Java is not painting anything

[Hagelslag]

Im am trying to create a simple program that makes stars randomly apear on the screen.
When you use your mousewheel they have to change size and color. i dont see any errors left in the code but it just wont paint anything.

i hope some of you can help me with this, its important that i know at least the basics of java befor next week

import java.awt.*;

import javax.swing.JFrame;

public class Main extends JFrame
{
	public Main()
	{
		setLayout(new FlowLayout());
		setSize( 500, 500 );
		setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
		setTitle( "Starry sky" );
		setLocation( 200, 100 );
		setBackground(Color.BLUE);
		setVisible( true );
	}
	
	public static void main(String[] args)
	{
		new Main();
	}
}

import java.awt.*;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;
import java.util.Random;
import javax.swing.JPanel;

public class StarrySky extends JPanel implements MouseWheelListener
{
	private Star[] stars = new Star[100];
	Random location = new Random();
	private int size = 30;
	private Color colour;
	Star s;

	public StarrySky()
	{
		addMouseWheelListener( this );

		for (int index = 0; index < 100; index++)
		{
			int x = location.nextInt(600);
			int y = location.nextInt(600);

			if(index < 50)
			{
				stars[index] = new RedStar(x,y,size,colour);
			}
			else
			{
				stars[index] = new Star(x,y,size,colour);
			}

		}
	}

	public void paintcomponent(Graphics g)
	{
		super.paintComponent(g);
		super.setBackground(Color.blue);

		for(Star s : stars)
		{
			s.teken(g);
		}
	}

    public void mouseWheelMoved(MouseWheelEvent e)
    {
            s.Evolve();
            repaint();
    }
}

import java.awt.*;

public class Star 
{
	protected int x, y, size;
	protected Color colour;
	
	public Star(int x,int y,int size,Color colour)
	{
		this.x = x;
		this.y = y;
		this.size = size;
		this.colour = Color.YELLOW;
	}
	
	public void teken(Graphics g)
	{
		g.setColor(colour);
		g.fillRect(x, y, size, size);
	}
	
	public void Evolve()
	{
		if (size <= 100)
		{
			size = size + 2;
		}
	}
}

import java.awt.*;


public class RedStar extends Star
{
	public RedStar(int x,int y,int size,Color colour)
	{
		super(x, y, size, colour);
	}
	
	public void teken(Graphics g)
	{
		g.setColor(colour);
		g.fillRect(x, y, size, size);
	}
	
    private Color colour(int r, int g, int b)
    {
            return colour ;
           
    }
	
	public void Evolve()
	{
		 int r, g, b;
		 
         r = 245;
         g = 0;
         b = 0;

         if( r < 255)
         {
                 r +=2;
                 colour = colour(r,g,b);
                
         } 
	}
	
}

[JosAH]

You're not adding a StarrySky object to the content pane of your Main object as far as I can see.

kind regards,

Jos

[Hagelslag]

thanks for the reply,
I've had a feeling that the reason had to be something like that, but, could you please tell me how to add StarrySky to the Main class?
I'm trying a lot of diffrent things but it just doesn't work

[DarrylBurke]

I guess you need to start here: Trail: Creating a GUI With JFC/Swing (The Java™ Tutorials)

db

[jim829]

In your Main constructor, just do

StarrySky sky = new StarrySky();
add(sky);

There may be other issues though.

Regards,
Jim

[Hagelslag]

thanks for the help everyone.
I've added Jim's code to my main class but it still doesn't do anything.
something else i find strange is that i've set the background colour to blue but it's still gray.
Am i missing the code to paint anything?

EDIT:
i just noticed a typo in the paintComponent in StarrySky.
it is paintcomponent while it should be paintComponent.
now when i run my program i see a small blue square, it's not nearly finished but i can finally try more

[jim829]

Hi, that last error can be a common problem. It is advisable to put the @Override annotation before any method which is to be overridden. That way, if you get the signature wrong or mistype the method name, the compiler will flag it as an error. Otherwise, it just thinks you are creating a new method. If you are not familiar with annotations, try The Java™ Tutorials.

Regards,
Jim

[Hagelslag]

it seems like the little blue square has something to do with the super.setBackground in the StarrySky class.
sometimes i see a little bit of yellow inside the square. everything except the mousewheellistener seems to work.
does someone know how to fix this problem?

[Tolls]

I'm a bit rusty on this, but I don't see anything there that gives Swing any way of calculating how big the JPanel should be.
Looks to me like it's just gone for a default size (ie small).

Can I also suggest setting the background colour in the constructor?
Seems a bit pointless setting it everytime the paintComponent is called.

[jim829]

Ok, I did two things.

First, I gave StarrySky a size:

      setPreferredSize(new Dimension(500, 500));

Then I added pack() at the and of the main constructor.

Second, in the mouseWheelMoved method, you were referencing a local variable s that was not initialized. So I put a loop around it as shown.

@Override
   public void mouseWheelMoved(MouseWheelEvent e) {
      System.out.println(e.getClickCount());
      for (Star s : stars) {
         s.Evolve();
      }
      repaint();
   }

So now it shows movement but since I haven't tried to figure out what you want to do, that is all. One final note. It's subtle but it is documented in the Window API. If you do a

setLocationRelativeTo(null);

in the Main constructor it will center your frame on the screen.

Regards,
Jim

[Hagelslag]

thanks, this is great!
just a few tweaks and its prefect.
I'm currently reading those oracle java tutorials so that i wont have to bother all of you with my problems anymore

the @Override is a great tip too, i'll try to keep using that from now on.

Thank you all for helping me out!