Question

I am trying to implement a menu based graph – wherein i will represent a vertex by a circle and each circle will have an index provided by the user.The user has to go to File menu and click on Addvertex to create a new node with an index.The Problem though is – The circle is drawn only once – any subsequent clicks to addVertex does not result in drawing of a circle -Can’t understand Why…

Here is my code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.io.*;
import java.util.*;

public class FileChoose extends JFrame {

    public FileChoose() {
        JMenuBar l=new JMenuBar();
        JMenu file=new JMenu("File");
        JMenuItem open=new JMenuItem("Addvertex");
        open.addActionListener(new Drawer());
        JMenuItem close=new JMenuItem("Exit");
        close.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {
                System.exit(0);
            }
        });
        JMenu tools=new JMenu("Tools");
        file.add(open);
        file.add(close);

        this.setJMenuBar(l);
        l.add(tools);
        l.add(file);

        this.setSize(new Dimension(200, 200));
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
    }

    void HelloHere(String p) {
        Draw d = new Draw(p);
        this.add(d);
        setExtendedState(MAXIMIZED_BOTH);
    }

    class Drawer extends JFrame implements ActionListener {

        Integer index;

        public void actionPerformed(ActionEvent e) {
            JPanel pn = new JPanel();
            JTextField jt = new JTextField(5);
            JTextField jt1 = new JTextField(5);
            pn.add(jt);
            pn.add(jt1);
            int result=JOptionPane.showConfirmDialog(null, pn, "Enter the values", JOptionPane.OK_CANCEL_OPTION);
            if (result == JOptionPane.OK_OPTION) {
                index = Integer.parseInt(jt.getText());
                System.out.println(jt1.getText());
            }

            this.setVisible(true);
            this.setSize(500, 500);
            this.setLocationRelativeTo(null);

            HelloHere(index.toString());
        }
    }

    public static void main(String [] args) {
        FileChoose f = new FileChoose();
        f.setVisible(true);
    }
}

class Draw extends JPanel {

    String inp;

    public Draw(String gn) {
        inp = gn;
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D) g;
        Random r = new Random();
        int x = r.nextInt(100);

        g2.drawOval(x, x * 2, 100, 100);
        g2.drawString(inp, x + (x / 2), x + (x / 2));
    }
}

Answer 1

Some pointers:

• Use EDT for creation and manipulation of Swing Components.

• Dont extend JFrame class unnecessarily.

• Use anonymous Listeners where possible/allowed

• Make sure JFrame#setVisible(..) is the last call on JFrame instance specifically pointing here:

      this.setVisible(true);
      this.setSize(500, 500);
      this.setLocationRelativeTo(null);
      HelloHere(index.toString());
  

• Call pack() on JFrame instance rather than setSize(..)

• Do not use multiple JFrames see: The Use of Multiple JFrames: Good or Bad Practice?

• The problem you are having is here:

  Draw d = new Draw(p);
  this.add(d);
  

  You are creating a new instance of Draw JPanel each time and then overwriting the last JPanel added with the new one (this is default the behavior of BorderLayout). To solve this read below 2 points:

• Call revalidate() and repaint() on instance after adding components to show newly added components.

• Use an appropriate LayoutManager

As I am not sure of you expected results I have done as much fixing of the code as I could hope it helps:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.*;
import javax.swing.*;

public class FileChoose {

    JFrame frame;

    public FileChoose() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JMenuBar l = new JMenuBar();
        JMenu file = new JMenu("File");
        JMenuItem open = new JMenuItem("Addvertex");

        open.addActionListener(new ActionListener() {
            Integer index;

            @Override
            public void actionPerformed(ActionEvent e) {
                JPanel pn = new JPanel();
                JTextField jt = new JTextField(5);
                JTextField jt1 = new JTextField(5);
                pn.add(jt);
                pn.add(jt1);
                int result = JOptionPane.showConfirmDialog(null, pn, "Enter the values", JOptionPane.OK_CANCEL_OPTION);
                if (result == JOptionPane.OK_OPTION) {
                    index = Integer.parseInt(jt.getText());
                    System.out.println(jt1.getText());
                }
                HelloHere(index.toString());
            }
        });

        JMenuItem close = new JMenuItem("Exit");
        close.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.exit(0);
            }
        });

        JMenu tools = new JMenu("Tools");
        file.add(open);
        file.add(close);

        frame.setJMenuBar(l);
        l.add(tools);
        l.add(file);
        frame.pack();

        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    void HelloHere(String p) {
        Draw d = new Draw(p);
        frame.add(d);
        frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
        frame.revalidate();
        frame.repaint();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                FileChoose f = new FileChoose();
            }
        });
    }
}

class Draw extends JPanel {

    String inp;

    public Draw(String gn) {
        inp = gn;
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D) g;
        Random r = new Random();
        int x = r.nextInt(100);

        g2.drawOval(x, x * 2, 100, 100);
        g2.drawString(inp, x + (x / 2), x + (x / 2));
    }
}

UPDATE:

Declare this globally in your Draw class: Random r=new Random(); as if you iniate a new Random instance each time you call paintComponent() the distributions will not be significant/random enough