no display in JTextArea inspite of using setText function

Question

Here,is something I wanted to show for the use of MouseEvents of one class in another ...by creating an object of the former class...

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.lang.*;
public class MyPagalpanti extends JPanel implements MouseListener
{Point a,b;
boolean drawLin,drawOvl,drawOvl2;
MyPagalpanti(){a=new Point(0,0);b=new Point(0,0);drawLin=false;drawOvl=false,drawOvl2=false;;setSize(300,300);addMouseListener(this);}
public void mouseClicked(MouseEvent m)
{if(!drawOvl){a=new Point(m.getX(),m.getY());drawOvl=true;drawOvl2=false;}
else {b=new Point(m.getX(),m.getY());drawOvl=true;drawOvl2=true;repaint();}//record("clicked",m);}
}
public void mouseEntered(MouseEvent m)
{
}
public void mousePressed(MouseEvent m)
{a=new Point(m.getX(),m.getY());repaint();}
public void mouseReleased(MouseEvent m)
{b=new Point(m.getX(),m.getY());}
public void mouseExited(MouseEvent m)
{}
public void paintComponent(Graphics g)
{if(drawLin){g.setColor(Color.yellow);g.drawLine((int)a.getX(),(int)a.getY(),(int)b.getX(),(int)b.getY());}//d=0;}
else if(drawOvl&&drawOvl2){g.setColor(Color.red);int width=(int)Math.abs(b.getX()-a.getX());
int h=(int)Math.abs(b.getY()-a.getY());
g.drawOval((int)a.getX(),(int)a.getY(),width,h);
}}
}

the class in which an object of MyPagalpanti is formed:

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

public class Mithu extends JFrame// implements MouseListener
{JTextArea jta1,jta2;
Mithu(String title)
{
super(title);
MyPagalpanti p1=new MyPagalpanti();
jta1=new JTextArea();
jta2=new JTextArea();
p1.setOpaque(true);
jta1.setEditable(false);
jta2.setEditable(false);
setForeground(Color.blue);
p1.setPreferredSize(new Dimension(600,600));
p1.setLayout(new GridLayout(3,1,0,0));
getContentPane().add(p1);
pack();
setVisible(true);
}
void record(String s,MouseEvent e)
{jta1.setText(jta1.getText()+"\n"+s+""+e.toString());}
public void mouseClicked(MouseEvent m)
{record("clicked",m);}
public void mouseEntered(MouseEvent m)
{record("entered",m);}
public void mousePressed(MouseEvent m)
{record("pressed",m);}
public void mouseReleased(MouseEvent m)
{ record("released",m);}
public void mouseExited(MouseEvent m)
{record("exited",m);}

public static void main(String args[])
{Mithu m=new Mithu("HI ! Karamvir");
m.setVisible(true);}
}

please don't go word by word...I know my code has many other bugs...coz I am still working on it...but for those who have say that "the MouseEvents will only be delivered to the MouseListener from the component it registered to " ,I guess you are talking correctly but if we see closely, I have used this concept only...in this code..

Answer 1

To add it JBNizet's answer...

MouseListeners will only be delivered to components that are displayable and have registered for notification. Creating a component that is listening for mouse events and adding it you component won't magically make those events delivered to your component.

Then, in top of that, you are adding two components to the default (CENTER) position of a component managed by BorderLayout...

getContentPane().add(panelTop);
//...
getContentPane().add(p1);

This effectively makes the first component invisible, meaning it's not displayable...

• You shouldn't be calling show as it's deprecated, use setVisible instead.
• You should be calling super.paintComponent in your paintComponent method before doing any custom painting, otherwise you'll end up with no end of painting problems
• There is no need for paintComponent to be public as you never want anybody to be able to call it directly...

Updated

Unless you register interest in been notified about events, you will never receive notification, regardless of what objects you create or interfaces you implement.

It's like saying "I'm interested in this movie", but unless you go to the cinemas, you'll never see it...

In order for your Mithu class to receive mouse event notification, it must register a MouseListener against the component that it's interested in monitoring.

The following example registers a a MouseListener in the Mithu class against the instance of MyPagalpanti, which allows it to receive mouse events that are generated by the instance of MyPagalpanti

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestMouseListener {

    public static void main(String[] args) {
        new TestMouseListener();
    }

    public TestMouseListener() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                Mithu m = new Mithu("HI ! Karamvir");
                m.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                m.pack();
                m.setLocationRelativeTo(null);
                m.setVisible(true);
            }
        });
    }

    public class Mithu extends JFrame implements MouseListener
    {

        JTextArea jta1;

