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Thread: paint only paints one obj

  1. #1
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    Default paint only paints one obj

    I'm just starting Java Swing and I want to create circles so I have a class that draws only circles and a constructor to set size and starting point, then in main, I create a new JFrame and add this obj. It's working, but when I try to add more circle objs to my JFrame, it doesn't show up. I know it's trivial...

    import javax.swing.*;
    import java.awt.*;
     
    public class Circle extends JPanel
    {
      private int starting_x;
      private int starting_y;
      private int width;
      private int height;
     
       public Circle(int x, int y,int w, int h)
       {
          this.starting_x = x;
          this.starting_y = y;
          this.width = w;
          this.height = h;
       }
     
      public void paintComponent(Graphics g)
      {
    	super.paintComponent(g);
     
    	Graphics2D g2d = (Graphics2D) g;
     
    	g2d.setColor(Color.black);
    	g2d.fillOval(start_x-1, start_y-1, width+2, height+2);
     
       }
    }

    //main in another file
    import javax.swing.*;
     
    public class Runner
    {
       public static void main(String[] args)
       {
          JFrame f = new JFrame();
          f.add( new Circle(100,100,34,34) );//this shows
          f.add( new Circle(300,305,34,34) );//this doesn't show though
          f.setVisible(true);
          f.setSize(1000,1000);  
       }
    }


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: paint only paints one obj

    You don't want to have multiple JPanels drawing single things at a time- you want to have a single JPanel drawing multiple things at a time.

    Think of a JPanel as a canvas. What you're doing is hanging up a canvas, drawing a circle on it, then hanging up another canvas right on top of the first one and drawing a circle on it- see why you can only see one circle at a time?

    (Technically I think that might be backwards- you might only be seeing the first thing you add, but the idea is the same.)
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