Prove this: "Serialization Is Not for Statics" in java?

Consider this simple example:

// Animal.java

import java.io.*;

public class Animal implements Serializable

{

public static int numberOfAnimals;

public String name;

public String type;

public int age;

public Animal(String name, String type, int age)

{

this.name = name;

this.type = type;

this.age = age;

numberOfAnimals++;

}

public String toString()

{

return "Name = " + name + ", Type = " + type + ", Age = " +

age;

}

public static void main(String[] args)

{

String filename = "animal.ser";

Animal a = new Animal("Leo", "Lion", 3);

System.out.println("Number of animals before serialization is " + Animal.numberOfAnimals);

// serialize the object to file

FileOutputStream fos = null;

ObjectOutputStream out = null;

try

{

fos = new FileOutputStream(filename);

out = new ObjectOutputStream(fos);

out.writeObject(a);

out.close();

}

catch (Exception ex)

{

ex.printStackTrace();

}

// now change the static field

Animal.numberOfAnimals = 5;

// deserialize the object from file

FileInputStream fis = null;

ObjectInputStream in = null;

try

{

fis = new FileInputStream(filename);

in = new ObjectInputStream(fis);

a = (Animal)in.readObject();

in.close();

}

catch (Exception ex)

{

ex.printStackTrace();

}

System.out.println(a);

System.out.println("Number of animals after deserialization is " + Animal.numberOfAnimals);

}

When you compile and run this program the output is:

Number of animals before serialization is 1

Name = Leo, Type = Lion, Age = 3

Number of animals after deserialization is 5

The value of the static field, numberOfAnimals, has changed from 1 to 5 because we set it to 5 after we'd serialized the object.

As the original value of 1 has not been restored, this proves that static fields are not serialized.

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes12y ago
Accepted answer
Consider this simple example:

// Animal.java

import java.io.*;

public class Animal implements Serializable
{
public static int numberOfAnimals;
public String name;
public String type;
public int age;

public Animal(String name, String type, int age)
{
this.name = name;
this.type = type;
this.age = age;
numberOfAnimals++;
}

public String toString()
{
return "Name = " + name + ", Type = " + type + ", Age = " +

age;
}

public static void main(String[] args)
{
String filename = "animal.ser";
Animal a = new Animal("Leo", "Lion", 3);
System.out.println("Number of animals before serialization is " + Animal.numberOfAnimals);

// serialize the object to file
FileOutputStream fos = null;
ObjectOutputStream out = null;
try
{
fos = new FileOutputStream(filename);
out = new ObjectOutputStream(fos);
out.writeObject(a);
out.close();
}
catch (Exception ex)
{
ex.printStackTrace();
}

// now change the static field
Animal.numberOfAnimals = 5;

// deserialize the object from file

FileInputStream fis = null;
ObjectInputStream in = null;
try
{
fis = new FileInputStream(filename);
in = new ObjectInputStream(fis);
a = (Animal)in.readObject();
in.close();
}
catch (Exception ex)
{
ex.printStackTrace();
}

System.out.println(a);
System.out.println("Number of animals after deserialization is " + Animal.numberOfAnimals);
}
}

When you compile and run this program the output is:

Number of animals before serialization is 1
Name = Leo, Type = Lion, Age = 3
Number of animals after deserialization is 5

The value of the static field, numberOfAnimals, has changed from 1 to 5 because we set it to 5 after we'd serialized the object.

As the original value of 1 has not been restored, this proves that static fields are not serialized.

0
Abhijeet Singh12y ago
Thank you sir.. :)
0