Develop Reference

The method is undefined for the type JPanel

So I am trying to create a simple program that prints out a rectangle but I am having this problem and I don't know how to fix it. Here is my code:
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.*;
public class GraphicsEditor extends JPanel{
public void drawShape(Graphics g) {
super.drawShape(g);
g.setColor(Color.BLUE);
g.drawRect(100, 100, 120, 150);
}
public static void main(String[] args) {
JFrame frame = new JFrame();
GraphicsEditor ga = new GraphicsEditor();
frame.setSize(1280, 720);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(ga);
}
}
The error is when I am trying to add the super in here:
public void drawShape(Graphics g) {
super.drawShape(g);
g.setColor(Color.BLUE);
g.drawRect(100, 100, 120, 150);
}

A JPanel has no drawShape(Graphics) method, so calling the 'super' method makes no sense. When you think you're overriding a method, be sure to add the #Override notation to get a compiler warning when the method is incorrectly spelled, uses the wrong arguments, or is just entirely non-existent (as is the case here).
The correct way to go about this is to override the paintComponent method, call the (existing) super method, then immediately call the drawShape method with the Graphics instance provided to the paintComponent method.
This is the result when the GUI is shrunk down:
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.*;
public class GraphicsEditor extends JPanel {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
drawShape(g);
}
// #Override // does NOT override an existing method!
public void drawShape(Graphics g) {
//super.drawShape(g);
g.setColor(Color.BLUE);
g.drawRect(100, 100, 120, 150);
}
public static void main(String[] args) {
JFrame frame = new JFrame();
GraphicsEditor ga = new GraphicsEditor();
frame.setSize(280, 200);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(ga);
}
}

Why paintComponent doesn't work?

I'm having issues with this code. For some reason, paintComponent(Graphics g) simply doesn't work and there doesn't seem to be an answer how to force it to. This is my code:
import javax.swing.JFrame;
public class Robotron extends JFrame
{
public Robotron ()
{
//add(this); This one gave me an error
setSize(800, 600);
new TestFrame();
setVisible(true);
}
public static void main(String [ ] args)
{
new Robotron();
}
and this is my TestFrame class that has the paintComponent function:
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;
public class TestFrame extends JPanel
{
public void paintComponent(Graphics g)
{
g.setColor(Color.BLACK);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(Color.YELLOW);
g.fillRect(100, 100, 10, 30);
System.out.println("Abdullah Paint");
}
public TestFrame()
{
setFocusable(true);
repaint();
}
}
What can I do in order to make paintComponent actually play. What I get in the end is just an empty JFrame, with no running of the System.out.println thingy.
Thanks a whole lot, been tackling this for a long time.

You're not adding anything to the JFrame, because of this
//add(this);
Here, you were trying to add the component to itself, which is not going to fly.
Instead, you need to add the TestFrame instance to the Frame.
add(new TestFrame());
setSize(800, 600);
setVisible(true);

You need to add the panel to the frame:
public Robotron ()
{
//add(this); This one gave me an error
setSize(800, 600);
add(new TestFrame());
setVisible(true);
}

As mentioned by others, you need to add the panel to the frame:
public Robotron() {
add(new TestFrame());
setSize(800, 600);
setVisible(true);
}
As not mentioned by others, you need to call super.paintComponent(g) the first thing in your overridden method:
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(Color.YELLOW);
g.fillRect(100, 100, 10, 30);
System.out.println("Abdullah Paint");
}
Notes:
Don't call repaint() in the constructor. At best it does nothing.
Don't call setSize(...) for the frame, instead call pack(). You will need to override the getPreferredSize method in your panel for this.

