Thread: Problem with paintComponent...?

Hello !
Here is my Code:
LineDrawV2

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;
import javax.swing.filechooser.FileNameExtensionFilter;
 
public abstract class LineDrawV2 extends JFrame implements ActionListener{
    public static int i = 0;
    public static Double[] storeCoordinates;
    public static JFrame frame1 = new JFrame();
 
    private static final long serialVersionUID = 1L;
    private static Graphics Graphics;
 
    public static void main(String[] args)  {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
            Logger.getLogger(LineDrawV2.class.getName()).log(Level.SEVERE, null, ex);
        } 
 
 
        frame1.setSize(800, 600);
        frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame1.setLocationRelativeTo(null);
        frame1.setTitle("Line Draw 2");
        //frame1.getContentPane().setLayout(null);
 
 
 
        final JFileChooser martin = new JFileChooser();
        martin.setAcceptAllFileFilterUsed(false);
        martin.setFileFilter(new FileNameExtensionFilter("Text Files", "txt", "rtf"));
 
 
 
        JMenuBar mb = new JMenuBar();
        frame1.setJMenuBar(mb);
        JMenu filemb = new JMenu("File");
        mb.add(filemb);
        JMenuItem importmb = new JMenuItem("Import");
        filemb.add(importmb);
        JMenuItem exitmb = new JMenuItem("Exit");
        filemb.add(exitmb);
 
        exitmb.addActionListener(new ActionListener() {
 
            public void actionPerformed(ActionEvent e)
            {
 
                System.exit(0);
 
            }
        }); 
 
        importmb.addActionListener(new ActionListener() {
 
            public void actionPerformed(ActionEvent e)
            {
                try {
                    martin.showOpenDialog(frame1);
                    File selectedFile = martin.getSelectedFile();
 
                    String sexy = selectedFile + "";
                    System.out.println(sexy);
 
                    File file = new File(sexy);
 
                    Scanner martin2 = new Scanner(file);
 
                    int numLines = 0;
                    i = 0;
 
                    while(martin2.hasNext()){
 
                        martin2.nextLine();
                        numLines++;
                        }
 
                    martin2 = new Scanner(file);
 
                    String[] lines = new String[numLines];
                    while(martin2.hasNext()){
 
                        lines[i] = martin2.nextLine();
                        System.out.println(lines[i]);
                        i++;
                    }
                    String active;
                    storeCoordinates = new Double[i*4];
                    int k = i;
                    int q1 = 0;
                    while(k>0){
                        active = lines[i-k];
 
                        int q = 0;
                        String morph = "";
                        while(q<active.length()){
                            if(active.charAt(q) != ','){
                            morph = morph + active.charAt(q);
                            }
                            if(q+1 == active.length() || active.charAt(q) == ','){
 
                                Double dedomraz = Double.valueOf(morph);
                                storeCoordinates[q1] = dedomraz;
                                morph = "";
                                q1++;
                            }
 
                        q++;
 
                        }
 
                        k--;
                    }
 
                    drawing();
 
 
 
 
 
                } catch (FileNotFoundException ex) {
                    Logger.getLogger(LineDrawV2.class.getName()).log(Level.SEVERE, null, ex);
                }
 
            }
        }); 
 
 
        frame1.setVisible(true);
 
 
    }
 
    public static void drawing(){
        DrawingPanel panel = new DrawingPanel();
        frame1.add(panel);
    }
 
}

DrawingPanel

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import javax.swing.JPanel;
import java.lang.Math;
public class DrawingPanel extends JPanel {
    private static final long serialVersionUID = 1L;
 
    public void paintComponent(Graphics g){
        LineDrawV2 LDV2 = new LineDrawV2() {
 
            @Override
            public void actionPerformed(ActionEvent e) {
                throw new UnsupportedOperationException("Not supported yet.");
            }
        };
 
        super.paintComponents(g);
        g.setColor(Color.BLACK);
        g.drawLine(15, 15, 100, 100);
 
 
    }
 
}

so now the problem is that g.drawLine doesn't appear anywhere. I found out if I put drawing(); out of the action listener the line will appear but I need the Line to be drawn after or in the action listener because in the future I will need some numbers from a file that will give the line coordinates (this is just a example line so you can help me just to make it appear...).

Thanks in advance

P.S. It's a messy code but I hope you don't mind...

Problems:

• You shouldn't be creating a new LineDrawV2 object inside of DrawingPanel's paintComponent(...) method. Why do you feel that your program needs this?
• You know that code like this risks a nasty NPE error if you declared DrawingPanel inside of LineDrawV2.
• LineDrawV2 should not be abstract. I believe that you're trying to fix an error the wrong way by making it abstract. The correct solution is to have the class implement all necessary interface methods.
• LineDrawV2 shouldn't extend JFrame or implement any interfaces.
• You shouldn't have any static variables as that only confuses things and makes your program non-OOPs compliant.
• After adding DrawingPanel to the JFrame, the JFrame should be packed.
• You call setVisible(true) on the JFrame *after* adding all components, including LineDraw, not before.
• ... and many more problems.

packing the frame really helped ! Thank You

and one more question

Originally Posted by Fubarable

Problems:

• You know that code like this risks a nasty NPE error if you declared DrawingPanel inside of LineDrawV2.

I'm confused, how can I add the DrawingPanel in the frame if I don't declare it ?

I may have gotten that backwards: you may get an exception, perhaps stackoverflow exception if you define a new LineDrawV2 inside of DrawingPanel's paintComponent. Bottom line is you don't want to create components or add components in the paint or paintComponent method.