Part 3
Interview questions on serialization in java for experienced covered in this post:
How will you prevent to be serialized child class when its parent class is Serializable?
-
There is no direct way to prevent child class from
serialization. You can override writeObject() and readObject() methods in
your child class and then explicitly throw NotSerializableException. It will
prevent child class from serialization.
-
Please refer to the below example.
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package simplifiedjava.crackedInterview; import java.io.Serializable; public class Parent implements Serializable{ public int i;
public
Parent() {
System.out.println("Parent Class no-arg constructor called."); }
public
Parent(int
i) {
this.i
= i; }
public
void
check(){
System.out.println("Parent Class check() method");
}
} package simplifiedjava.crackedInterview;
import
java.io.NotSerializableException;
import
java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class Child extends Parent{
int
j;
public Child() {
}
public
Child(int
i,int
j) {
super(i);
this.j
= j; }
public
void
check(){
System.out.println("Addition in Child Class "+ (i
+ j));
}
private
void
writeObject(ObjectOutputStream oos)throws
NotSerializableException {
throw
new
NotSerializableException(); }
private
void
readObject(ObjectInputStream ois) throws
NotSerializableException {
throw
new
NotSerializableException();
}
} package simplifiedjava.crackedInterview;
import
java.io.File;
import
java.io.FileInputStream;
import
java.io.FileOutputStream;
import
java.io.IOException;
import
java.io.ObjectInputStream; import java.io.ObjectOutputStream;
public
class
SerializationInHeritanceDemo { public static void main(String[] args) throws IOException, ClassNotFoundException {
Child c1
= new
Child(10,20); System.out.println("Values Before Serialization : " + c1.i +" and "+ c1.j);
FileOutputStream fos
= new
FileOutputStream(new
File("abc.ser"));
ObjectOutputStream oos
= new
ObjectOutputStream(fos); oos.writeObject(c1);
FileInputStream fis
= new
FileInputStream("abc.ser");
ObjectInputStream ois
= new
ObjectInputStream(fis);
Child c2
=(Child) ois.readObject();
System.out.println("Values After Deserialization : "+ c2.i
+" and "+ c2.j); }
Values Before Serialization : 10 and 20
Exception in thread "main" java.io.NotSerializableException
at simplifiedjava.crackedInterview.Child.writeObject(Child.java:26)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown
Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown
Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeWriteObject(Unknown
Source)
at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown
Source)
at java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.io.ObjectOutputStream.writeObject(Unknown Source)
at
simplifiedjava.crackedInterview.SerializationInHeritanceDemo.main(SerializationInHeritanceDemo.java:19)
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What is NotSerializableException? When it can be thrown?
-
The NotSerializableException is thrown when attempting to
serialize or deserialize an object that does not implement the java.
io.Serializable interface.
-
Please refer to the below example.
|
package simplifiedjava.crackedInterview; import java.io.Serializable; public class Parent{ public int i;
public
Parent() {
System.out.println("Parent Class no-arg constructor called."); }
public
Parent(int
i) {
this.i
= i; }
public
void
check(){
System.out.println("Parent Class check() method");
}
} package simplifiedjava.crackedInterview;
import
java.io.NotSerializableException;
import
java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class Child extends Parent{ int j; public Child() {
}
public
Child(int
i,int
j) {
super(i);
this.j
= j; }
public
void
check(){
System.out.println("Addition in Child Class "+ (i
+ j));
}
} package simplifiedjava.crackedInterview;
import
java.io.File;
import
java.io.FileInputStream;
import
java.io.FileOutputStream;
import
java.io.IOException;
import
java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class SerializationInHeritanceDemo { public static void main(String[] args) throws IOException, ClassNotFoundException {
Child c1
= new
Child(10,20); System.out.println("Values Before Serialization : " + c1.i +" and "+ c1.j);
FileOutputStream fos
= new
FileOutputStream(new
File("abc.ser"));
ObjectOutputStream oos
= new
ObjectOutputStream(fos); oos.writeObject(c1);
FileInputStream fis
= new
FileInputStream("abc.ser");
ObjectInputStream ois
= new
ObjectInputStream(fis);
Child c2
=(Child) ois.readObject();
System.out.println("Values After Deserialization : "+ c2.i
+" and "+ c2.j); }
Output:
Values Before Serialization : 10 and 20
Exception in thread "main" java.io.NotSerializableException: simplifiedjava.crackedInterview.Child
at java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.io.ObjectOutputStream.writeObject(Unknown Source)
at
simplifiedjava.crackedInterview.SerializationInHeritanceDemo.main(SerializationInHeritanceDemo.java:19) |
 
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What are the scenarios where InvalidClassException can be thrown?
