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Why my rectangle shape is so small in java graphics 2d

So I am new in java graphics and I am creating a program that will show a rectangle. But when I run my program it only show like a small box and not the rectangle. I don't really know why it is happening.
Here is my code:
import javax.swing.*;
public class GraphicsEditor{
public static void main(String[] args) {
JFrame frame = new JFrame();
JPanel panel = new JPanel();
Rectangle rectangle = new Rectangle();
frame.setSize(1280, 720);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.add(panel);
panel.add(rectangle);
}
}
This is my rectangle class:
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JPanel;
public class Rectangle extends JPanel implements Shape {
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2D = (Graphics2D) g;
g2D.fillRect(0, 0, 200, 130);
}
}
This is my shape interface:
import java.awt.*;
public interface Shape {
void paintComponent(Graphics g);
}

Here, try this
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;
public class GraphicsEditor {
public static void main(String[] args) {
JFrame frame = new JFrame();
Rectangle rectangle = new Rectangle();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(rectangle);
frame.pack();
// center frame on screen
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
class Rectangle extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2D = (Graphics2D) g;
g2D.fillRect(0, 0, 200, 130);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(500, 500);
}
}
A couple of things.
you don't need the interface.
unlike components, just painting a picture doesn't affect the layout manager, so the panel will be reduced to it's default size with out regard to any painting.
so you need to override getPreferredSize() in your JPanel.

As the comments said, you should set the preferred size of both your panel and rectangle to your desired size, and then pack the frame, like:
panel.setPreferredSize(new Dimension(500,500));
rectangle.setPreferredSize(new Dimension(500,500));
frame.pack();
Otherwise your LayoutManager (when not specified it defaults to FlowLayout) will handle your rectangle the way it wants. So another way would be learning about Layout Managers, and using your desired one.
As a side note, I would like to make some suggestions to your code. Remember, Swing is not thread safe, so place your code inside an invokeLater() call, such as:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
JPanel panel = new JPanel();
Rectangle rectangle = new Rectangle();
frame.setSize(1280, 720);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel.setPreferredSize(new Dimension(500,500));
rectangle.setPreferredSize(new Dimension(500,500));
frame.add(panel);
panel.add(rectangle);
frame.pack();
frame.setVisible(true);
}
});
Also, calling frame.setVisible(true) should be called after adding your components.

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);

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();
}
}

about drawing a Polygon in java

hi there i'm trying to improve myself about java2D and first of all i'm dealing with drawing polygons. However, i can not see the polygon on frame. I read some tutorials and examples but as i said i face with problems. here is the sample code of drawing a polygon;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Polygon;
import javax.swing.JFrame;
public class jRisk extends JFrame {
private JFrame mainMap;
private Polygon poly;
public jRisk(){
initComponents();
}
private void initComponents(){
mainMap = new JFrame();
mainMap.setSize(800, 600);
mainMap.setResizable(false);
mainMap.setVisible(true);
mainMap.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
int xPoly[] = {150,250,325,375,450,275,100};
int yPoly[] = {150,100,125,225,250,375,300};
poly = new Polygon(xPoly, yPoly, xPoly.length);
}
protected void paintComponent(Graphics g){
super.paintComponents(g);
g.setColor(Color.BLUE);
g.drawPolygon(poly);
}
/**
* #param args
*/
public static void main(String[] args) {
new jRisk();
}
}

JFrame does not have a paintComponent(Graphics g) method. Add the #Override annotation and you will get a compile time error.
1) Use JPanel and override paintComponent (you would than add JPanel to the JFrame viad JFrame#add(..))
2) Override getPreferredSize() to return correct Dimensions which fit your drawing on Graphics object or else they wont be seen as JPanel size without components is 0,0
3) dont call setSize on JFrame... rather use a correct LayoutManager and/or override getPrefferedSize() and call pack() on JFrame after adding all components but before setting it visible
4) Have a read on Concurrency in Swing specifically about Event Dispatch Thread
5) watch class naming scheme should begin with a capital letter and every first letter of a new word thereafter should be capitalized
6) Also you extend JFrame and have a variable JFrame? Take away the extend JFrame and keep the JFrame variable as we dont want 2 JFrames and its not good practice to extend JFrame unless adding functionality
Here is your code with above fixes (excuse picture quality but had to resize or it was going to 800x600):
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Polygon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class JRisk {
private JFrame mainMap;
private Polygon poly;
public JRisk() {
initComponents();
}
private void initComponents() {
mainMap = new JFrame();
mainMap.setResizable(false);
mainMap.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
int xPoly[] = {150, 250, 325, 375, 450, 275, 100};
int yPoly[] = {150, 100, 125, 225, 250, 375, 300};
poly = new Polygon(xPoly, yPoly, xPoly.length);
JPanel p = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLUE);
g.drawPolygon(poly);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(800, 600);
}
};
mainMap.add(p);
mainMap.pack();
mainMap.setVisible(true);
}
/**
* #param args
*/
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new JRisk();
}
});
}
}
As per your comment:
i am preparing a map which includes lots of polygons and yesterday i
used a JPanel over a JFrame and i tried to check if mouse was inside
of the polygon with MouseListener. later i saw that mouseListener gave
false responds (like mouse is not inside of the polygon but it acts
like it was inside the polygon). so i deleted the JPanel and then it
worked
Here is updated code with MouseAdapter and overridden mouseClicked to check if click was within polygon.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Polygon;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class JRisk {
private JFrame mainMap;
private Polygon poly;
public JRisk() {
initComponents();
}
private void initComponents() {
mainMap = new JFrame();
mainMap.setResizable(false);
mainMap.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
int xPoly[] = {150, 250, 325, 375, 450, 275, 100};
int yPoly[] = {150, 100, 125, 225, 250, 375, 300};
poly = new Polygon(xPoly, yPoly, xPoly.length);
JPanel p = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLUE);
g.drawPolygon(poly);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(800, 600);
}
};
MouseAdapter ma = new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent me) {
super.mouseClicked(me);
if (poly.contains(me.getPoint())) {
System.out.println("Clicked polygon");
}
}
};
p.addMouseListener(ma);//add listener to panel
mainMap.add(p);
mainMap.pack();
mainMap.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new JRisk();
}
});
}
}

JFrame does not extend JComponent so does not override paintComponent. You can check this by adding the #Override annotation.
To get this functionality extract paintComponent to a new class which extends JComponent. Don't forget to call super.paintComponent(g) rather than super.paintComponents(g).

Replace
protected void paintComponent(Graphics g){
super.paintComponents(g);
g.setColor(Color.BLUE);
g.drawPolygon(poly);
}
With
protected void paint(Graphics g){
super.paint(g);
g.setColor(Color.BLUE);
g.drawPolygon(poly);
}

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);
}
}