How do I control whether a class is declared serializable or not?

[DrMadolite]

Hi!

I'm a newcomer to java and there's this problem that I seem to have with Eclipse that none of the tutorial people on youtube seem to have. As I create a new class, there's sometimes (but not always) this thing that happens that gives me an yellow error unless I add the method "private static final long serializedVersionUID = 1L;" to it.

I've looked around on the internet and I've learned that this should only pop up for a class that has been declared serializable. But I don't get what I could've done to declare it serializable? Is it something I did in the code or some option I overlooked in Eclipse as I created the class?

In other words, how do I un-serialize a class within java?

Thanks!

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JPanel;
import javax.swing.Timer;


public class HeroFrame extends JPanel implements ActionListener {

/**
*
*/
private static final long serialVersionUID = 1L;


Timer mainTimer;
Player player;

int enemyCount = 5;

static ArrayList<Enemy> enemies = new ArrayList<Enemy>();
Random rand = new Random();

public HeroFrame() {
setFocusable(true);

player = new Player (100, 100);
addKeyListener(new KeyAdapt(player));

mainTimer = new Timer(20, this);
mainTimer.start();

for (int i = 0; i < enemyCount; i++) {
addEnemy(new Enemy(rand.nextInt(800), rand.nextInt(600)));

}

}

public void paint (Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;

player.draw(g2d);

for (int i = 0; i < enemies.size(); i++) {
Enemy tempEnemy = enemies.get(i);
tempEnemy.draw(g2d);

}

}

@Override
public void actionPerformed(ActionEvent arg0) {
player.update();
repaint();
}

public void addEnemy(Enemy e) {
enemies.add(e);

}

public static void removeEnemy(Enemy e) {
enemies.remove(e);

}

public static ArrayList<Enemy> getEnemyList() {
return enemies;

}

}

[doWhile]

Serializable is an interface
Serializable Objects (The Java™ Tutorials > Java Naming and Directory Interface > Java Objects in the Directory)
Component implements Serializable, JPanel extends Component, and your class extends JPanel. Thus, by inheritance, your class implements Serializable.
http://docs.oracle.com/javase/6/docs...ng/JPanel.html

The yellow icon is not an error, it is a warning. If you wish to suppress the warning, add the following...

@SuppressWarnings("serial")

...above the class definition. That being said, why not just add the serialVersionUID variable?

[DrMadolite]

That being said, why not just add the serialVersionUID variable?

Thanks for the answer. The reason why I feel reluctant about adding the serialVersionUID variable is just because I was unsure what it did and I read something here:

Java Practices -> Implementing Serializable

"Do not implement Serializable lightly, since it restricts future flexibility, and publicly exposes class implementation details which are usually private."

I think I'll just ignore the warning for now and maybe add that annotation. Thanks again.

[JosAH]

Eclipse can add the serialVersionUID for you: right click on the warning icon and select 'Quick Fix'; select 'Add generated serial verion UID' and voila.

kind regards,

Jos