Question

I’m working on my first java project, and I’ve been confounded. This opens a dialog box to get a number from 0-255, checks that it is an integer and that it is in range, then uses the int to make a shade of gray for the background of a graphic applet. I have it doing everything it’s supposed to! But it doesn’t draw the applet. The program is terminated after the last time JOptionPane is called.

import javax.swing.JApplet;
import javax.swing.JOptionPane;
import java.awt.Graphics;
import java.awt.Color;

@SuppressWarnings("serial")
public class DrawingShapes extends JApplet
{
  private Shade shade = new Shade();
  private void getColor()
  {
    int rgb = 0;
    boolean useful = false;
    String number = JOptionPane.showInputDialog("Make this easy for me.\n"
    + "Type an integer between 0 and 255");
    {
      try
      {
        rgb = Integer.parseInt(number);
        if (rgb > 0 && rgb < 255)
        {
          useful = true;
          shade.setColor(rgb);
        }
        else
        {
          useful = false;
          number = JOptionPane.showInputDialog( null, "\"" + number + "\""
          + " is not between 0 and 255!\n"
          + "Lrn2 be doin' it right!" );
        }
      }
      catch (NumberFormatException nfe)
      {
      number = JOptionPane.showInputDialog(null, "\"" + number + "\""
      + " is not an integer!\n"
      + "Lrn2 be doin' it right!");
      }
    }
    if (useful)
    {
      JOptionPane.showMessageDialog(null, rgb + " will be the shade of gray.");
      //WHEN this message is closed, the program seems to quit.
      //System.exit(0);
    }
  }
  public static void main(String[] args)
  {
    new DrawingShapes().getColor();
  }
  public class Shade
  {
    private int color;
    public void setColor(int col)
    {
      color = col;
      System.out.println("color: " + color);
      System.out.println("col: " + col); //IT prints these lines....
    }
    public void paint (Graphics g) //Everything after this is sadly ignored.
    {
      int size = 500;
      setSize(size, size);
      int rgb = color;
      Color gray = new Color(rgb,rgb,rgb);
      setBackground(gray);
      System.out.println(rgb + " This should be the third time");
      g.drawOval(0, 0, size, size);
    }
  }
}

I cannot figure out what is wrong with ‘public void paint (Graphics g)’, but it doesn’t cause anything to happen. I’ll welcome correction from anyone, I’m sure I’ve made a laughable mistake because I’m not quite comfortable with the language…

Answer 1

This isn’t an applet program — yes, it extends JApplet, but there’s no init method and instead you have a main method — a method that will not be called in an applet program. Please go through the JApplet Tutorial first before doing anything else.

Other suggestions:

• Again you’ll need a proper init() override.
• Don’t draw directly in a JApplet or any top level Window component.
• Instead draw in the paintComponent(...) method of a JPanel that is shown in the JApplet.
• Don’t set background colors or change the GUI’s state in the paint(...) or paintComponent(...) method.
• You’ll want to call the super.paintComponent(...) method inside of your paintComponent(...) method override, and often this is the first method call of your method.
• Also you’ll want to read the Swing Graphics tutorial on the same site as it will help you a lot.
• If instead of an applet you wish to create a desk-top application, then place your your attack will be a little bit different in that you won’t have an init() method override, you will need a main method, and you’ll put your components into a JFrame as your top-level Window.
• To get better help, post less excuses and apologies in your question (I’ve deleted most) and instead focus on providing helpful information in as clear a manner as possible. We aren’t interested in your situation as much as we are interested in helping solve your problem, so please help us help you.

Luck!