Serializable problem

Programming Questions

el_dippo

in Programming Questions • 8 months ago

Hello all,

I am trying to make a (java) program that communicates with an other (java) program. After some searching i found out that doing it serializable, would be the easiest way because i don't have to worry about the format. So i found this example in my book Head First: Java. Except, the code below does work, but gives an error after a while ("NotSerializableException"). If i look at the output then it seems to include the Processing constants also, i didn't expect this.

Is there a way to get this working? Thanks.

p.s. made with Processing 1.5.1.

import java.io.*;
void setup() {
GameChar Elf = new GameChar(50, "ranged", "bow");
try {
ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream(sketchPath+"/data/game.txt"));
os.writeObject(Elf);
os.close();
}
catch (Exception e) {
println(e);
}
exit();
}
void draw() {
}
class GameChar implements Serializable {
int health;
String type;
String weapon;
GameChar(int h, String t, String w) {
health = h;
type = t;
weapon = w;
}
}

Replies(7)

quarks

Re: Serializable problem

8 months ago

Since GameChar is an inner class it has a reference to the PApplet child class so when you attempt to save the inner class object it is attempting to serialise the PApplet class and that is not serialisable.

The solution is to promote the GameChar class from an inner class to a top-level class and you can do this in two ways.

Change line 16 to static class GameChar implements Serializable {
or create a new tab in Processing call it GameChar.java and move the class code (lines 16 - 25) into this new tab

el_dippo

Re: Serializable problem

8 months ago

Thank you, you mighty one!

GoToLoop

Re: Serializable problem

8 months ago

I've liked this Serializable thing a lot. May be useful sometimes!
Gonna save in my /examples folder!

/**
 * Serializable (1.2)
 * by el_dippo (2013/Feb)
 *
 * http://forum.processing.org/topic/serializable-problem
 */

//import java.io.*;

void setup() {
  GameChar Elf  = new GameChar(50, "ranged", "bow");
  GameChar Ogre = new GameChar(80, "melee", "axe");

  println(Elf);
  println(Ogre);

  try {
    ObjectOutputStream os = new ObjectOutputStream( 
    new FileOutputStream(sketchPath + "/data/game.txt") );

    os.writeObject(Elf);
    os.writeObject(Ogre);

    os.close();
  }
  catch (Exception e) {
    println(e);
  }

  exit();
}

final static class GameChar implements Serializable {
  int health;
  String type, weapon;

  GameChar(int h, String t, String w) {
    health = h;
    type = t;
    weapon = w;
  }

  @Override String toString() {
    return "Health: " + health + "\t\t Type: " + type 
      + "\t Weapon: " + weapon;
  }
}

quarks

Re: Serializable problem

8 months ago

@GoToLoop you do not need to make the inner class final for it to be serializable. When final is applied to a class it prevents the class being extended (inhertited from)

The main advantage of serializable is that all the Java collection classes e.g. ArrayList, HashMap etc. are serializable, so if they can contain serializable objects then the whole collection can be saved off in one go.

There are some disadvantages as well but they can be overcome.

GoToLoop

Re: Serializable problem

8 months ago

I know that final makes a class not extendable and a method not overridable.
It's just for a possible optimization chance! ;-)

el_dippo

Re: Serializable problem

8 months ago

Always good to make somebody happy!
This is the full example code:

import java.io.*;
GameChar Elf, Troll;
void setup() {
Elf = new GameChar(50, new String[] {
"bow", "sword", "dust"
}
);
Troll = new GameChar(200, new String[] {
"bare hands", "big axe"
}
);
try {
ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream(sketchPath+"/data/game.txt"));
os.writeObject(Elf);
os.writeObject(Troll);
os.close();
}
catch (Exception e) {
println(e);
}
Elf = null;
Troll = null;
try {
ObjectInputStream is = new ObjectInputStream(new FileInputStream(sketchPath+"/data/game.txt"));
Elf = (GameChar) is.readObject();
Troll = (GameChar) is.readObject();
println("Elf has "+ Elf.getHealth()+" health, and fights with "+ Elf.getWeapons());
println("Troll has "+ Troll.getHealth()+" health, and fights with "+ Troll.getWeapons());
}
catch (Exception e) {
println(e);
}
}
void draw() {
}
static class GameChar implements Serializable {
int health;
String[] weapons;
GameChar(int h, String[] w) {
health = h;
weapons = w;
}
int getHealth() {
return health;
}
String getWeapons() {
String weaponList = "";
for (String weapon : weapons)
weaponList += weapon + " ";
return weaponList;
}
}

quarks

Re: Serializable problem

8 months ago

Serialization makes the saving and loading of complex objects quite easy but there are 2 restrictions you should be aware of.

If a class is serializable then the attributes must also be serializable. For instance PImage is not serializable so if your class had a PImage attribute then the class is not serializable. There are solutions to this but they involve extra code.
If you have some objects that you have serialized, then change the class code it is most likely that you will not be able to deserialize the object.

As long as you are aware of these constraints serialzation is a very powerful tool.

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