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Why are Graphics2D rectangles not displayed?

I need to be able to display filled rectangles for the program i am creating, however the following code produces the following GUI with only the black text 'test' after calling start then change, could anyone explayin why please?
package core;
import java.awt.Color;
import java.awt.Graphics2D;
import javax.swing.JFrame;
#SuppressWarnings("serial")
public class GUI extends JFrame{
private Graphics2D g;
private int[][][] clickable;
public void start(){
this.setSize(500, 500);
this.setTitle("Placeholder");
this.setVisible(true);
g = (Graphics2D) this.getGraphics();
}
public void change(String[] fields, int type[], boolean forwards){
g.setColor(new Color(28,35,57));
g.drawRect(0, 0, 100, 100);
g.drawRect(50, 50, 150, 150);
g.fillRect(0, 0, 100, 100);
g.drawString("test", 300, 300);
}
}
And here is what it looks like ..

Drawing on Swing components (like JFrame) works only in onPaint event.
The event can be fired using repaint() method.
This event fires automatically when frame needs to be painted.
To implement this event behavior override paint() method.
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
public class GUI extends JFrame{
private Graphics2D g;
public void start(){
this.setSize(500, 500);
this.setTitle("Placeholder");
this.setVisible(true);
}
public void change(){
g.setColor(new Color(28,35,57));
g.drawRect(0, 0, 100, 100);
g.drawRect(50, 50, 150, 150);
g.fillRect(0, 0, 100, 100);
g.drawString("test", 300, 300);
}
public void paint(Graphics g2d){
g = (Graphics2D) g2d;
change();
}
public static void main(String[] args){
GUI frame = new GUI();
frame.start();
}
}

Paint not showing up

I am using a JFrame and a pane and trying to draw a simple square.
My painting is not showing up. I made I set the color to black so it should be visible.
Code:
package W2;
import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import javax.swing.*;
public class W2 {
JFrame frame = new JFrame("W2");
public W2(){
Container pane = new Container();
frame.setContentPane(pane);
frame.setSize(750,500);
frame.setLocationRelativeTo(null);
frame.setResizable(false);
frame.setVisible(true);
}
public void paint(Graphics g){
g.setColor(Color.BLACK);
g.fillRect(50, 50, 50, 50);
}
public static void main(String args[]){
new W2();
}
}

The paint method won't be called because it's not part of a object that can be painted.
See Performing Custom Painting for details about how painting is done in Swing
For example...
frame.setContentPane(new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK);
g.fillRect(50, 50, 50, 50);
}
});

Set gradient direction in swing

I have been trying to draw lines in swing and get some laser-like effects using gradients. I want to apply the gradient on the line's width (ex: a red line core fading to orange on the edges). The problem is when I draw at an angle, I want to somehow apply the same angle to the gradient.
public void paintComponent(Graphics g) {
Graphics2D en = (Graphics2D) g;
GradientPaint gp = new GradientPaint(25, 25, Color.red, 15, 25,
Color.orange, true);
en.setPaint(gp);
en.setStroke(new BasicStroke(4.0F));
en.drawLine(10, 10, 800, 600);
}

One easy trick to get away with this, is to call setTransform() on the Graphics2D. This will do for you the rotation of both the line and the gradient at once. If you don't want to do this, then you will have to rotate the gradient itself (so basically pt1 and pt2 of the Gradient manually, ie, you need to compute them according to the rotation you have applied to your line).
Here is a small example illustrating my first idea. Just slide the ticker at the bottom to watch the line (and the gradient) rotate around the center of the panel:
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class TestPanel extends JPanel {
private double angle = 0;
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D en = (Graphics2D) g;
AffineTransform tf = AffineTransform.getTranslateInstance(-getWidth() / 2, -getHeight() / 2);
tf.preConcatenate(AffineTransform.getRotateInstance(Math.toRadians(angle)));
tf.preConcatenate(AffineTransform.getTranslateInstance(getWidth() / 2, getHeight() / 2));
en.setTransform(tf);
GradientPaint gp = new GradientPaint(25, 25, Color.red, 15, 25, Color.orange, true);
en.setPaint(gp);
en.setStroke(new BasicStroke(4.0F));
en.drawLine(400, 400, 600, 600);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(800, 800);
}
public void setAngle(double angle) {
this.angle = angle;
repaint();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
final TestPanel panel = new TestPanel();
final JSlider slider = new JSlider(0, 360);
slider.addChangeListener(new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
panel.setAngle(slider.getValue());
}
});
slider.setValue(0);
frame.add(panel);
frame.add(slider, BorderLayout.SOUTH);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
});
}
}