Set Oval throwing error

I am currently working on a project, I get this error Java.lang.NullPointerException, I undrestand that this error happen when you try to refer to a null object instance, but what I do not know, is how I can fix it.
This is my code:
public void paint(Graphics g) {
g.setColor(Color.red);
g.drawOval(150, 150, 10, 10);
}
/** Main Method **/
public static void main(String [] args) {
Run run = new Run();
run.paint(null);
}
Please help me with a solution and also explain it, so that I learn it. Many thanks in advance. Andre

You may not pass null to your paint method! Here is a small example how to do it:
import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.JFrame;
class MyCanvas extends JComponent {
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawOval (10, 10, 200, 200);
}
}
public class DrawOval {
public static void main(String[] a) {
JFrame window = new JFrame();
window.setBounds(30, 30, 300, 300);
window.getContentPane().add(new MyCanvas());
window.setVisible(true);
}
}

You almost never call paint methods (including paintComponent) directly as this is what the JVM should be doing.
Don't override the paint(Graphics g) method of a JComponent or JComponent derived class such as a JPanel if you can avoid it. This method, paint, is responsible for not only painting the component but also its borders and its child components, and if not done carefully, overriding this method will not infrequently result in unwanted side effects.
Later when you want to do graphics animation, overriding paint(Graphics g) will result in jerky graphics since it does not do double buffering by default.
By overriding the paintComponent(Graphics g) method instead you fix these issues.
Don't forget to call the super's paintComponent(g) method in your override to erase any unwanted previously drawn images.
Read the Swing Graphics tutorials, both the basic and advanced tutorials. Links at the bottom.
Better code:
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.JFrame;
#SuppressWarnings("serial")
public class MyBetterCanvas extends JComponent {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawOval(10, 10, 200, 200);
}
public static void main(String[] a) {
MyBetterCanvas canvas = new MyBetterCanvas();
canvas.setPreferredSize(new Dimension(300, 300));
JFrame window = new JFrame("My Better Canvas");
window.getContentPane().add(canvas);
window.setLocationByPlatform(true);
window.pack();
window.setVisible(true);
}
}
Better Still:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Paint;
import java.awt.RenderingHints;
import javax.swing.JComponent;
import javax.swing.JFrame;
#SuppressWarnings("serial")
public class MyBetterStillCanvas extends JComponent {
private static final int PREF_W = 500;
private static final int PREF_H = 500;
private static final int OVAL_X = 10;
private static final int OVAL_Y = OVAL_X;
private static final Paint BG_PAINT = new GradientPaint(0, 20,
Color.black, 20, 0, Color.darkGray, true);
private static final Paint FILL_PAINT = new GradientPaint(0, 0,
Color.blue, 20, 20, Color.red, true);
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
// to smooth out graphics
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
// let's draw something funky
g2.setPaint(BG_PAINT);
g2.fillRect(0, 0, getWidth(), getHeight());
g2.setPaint(FILL_PAINT);
// avoid use of "magic" numbers
g.fillOval(OVAL_X, OVAL_Y, getWidth() - 2 * OVAL_X, getHeight() - 2
* OVAL_Y);
}
// a cleaner way to set the preferred size of a component
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
public static void main(String[] a) {
JFrame window = new JFrame("My Better Canvas");
window.getContentPane().add(new MyBetterStillCanvas());
window.setLocationByPlatform(true);
window.pack();
window.setVisible(true);
}
}
Which displays as:
Tutorials:
Java Tutorials, Really Big Index
Java Swing Tutorials
Basic Swing Graphics Tutorial: Lesson: Performing Custom Painting
More Advanced Graphics Article: Painting in AWT and Swing

You are not doing it the right way. In order to use graphics in java you need to build upon Swing/AWT components. Currently you are passing Graphics as null.
run.paint(null);
You need to implement this using JFrame and other swing components.

Since you are sending null to paint, Graphics g contains null (points to nowhere).
Then inside paint(...) you call setColor(...) on g, which is null. null.setColor(...) causes NullPointerException.

Graphics dont appear

Whatever I do, I can not display rectangle/line/oval on the screen. I checked other sources where they paint graphics, but when I even execute those codes, I don't get any graphics displayed on the windows. Below is the example from the text book.
import java.awt.*;
import javax.swing.*;
class PlotGraph
{
public static void main (String [] args) {
JFrame win;
Container contentPane;
Graphics g;
win = new JFrame("testing");
win.setSize(300,200);
win.setLocation(100,100);
win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
win.setVisible(true);
contentPane = win.getContentPane();
g = contentPane.getGraphics();
g.drawRect(10, 30, 50, 50);
}
}

Ouch. You should change your text book then. First of all, all the accesses to Swing components must be done in the event dispatch thread.
Second, you should not get the graphics of a component and paint on it. Instead, you should extend a JComponent or JPanel, override its paintComponent(Graphics) method, and paint using the Graphics object passed as argument (and which is in fact a Graphics2D instance).