        Mithu(String title) {
            super(title);
            MyPagalpanti p1 = new MyPagalpanti();
            p1.addMouseListener(this);
            jta1 = new JTextArea();
            p1.setOpaque(true);
            jta1.setEditable(false);
            setForeground(Color.blue);
            setLayout(new GridLayout(2, 1));
            getContentPane().add(jta1);
            getContentPane().add(p1);
            pack();
            setVisible(true);
        }

        void record(String s, MouseEvent e) {
            jta1.append("\n" + s + "" + e.toString());
        }

        public void mouseClicked(MouseEvent m) {
            record("clicked", m);
        }

        public void mouseEntered(MouseEvent m) {
            record("entered", m);
        }

        public void mousePressed(MouseEvent m) {
            record("pressed", m);
        }

        public void mouseReleased(MouseEvent m) {
            record("released", m);
        }

        public void mouseExited(MouseEvent m) {
            record("exited", m);
        }
    }

    public class MyPagalpanti extends JPanel implements MouseListener {

        Point a, b;
        boolean drawLin, drawOvl, drawOvl2;

        MyPagalpanti() {
            a = new Point(0, 0);
            b = new Point(0, 0);
            drawLin = false;
            drawOvl = false;
            drawOvl2 = false;
            setSize(300, 300);
            addMouseListener(this);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        public void mouseClicked(MouseEvent m) {
            if (!drawOvl) {
                a = new Point(m.getX(), m.getY());
                drawOvl = true;
                drawOvl2 = false;
            } else {
                b = new Point(m.getX(), m.getY());
                drawOvl = true;
                drawOvl2 = true;
                repaint();
            }//record("clicked",m);}
        }

        public void mouseEntered(MouseEvent m) {
        }

        public void mousePressed(MouseEvent m) {
            a = new Point(m.getX(), m.getY());
            repaint();
        }

        public void mouseReleased(MouseEvent m) {
            b = new Point(m.getX(), m.getY());
        }

        public void mouseExited(MouseEvent m) {
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.RED);
            FontMetrics fm = g.getFontMetrics();
            if (a != null && b != null) {
                g.drawString(a + "-" + b, 0, fm.getHeight());
            }
            if (drawLin) {
                g.setColor(Color.yellow);
                g.drawLine((int) a.getX(), (int) a.getY(), (int) b.getX(), (int) b.getY());
            }//d=0;}
            else if (drawOvl && drawOvl2) {
                g.setColor(Color.red);
                int width = (int) Math.abs(b.getX() - a.getX());
                int h = (int) Math.abs(b.getY() - a.getY());
                g.drawOval((int) a.getX(), (int) a.getY(), width, h);
            }
        }
    }

}

Before you go to much further, you really should read through...

• Performing Custom Painting
• Painting in AWT and Swing

As you are going to have some very nasty suprises if you keep following your current approach.

Also, it wouldn't hurt to read through How to Write a Mouse Listener

Answer 2

Your class has mouseClicked(), mouseReleased() etc. methods, but it doesn't implement MouseListener. And even if it was, it's never added as a MouseListener to any component.

So, make your class implement MouseListener:

public class MouseEvtEx2 extends JFrame implements MouseListener {

and add itself as mouse listener to the component you want to listen to:

panelTop.addMouseListener(this);

And of course, to help yourself read and understand your own code, indent it properly.

Answer 3

I made couple of changes to make it work. you need to implement MouseListener on your MouseEvtEx2 Frame and also you need to add it as the MouseListener to your panel p1

public class MouseEvtEx2 extends JFrame implements MouseListener {
    private JTextArea txtArea;

    public MouseEvtEx2(String title) {
        super(title);
        Panel p1 = new Panel();
        MyPanel panelTop = new MyPanel();
        panelTop.setBackground(new Color(0.98f, 0.97f, 0.85f));
        panelTop.setOpaque(true);
        panelTop.setPreferredSize(new Dimension(400, 200));
        panelTop.setBorder(BorderFactory.createRaisedBevelBorder());

        getContentPane().add(panelTop);
        txtArea = new JTextArea();
        txtArea.setEditable(false);
        JScrollPane pane = new JScrollPane(txtArea);
        pane.setPreferredSize(new Dimension(400, 200));
        p1.setLayout(new GridLayout(2, 1, 0, 0));
        getContentPane().add(p1);
        p1.addMouseListener(this);
        p1.add(pane);

        // txtArea.setText
        // revalidate();
        setSize(600, 600);
        show();
    }

    public void record(String st, MouseEvent et) {
        txtArea.setText("" + st + "" + et.toString());
    }// setVisible(true);}

    public void mouseClicked(MouseEvent evt) {
        record("Mouse clicked # of mouse clicks: " + evt.getClickCount(), evt);// +
                                                                                // " "
                                                                                // +

    }

    public void mouseEntered(MouseEvent evt) {
        record("Mouse entered ", evt);// .toString());
    }

    public void mouseExited(MouseEvent evt) {
        record("Mouse exited ", evt);// .toString());
    }

    public void mousePressed(MouseEvent evt) {
        record("Mouse pressed # of mouse clicks: ", evt);// .getClickCount() +
                                                            // " " +

    }

    public void mouseReleased(MouseEvent evt) {
        record("Mouse released ", evt);
    }

    public static void main(String[] args) {
        new MouseEvtEx2("Mouse events");
    }
}

Hope this helps.