-
InvalidClassException can be thrown in following scenarios.
1.
The serial version of the class does not match that of the
class descriptor read from the stream.
2.
The class contains unknown data types.
3.
The parent class does not have an accessible no-arg
constructor while performing deserialization.
At the time of deserialization why do we must require default constructor in parent class if parent class is not Serializable?
-
At the time of de-serialization, if any non-serializable
superclass is present then JVM will execute instance control flow in the
superclass. To execute instance control flow in a class, JVM will always
invoke the constructor of that class. So every non-serializable superclass
must necessarily contain a default constructor, otherwise, we will get
InvalidClassException.
-
Please refer to the below example.
|
package simplifiedjava.crackedInterview; import java.io.Serializable; public class Parent{ public int i;
public
Parent(int
i) {
this.i
= i; }
public
void
check(){
System.out.println("Parent Class check() method");
}
} package simplifiedjava.crackedInterview;
import
java.io.NotSerializableException;
import
java.io.ObjectInputStream;
import
java.io.ObjectOutputStream; import java.io.Serializable; public class Child extends Parent implements Serializable{ int j;
public
Child(int
i,int
j) {
super(i);
this.j
= j; }
public
void
check(){
System.out.println("Addition in Child Class "+ (i
+ j));
}
} package simplifiedjava.crackedInterview;
import
java.io.File;
import
java.io.FileInputStream;
import
java.io.FileOutputStream;
import
java.io.IOException;
import
java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class SerializationInHeritanceDemo { public static void main(String[] args) throws IOException, ClassNotFoundException {
Child c1
= new
Child(10,20); System.out.println("Values Before Serialization : " + c1.i +" and "+ c1.j);
FileOutputStream fos
= new
FileOutputStream(new
File("abc.ser"));
ObjectOutputStream oos
= new
ObjectOutputStream(fos); oos.writeObject(c1);
FileInputStream fis
= new
FileInputStream("abc.ser");
ObjectInputStream ois
= new
ObjectInputStream(fis);
Child c2
=(Child) ois.readObject();
System.out.println("Values After Deserialization : "+ c2.i
+" and "+ c2.j);
}
} |
Can we customize serialization process? Can you override default serialization process if yes then how. Can you tell me the steps?
- Yes, We can customize the Serialization.
- We can use Externalization to customize the
serialization.
- Steps needs to implement for Externalization.
1. A class must implement an Externalizable interface.
2. We have to override writeExternal(ObjectOutputStream ooo) and
readExternal(ObjectOutputStream oos).
3. Inside the main method, we have to create a file object to
store the serialised data.
4. Create FileOutputStream object to write the file. We have to
pass the file object in the FileOutputStream class constructor.
5. Create ObjectOutputStream object to and pass fileOutputstream
object to its constructor.
6. With the ObjectOutputStream object, you can write the data.
- Java interview questions and answers all MNC - Click here
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- Core java interview questions for 3 years experience - Click here
- Core java interview questions and answers for 3-5 years exp - Click here
- Core java interview questions and Answers for 5 - 7 Years exp - Click here
- Basic Java Interview Questions and Answers - Click here
- Java interview questions and answers on oops - Click here
- Java interview questions and answers on Strings - Click here
- Java interview questions on exception handling - Click here
- Interview questions on multithreading in java for experienced - Click here
- Interview questions on serialization in java for experienced - Click here
- Interview questions on inner class in java for experienced - Click here
- Interview questions on Collections in java for experienced - Click here
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
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