That's not how graphics work in Swing.
You need to add a component to your frame, not just draw on it. You never want to draw directly on the frame. The reason why it's not doing anything is because your drawing code is being overridden.
If you want your component to have custom drawing code, make a subclass of JComponent and override the paintComponent(Graphics) method. An example of how you should do this is as follows:
import java.awt.*;
import javax.swing.*;
class PlotGraph {
public static void main(String[] args) {
JFrame win;
win = new JFrame("testing");
win.setSize(300, 200);
win.setLocation(100, 100);
win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
win.setVisible(true);
win.setContentPane(new MyComponent());
}
}
class MyComponent extends JComponent {
#Override
public void paintComponent(Graphics g) {
g.drawRect(10, 30, 50, 50);
}
}
I would highly encourage you to check out the Java GUI tutorial online.

Can not draw oval on a JPanel

I have a JFrame created with GUI builder of Netbeans, which contains a JPanel only. I have created a method getPanel for getting a reference to this JPanel:
public class ShowDrawings extends JFrame {
public ShowDrawings() {
initComponents();
}
public JPanel getPanel(){
return panel;
}
private JPanel panel;
}
In my main function I am doing:
public class Main {
public static void main(String[] args){
ShowDrawings sd = new ShowDrawings();
sd.setSize(800, 600);
Graphics g = sd.getPanel().getGraphics();
g.setColor(Color.BLACK);
g.drawOval(400, 300, 50, 50);
sd.getPanel().paint(g);
sd.repaint();
sd.setVisible(true);
}
}
But it does not draw anything. Please help me.
I have looked some related questions but they are all suggesting extending JPanel and overriding its paint method. But I did not want to do that way.
Thanks.

I have looked some related questions but they are all suggesting
extending JPanel and overriding its paint method. But I did not want
to do that way
You should not override JPanel paint() method, rather paintComponent(..). This is best practice and should be done if you want code that will not produce anomalies. Also doing it in your current approach (as you have seen) makes creating persistent drawings a lot harder as they are wiped away on repaint()
Rather extend JPanel and override paintComponent(Graphics g) not forgetting to call super.paintComponent(g) as first call in overridden paintComponent(..) method. Also dont forget to override getPreferredSize() of JPanel so that we can return correct dimensions and pack() may be called on JFrame (+1 to #mKorbels comment):
Here is some example code:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Test {
public Test() {
initComponents();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Test();
}
});
}
private void initComponents() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel testPanel = new JPanel() {
#Override
protected void paintComponent(Graphics grphcs) {
super.paintComponent(grphcs);
Graphics2D g2d = (Graphics2D) grphcs;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setColor(Color.GREEN);
//g2d.drawOval(10,10,100,100);//I like fill :P
g2d.fillOval(10,10,100,100);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(150, 150);
}
};
frame.add(testPanel);
frame.pack();
frame.setVisible(true);
}
}

The first time you repaint() your ShowDrawings sd frame anything you've painted like this (sd.getPanel().getGraphics().drawOval(...)) would be erased by the original JPanel#paintComponent() method.
As Andrew Thompson has written:
Do not use Component.getGraphics(). Instead, subclass and override the paint() (AWT), or paintComponent() (Swing) method.
Component.getGraphics() simply can't work. Java uses a callback mechanism for drawing graphics. You are not supposed to "push" graphics information into a component using getGraphics(). Instead you are supposed to wait until Java calls your paint()/paintComponent() method. At that moment you are supposed to provide the Component with the drawings you would like to do.
If you're just checking/debugging something you could even do something like this:
class Test {
private JPanel panel = new JPanel() {
public void paintComponent(Graphics g) {
g.setColor(Color.BLACK);
g.drawOval(400, 300, 50, 50);
}
};
}