Drawing a bordered path with sharp corners in Java

I am working on an application that displays GPS tracks on a map. I want to draw the track as a colored path of arbitrary thickness. I found the GeneralPath class which seems to do just what I want. However, I want the colored path to also have a black border. I couldn't find anything about how to add a border to a path, so I came up with a quick hacky solution of drawing a thick black path first, and then drawing a thin colored path on top.
SSCCE:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.GeneralPath;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class PathBorder {
private JFrame frame;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
PathBorder window = new PathBorder();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
public PathBorder() {
initialize();
}
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 450, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel() {
protected void paintComponent(Graphics g) {
GeneralPath path;
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setStroke(new BasicStroke(5.5f));
g2d.setColor(Color.BLACK);
path = new GeneralPath();
path.moveTo(0, 0);
path.lineTo(100, 100);
path.lineTo(200, 100);
path.lineTo(100, 80);
g2d.draw(path);
g2d.setStroke(new BasicStroke(3));
g2d.setColor(Color.YELLOW);
g2d.draw(path);
}
};
frame.setBackground(Color.CYAN);
frame.add(panel);
}
}
Here is a pic (taken from the SSCCE) to highlight my problem. See the red circle below, notice how the outside border has a gap in it. I want that gap to be filled in so the border is continuous.
Here are some actual screenshots from my app of a real track:
If you look closely at the sharp hairpin turn in the lower right of the track, you'll see that the border gets lost briefly... the detailed pic below makes it more clear.
I am not sure exactly how to fix this, but I'm open to suggestions, either keeping with the GeneralPath strategy, or using a different idea entirely.

Experiment with the cap and join parameters for a better effect. E.G.
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.GeneralPath;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class PathBorder {
private JFrame frame;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
PathBorder window = new PathBorder();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
public PathBorder() {
initialize();
}
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 450, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel() {
GeneralPath path;
protected void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
BasicStroke s = new BasicStroke(
5.5f,
BasicStroke.CAP_ROUND,
BasicStroke.JOIN_ROUND);
g2d.setStroke(s);
g2d.setColor(Color.BLACK);
if (path==null) {
path = new GeneralPath();
path.moveTo(0, 0);
path.lineTo(100, 100);
path.lineTo(200, 100);
path.lineTo(100, 80);
}
g2d.draw(path);
g2d.setStroke(new BasicStroke(3));
g2d.setColor(Color.YELLOW);
g2d.draw(path);
}
};
frame.setBackground(Color.CYAN);
frame.add(panel);
}
}

Paint method java - Rectangle with outline

I want to create a wall with a blue line outline and black filling. I have only a blue wall now and I tried a couple of the Graphics methods but wasn't working.
public void paint(Graphics g) {
g.setColor(Color.blue);
g.fillRect(x, y, size, size);
}

Use Graphics#drawRect to draw the outline: -
g.setColor(Color.black);
g.fillRect(x, y, size, size);
g.setColor(Color.blue);
g.drawRect(x, y, size, size);

First, override paintComponent, not paint. Second, there's no need to re-invent the wheel like that. Instead, use an existing Swing component (e.g. JPanel),
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Main
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI()
{
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new FlowLayout());
frame.add(getWallComponent());
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private static JPanel getWallComponent()
{
JPanel panel = new JPanel();
panel.setBackground(Color.black);
panel.setBorder(BorderFactory.createLineBorder(Color.blue, 5));
panel.setPreferredSize(new Dimension(200, 200)); // for demo purposes only
return panel;
}
}

Just paint another rectangle over the blue one, smaller than the blue one, like below
public void paint(Graphics g) {
g.setColor(Color.blue);
g.fillRect(x, y, size, size);
g.setColor(Color.black);
g.fillRect(x-width/2,y-width/x,size-width,size-with);
}

package painting;
import java.awt.*;
import javax.swing.*;
public class RectangleOutline extends JPanel {
int x = 100;
int y = 200;
public void paintComponent(Graphics g) {
super.paintComponent(g);
outline(g);
}
public void outline(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(new Color(255, 0, 0));
g2.fillRect(x, y, 30, 30);
g2.setStroke(new BasicStroke(5));
g2.setColor(new Color(0, 0, 0));
g2.drawRect(x, y, 30, 30);
}
public static void main(String[] args){
JFrame f = new JFrame();
RectangleOutline graphics = new RectangleOutline();
f.add(graphics);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
f.setSize(400, 400);
}
}