Question

Trying to work with basic swing on Java keeps giving me issues.
When the JFrame is created by the runtime, none of the components are drawn initially, you have to resize the window to invoke paint() apparently? Is there a simple fix to this that I’m missing?

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

public class LabTen extends JFrame{

    int x, y;

    public LabTen(){
        this.setSize(200,200);
        this.setVisible(true);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.getContentPane().add(new Board()); //do this in the constructor    
    }

    public static void main(String[] args){
        LabTen one = new LabTen();
        one.repaint();
    }       
}
//mouseListener has more things when we're going in and out so you should have it too
//write on the component or pannel, not the frame
class Board extends JComponent implements MouseListener, MouseMotionListener{

    int mouseX, mouseY;

    public Board(){
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    public void mouseMoved(MouseEvent e){           
        this.mouseX = e.getX();
        this.mouseY = e.getY();
        this.repaint(); 
    }

    public void mouseDragged(MouseEvent e){
        //do nothing...
    }

    public void mouseClicked(MouseEvent e){         
    }

    public void mouseEntered(MouseEvent e){         
    }

    public void mouseExited(MouseEvent e){
    }

    public void mousePressed(MouseEvent e){         
    }

    public void mouseReleased(MouseEvent e){
    }

    public void paintComponent(Graphics g){
        //g.drawString("(" + this.mouseX + ", " + this.mouseY +  ")", this.mouseX,this.mouseY);
        //this uses the default way
        // g.drawLine(this.getWidth()/2, this.getHeight()/2, this.mouseX, this.mouseY);

        double distance = Math.sqrt(Math.pow(this.mouseX - this.getWidth()/2, 2) + Math.pow(this.mouseY - this.getHeight()/2, 2));          
        int centerX = this.getWidth()/2;
        int centerY = this.getHeight()/2;

        for(int i = 0; i < 20; i++){
            double distanceX = 
            g.drawLine(centerX, centerY, (centerX))
        }           
    }
}

Answer 1

You are doing it completely the wrong order. Do it this way:

1. Add the component

   this.add(new Board());
   

2. Set the preferred size

   this.setPreferredSize(new Dimension(200, 200));
   

3. Pack the frame

   this.pack();
   

4. Set the frame visible.

   this.setVisible(true);
   

Of course, this is your JFrame.