Only subclass has implemented Serializable
interface.
import java.io.*; public class NewClass1{ private int i; NewClass1(){ i=10; } int getVal() { return i; } void setVal(int i) { this.i=i; } } class MyClass extends NewClass1 implements Serializable{ private String s; private NewClass1 n; MyClass(String s) { this.s = s; setVal(20); } public String toString() { return s + " " + getVal(); } public static void main(String args[]) { MyClass m = new MyClass("Serial"); try { ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("serial.txt")); oos.writeObject(m); //writing current state oos.flush(); oos.close(); System.out.print(m); // display current state object value } catch (IOException e) { System.out.print(e); } try { ObjectInputStream ois = new ObjectInputStream(new FileInputStream("serial.txt")); MyClass o = (MyClass) ois.readObject(); // reading saved object ois.close(); System.out.print(o); // display saved object state } catch (Exception e) { System.out.print(e); } } }
One thing, which I noticed here is, parent class is not serialized. Then, why didn't it throw NotSerializableException
indeed it is showing following
Output
Serial 20 Serial 10
Also, output differ from Serialization
and De-serialization
. I just only know, it is because of parent class has not implemented Serializable
. But, If anyone explain me, what happens during object serialization and de-serialization. How it changes the value ? I'm not able to figure out, also I have used comment in my program. So, if I'm wrong at any point, please let me know.
Hence, even though subclass doesn't implement Serializable interface( and if its superclass implements Serializable), then we can serialize subclass object.
No. If you want to serialise an object it must implement the tagging Serializable interface.
It'll throw a NotSerializableException when you try to Serialize it. To avoid that, make that field a transient field.
In order to prevent subclass from serialization we need to implement writeObject() and readObject() methods which are executed by JVM during serialization and deserialization also NotSerializableException is made to be thrown from these methods.
according to the Serializable javadoc
During deserialization, the fields of non-serializable classes will be initialized using the public or protected no-arg constructor of the class. A no-arg constructor must be accessible to the subclass that is serializable. The fields of serializable subclasses will be restored from the stream.
also, serialization exception is only thrown if the class being serialized is not serializable. having non-serializable parents is fine (as long as they have a no-arg constructor). Object itself isnt Serializable, and everything extends it. the quote above also explains why you get different values for the value field - the no-arg constructor for the parent class is set, which sets the value field to 10 - the field belongs to the (non-serializable) parent so its value isnt written to/read from the stream.
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