Serialization is not for static variables - Really true?

[Steffen Hauser]

Hi,

extract from the K&B book(chapter 6, page 456):

Static variables are NEVER saved as part of the object's state…because they do not belong to the object!

So why is the output of the following code "55" and not "21"?

public class SerTest implements Serializable {
	private static int i= 21;
	
	public static void main(String[] args) throws Exception {
		SerTest stOut = new SerTest();
		stOut.i = 55;
		
		FileOutputStream fos = new FileOutputStream("st.ser");
		ObjectOutputStream oos = new ObjectOutputStream(fos);
		oos.writeObject(stOut);
		
		FileInputStream fis = new FileInputStream("st.ser");
		ObjectInputStream ois = new ObjectInputStream(fis);
		SerTest stIn = (SerTest) ois.readObject();
		System.out.println(stIn.i);
	}
}

Regards,
-Steffen-

[Henry Wong]

So why is the output of the following code "55" and not "21"?

Maybe this slight modification to your code can explain it...

public class SerTest implements Serializable {   
    private static int i= 21;   
       
    public static void main(String[] args) throws Exception {   
        SerTest stOut = new SerTest();   
        stOut.i = 55;   
           
        // FileOutputStream fos = new FileOutputStream("st.ser");   
        // ObjectOutputStream oos = new ObjectOutputStream(fos);   
        // oos.writeObject(stOut);   
           
        // FileInputStream fis = new FileInputStream("st.ser");   
        // ObjectInputStream ois = new ObjectInputStream(fis);   
        // SerTest stIn = (SerTest) ois.readObject();
        SerTest stIn = new SerTest();   
        System.out.println(stIn.i);   
    }   
}  

Henry

[Jesper de Jong]

Static variables are class-level variables; there is only one copy of the variable which is shared by all instances of that class.

In line 6, you set i to 55, but remember that there is only one copy of i shared by all instances of class SerTest. So i will be 55 also for the new SerTest object that you read in from the serialized file in line 14 - that's to be expected, and does not demonstrate that the static variable is serialized.

[binayakumar patel]

Class Variables
When a number of objects are created from the same class blueprint, they each have their own distinct copies of instance variables. In the case of the Bicycle class, the instance variables are cadence, gear, and speed. Each Bicycle object has its own values for these variables, stored in different memory locations.
Sometimes, you want to have variables that are common to all objects. This is accomplished with the static modifier. Fields that have the static modifier in their declaration are called static fields or class variables.

Thats why the value get change....

[Lucas Smith]

OK, that's right.
So the static variables get their default values or the values they were initialized by?

[Henry Wong]

Lukas Smith wrote:OK, that's right.
So the static variables get their default values or the values they were initialized by?

Static variables are initialized when the classes are loaded. They are not affected, when an instance of the class is created.

Henry