Question

I am trying to learn more about java. This program is an attempt to understand events as well as serialization. What i am attempting to do is flatten an object when the user closes the JFrame and re-inflate it when the program is started. I know i can create the serialized file but having it take effect again isn’t working. Any help in the right direction would be wonderful. Thank you in advance.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.Timer;
import java.io.*;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class tempusFugit extends JFrame implements ActionListener, Serializable, WindowListener
{
String fileN = "tf.txt"; 
public int ToL = 0;
String outT = Integer.toString(ToL);
    JLabel jl = new JLabel(outT);

FileOutputStream fos = null;
ObjectOutputStream out = null;

public tempusFugit()

{
    Timer timer = new Timer(1000, this);

    setBounds(250, 250, 250, 190);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLayout(new FlowLayout(FlowLayout.LEFT) );
    setVisible(true);
    add(jl);
    timer.start();
}

public void actionPerformed(ActionEvent e)
{
    ++ToL;
    outT = Integer.toString(ToL);
    jl.setText(outT);
    validate();
    repaint();
}
public static void main(String[] args)
{
    tempusFugit tf = new tempusFugit();
    tf.addWindowListener( tf );

}
public void windowDeactivated(WindowEvent e)
{
}
public void windowActivated(WindowEvent e)
{   
}
public void windowDeiconified(WindowEvent e)
{
}
public void windowIconified(WindowEvent e)
{
}
public void windowClosed(WindowEvent e)
{
}
public void windowClosing(WindowEvent e)
{
    try
    {
        fos = new FileOutputStream(fileN);
        out = new ObjectOutputStream(fos);
        out.writeObject(this);
        out.close();

    }
    catch(IOException ex)
    {
}
}
public void windowOpened(WindowEvent e)
{
try
    {
        tempusFugit tf = new tempusFugit();
        FileInputStream fis = new FileInputStream(fileN);
        ObjectInputStream in = new ObjectInputStream(fis);
        tf = (tempusFugit)in.readObject();
        this.ToL = tf.ToL;
    }
    catch(IOException ex)
    {
    }
    catch(ClassNotFoundException ce)
    {
    }

}

}

I assume i’m trying to recreate the object at the wrong time. Even though the object is serialized correctly i can not access it again with the windowOpened function. Do i need to try to use

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException;

somehow?

What i end up with is an error saying i am trying to access a Final object (i assume my this). I find that very odd that i cant repopulate my current ‘this’ with another similar object.

Am i way off base?

Again thank you for your time.

Answer 1

Note that there are much simpler ways to do this than serializing the frame, and much better things to serialize than the frame itself.

See What is the best practice for setting JFrame locations in Java? for an example of storing the location and size of a frame. It would be trivial to adapt that to store the count.

---

But here is an attempt based on your code.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.Timer;
import java.io.*;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class tempusFugit extends JFrame implements ActionListener, Serializable, WindowListener
{
    String fileN = "tf.txt";
    public int ToL = 0;
    JLabel jl = new JLabel("" + ToL);

    public tempusFugit()
    {
        Timer timer = new Timer(1000, this);

        setBounds(250, 250, 250, 190);
        setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT) );
        setVisible(true);
        add(jl);
        timer.start();
    }

    public void actionPerformed(ActionEvent e)
    {
        ++ToL;
        jl.setText("" + ToL);
        validate();
        repaint();
    }

    public static void main(String[] args)
    {
        tempusFugit tf = new tempusFugit();
        tf.addWindowListener( tf );
    }

    public void windowDeactivated(WindowEvent e){}
    public void windowActivated(WindowEvent e){}
    public void windowDeiconified(WindowEvent e){}
    public void windowIconified(WindowEvent e){}
    public void windowClosed(WindowEvent e){}

    public void windowClosing(WindowEvent e)
    {
        try
        {
            FileOutputStream fos = new FileOutputStream(fileN);
            ObjectOutputStream out = new ObjectOutputStream(fos);
            out.writeObject(this);
            out.flush();
            out.close();
            setVisible(false);
            System.exit(0);
        }
        catch(IOException ex)
        {
            JOptionPane.showMessageDialog(null, ex);
            System.exit(1);
        }
    }

    public void windowOpened(WindowEvent e)
    {
        try
        {
            tempusFugit tf;// = new tempusFugit();
            FileInputStream fis = new FileInputStream(fileN);
            ObjectInputStream in = new ObjectInputStream(fis);
            tf = (tempusFugit)in.readObject();
            this.ToL = tf.ToL;
            //tf.setVisible(false);
        }
        catch(IOException ex)
        {
            ex.printStackTrace();
        }
        catch(ClassNotFoundException ce)
        {
            ce.printStackTrace();
        }
    }
}