Question

I am having a problem with my java code. I’m trying to make it so the top left quadrant produces a set number of lines input by a user through JOption Pane which are in random colors and in random positions. The programs builds successfully but it does not produce the number of lines the user input, nor does it set a random color (This it at the very bottom of my code). Can someone please explain how to fix this problem? Thanks very much.
Edit: fixed the curve braces but still will not work.
Edit: Everything works now except the random colors

import javax.swing.*;   //for JFrame
import java.awt.*;      //for Graphics and Container
import java.util.Random;
import javax.swing.JOptionPane;

// other import statements here


public class RandomGraphics
{
    // constants are used to draw the grid, and for you to put shapes in the grid
    public static final int MIDX = 400;
    public static final int MIDY = 300;
    public static final int MAXX = 799;
    public static final int MAXY = 599;
    public static final int COLOR = (int) (Math.random() * 256);

    // make another constant for the color value that will
    // be used to generate a random color

    public static void main( String[] args )throws InterruptedException
    {
        //*** This next section sets up the graphics window.
        //*** You are not required to understand it
        Container contentPane;
        Graphics g;
        JFrame win = new JFrame("Random Graphics");
        win.setSize(825,650);
        win.setLocation(0,0);
        win.setVisible(true);
        win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        contentPane = win.getContentPane();
        contentPane.setBackground(Color.white);
        g = contentPane.getGraphics();
        Thread.sleep(50);
        //*** done setting up graphics window


        // Draws Grid - DO NOT CHANGE
        // After you use JOptionPane to get the number of lines, you can move this
        // section of code to just after that, so the lines will not disappear
        g.drawRect(0,0,MAXX+1,MAXY+1);
        g.drawLine(0,MIDY,MAXX,MIDY); // horizontal line
        g.drawLine(MIDX,0,MIDX,MAXY); // vertical line


        // Create Random object
        Random r = new Random();



        // Top left quadrant:


        // Use a JOptionPane to ask the user to enter the number of lines 1 to 100.
        int count = 0;
        do
        {

            String morelines = JOptionPane.showInputDialog("Enter a number of lines between 1 to 100");
            count = Integer.parseInt(morelines);
        }
        while(count > 100 || count < 1);


        for(int i = 1; i >= count; i++)
{
                g.setColor(new Color (r.nextInt(COLOR), r.nextInt(COLOR), r.nextInt(COLOR)));
                g.drawLine(r.nextInt(MIDX), r.nextInt(MIDY), r.nextInt(MIDX), r.nextInt(MIDY));
}

Answer 1

g = contentPane.getGraphics();

Graphics objects are not persistent, the programmer needs to draw the GUI to them when asked to do so. For tips, see the Performing Custom Painting Lesson of the tutorial.

---

Beside the ‘always include curly braces around loops advice’, note..

for(int i = 1; i >= count; i++)

Should be..

for(int i = 1; i <= count; i++)

But don’t ignore the advice about custom painting. The app. will not render reliably until that is fixed.