintComponents(g));. What you said is "add to the content pane the result of calling paintComponents on g. Where did g come from? You can not used a variable until declared. The result of calling paintComponents is void which means the result cannot be used as an argument to a method. Presumably you had compiler errors.
I changed paintComponents to paintComponent. The former is used to control painting of subcomponents and in general should not be overridden.
Swing objects should not be created on the main thread. The details are complicated for a beginner (and described here in detail). Mostly you can just memorize the SwingUtilities.invokeLater pattern used above.