Painting with a custom JComponent

[Garrett Rowe]

I'm trying to do some custom drawing via a JComponent. I can get the frame to show, but unfortunately I can't seem to get the graphics to appear. Here is a minimal version of my code.

import javax.swing.*;
import java.awt.*;

public class SwingTest {

   public static void main(String[] args) {
      final int WIDTH = 50;
      final int HEIGHT = 50;
      
      final JComponent rectComp = new JComponent() {
         @Override
         public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D)g;
            g2d.setColor(Color.BLACK);
            Rectangle r = new Rectangle(WIDTH, HEIGHT);
            g2d.fill(r);
         }
      };
      rectComp.setMinimumSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      rectComp.setPreferredSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      
      
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            JFrame frame = new JFrame("Test");
            frame.setLayout(new BorderLayout());
            frame.add(rectComp, BorderLayout.CENTER);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.pack();
            frame.setVisible(true);
         }
      });
   }
}

What do I need to do to get the rectangle to be drawn? Also, setting the minumum and preferred size of the JComponent seem to be to only way to get the JFrame to render in a non-minimized form. Are there better ways?

[Gregg Bolinger]

You fill the shape but you never draw the shape. You need to add g2d.draw(r)

As far as the size thing, you are calling pack(). If you want to control the size remove the call to pack() and call frame.setSize(...).

[Garrett Rowe]

Thanks for the tip about not calling pack() and calling setSize() on the JFrame, that's exactly what I was looking for. However even after calling draw(Shape) I'm still not getting an image rendered.

import javax.swing.*;
import java.awt.*;

public class SwingTest {

   public static void main(String[] args) {
      final int WIDTH = 50;
      final int HEIGHT = 50;
      
      final JComponent rectComp = new JComponent() {
         @Override
         public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D)g;
            g2d.setColor(Color.BLACK);
            Rectangle r = new Rectangle(WIDTH, HEIGHT);
            g2d.draw(r);
            g2d.fill(r);
         }
      };
      rectComp.setMinimumSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      rectComp.setPreferredSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      
      
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            JFrame frame = new JFrame("Test");
            frame.setLayout(new BorderLayout());
            frame.add(rectComp, BorderLayout.CENTER);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
            frame.setSize(WIDTH * 2, HEIGHT * 2);
         }
      });
   }
}

[Gregg Bolinger]

You aren't telling the system where to draw the rectangle.

Rectangle r = new Rectangle(WIDTH, HEIGHT, 10, 10)

[Garrett Rowe]

Thanks for the help Gregg. The problem was actually something different, and a little wierder to me. It wasn't that the image wasn't getting rendered, it had to do with the WIDTH and HEIGHT constants. I added a some logging statements and got this:

import javax.swing.*;
import java.awt.*;

public class SwingTest {

   public static void main(String[] args) {
      final int WIDTH = 50;
      final int HEIGHT = 50;
      
      final JComponent rectComp = new JComponent() {
         @Override
         public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D)g;
            g2d.setColor(Color.BLACK);
            Rectangle r = new Rectangle(WIDTH, HEIGHT);
System.out.println(r);
            g2d.draw(r);
            g2d.fill(r);
         }
      };
      rectComp.setMinimumSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      rectComp.setPreferredSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      
      
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            JFrame frame = new JFrame("Test");
            frame.setLayout(new BorderLayout());
            frame.add(rectComp, BorderLayout.CENTER);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
            frame.setSize(WIDTH * 2, HEIGHT * 2);
         }
      });
   }
}

Output:

java.awt.Rectangle[x=0,y=0,width=1,height=2]

But this produces the output I expected:

import javax.swing.*;
import java.awt.*;

public class SwingTest {

   public static void main(String[] args) {
      final int WIDTH = 50;
      final int HEIGHT = 50;
      
      final JComponent rectComp = new JComponent() {
         @Override
         public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D)g;
            g2d.setColor(Color.BLACK);
            Rectangle r = new Rectangle(50, 50);
System.out.println(r);
            g2d.draw(r);
            g2d.fill(r);
         }
      };
      rectComp.setMinimumSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      rectComp.setPreferredSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      
      
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            JFrame frame = new JFrame("Test");
            frame.setLayout(new BorderLayout());
            frame.add(rectComp, BorderLayout.CENTER);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
            frame.setSize(WIDTH * 2, HEIGHT * 2);
         }
      });
   }
}

Output:

java.awt.Rectangle[x=0,y=0,width=50,height=50]

Can anyone figure out why this is?

[Gregg Bolinger]

Not sure of the EXACT issue but looking at the API docs, WIDTH and HEIGHT are fields inherited from interface java.awt.image.ImageObserver.

[Garrett Rowe]

I just saw the same thing. I guess that's one more reason enum types are superior to int constants in new code.

[Rob Spoor]

Gregg Bolinger wrote:Not sure of the EXACT issue but looking at the API docs, WIDTH and HEIGHT are fields inherited from interface java.awt.image.ImageObserver.

We have a winner!

Garrett, if you're always drawing the same rectangle, why not create the rectangle outside of the component?

import javax.swing.*;
import java.awt.*;

public class SwingTest {

   public static void main(String[] args) {
      final int WIDTH = 50;
      final int HEIGHT = 50;

      final Rectangle rectangle = new Rectangle(WIDTH, HEIGHT);
      final JComponent rectComp = new JComponent() {
         @Override
         public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D)g;
            g2d.setColor(Color.BLACK);
            g2d.draw(rectangle);
            g2d.fill(rectangle);
         }
      };
      rectComp.setMinimumSize(new Dimension(WIDTH * 2, HEIGHT * 2));
      rectComp.setPreferredSize(new Dimension(WIDTH * 2, HEIGHT * 2));


      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            JFrame frame = new JFrame("Test");
            frame.setLayout(new BorderLayout());
            frame.add(rectComp, BorderLayout.CENTER);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
            frame.setSize(WIDTH * 2, HEIGHT * 2);
         }
      });
   }
}