Part 1
Interview questions on serialization in java for experienced covered in this post:
Can
you tell me what are the Serializable and Externalizable?
- Serializable and Externalizable are the Interfaces.
- Serializable interface Externalizable interface belongs to
java.io. package.
What
are the advantages and disadvantages of Serialization?
- Advantages of Serialization.
1. Convert the object onto the byte stream and transfer it
through the network.
2. A converted byte stream can save into a file or
database.
3. Third-party services do not require implementing
serialization.
4. Serialization allows java to perform Encryption,
decryption, Authentication etc.
- Disadvantages of Serialization.
1. Serialization is default serialization so unnecessary we
have to implement full serialization.
2. Serialization is inefficient when it comes to memory
utilization.
3. Sometimes the byte stream does not convert into objects
completely which leads to error.
 
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What is Serialization? Explain the need of serialization?
- Serialization is a process of converting the state of
object into byte stream.
- Serialization takes care by JVM.
- In Serialization it’s mandatory to save total object.
- Need for the serialization is as follow:
1. Transfer the state of object through the network.
2. Can save the state of object into file.
- Please refer to the below example.
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package simplifiedjava.crackedInterview; import java.io.Serializable; public class Student implements Serializable {
private int id;
private static
String name; private String dept;
public
Student(int id, String name, String dept) {
super();
this.id
= id;
this.name
= name;
this.dept
= dept;
}
public int
getId() {
return id;
}
public void
setId(int id) {
this.id
= id; }
public
String getName() {
return name;
}
public void
setName(String name) {
this.name
= name;
}
public
String getdept() {
return dept;
}
public void
setdept(String dept) {
this.dept
= dept;
} } 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 SerializationDemo { public static void main(String[] args) throws IOException, ClassNotFoundException { Student s1 = new Student(100,"Yogesh","IT");
File file1
= new
File("stud1.ser");
FileOutputStream fos
= new
FileOutputStream(file1);
ObjectOutputStream oos
= new
ObjectOutputStream(fos); oos.writeObject(s1);
File file2
= new
File("stud1.ser");
FileInputStream fis
= new
FileInputStream(file2);
ObjectInputStream ois
= new
ObjectInputStream(fis); Student s2 = (Student) ois.readObject();
System.out.println("Student ID :"
+ s2.getId());
System.out.println("Student Name :"+ s2.getName());
System.out.println("Student Dept :"+ s2.getdept());
}
}
Output:
Student ID :100
Student Name :Yogesh
Student Dept :IT |
What is deserialization?
- Deserialization is the reverse process of
serialization.
- The reverse process of creating the object from a stored
sequence of bytes.
- Please refer to the above example for deserialization.
What are the methods used for Serialization and Deserialization?
- For Serialization we have to use
writeObject() method which belongs to ObjectOutputStream.
- For Deserialization we have to use
readObject() method which belongs to ObjectInputStream.
What is SerialVersionUID? Who provides this SerialVersionUID? How will you create it?
- SerialVersionUID is a unique identifier of the class.
- SerialVersionUID represent the version of the class. This
comes into the picture while serialization and deserialization.
- JVM uses it to compare the versions of the class ensuring
that the same class was used during Serialization is loaded during
Deserialization.
- the default serialVersionUID computation is highly
sensitive to class details that may vary depending on compiler
implementations, and can thus result in unexpected InvalidClassExceptions
during deserialization.
- You can refer the below image to generate the SerialVerionUID.
What is the Externalization? What is the role of Externalizable interface?
- Externalization is customizing serialization.
- In Serialization, it’s always possible to save the total
object to the file and it’s not possible to save part of the object which
may create a performance issue. To cover come to this issue we should go
for externalization.
- In externalization, everything takes care of by the
programmer and JVM doesn’t have any control over it.
- Please refer the blelow example.
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package simplifiedjava.crackedInterview;
import
java.io.Externalizable;
import
java.io.IOException;
import
java.io.ObjectInput; import java.io.ObjectOutput; public class Account implements Externalizable{
long accountId;
String userName;
int pin; int token;
public
Account() {
super();
}
public
Account(long accountId, String userName, int pin, int token) {
super();
this.accountId
= accountId;
this.userName
= userName;
this.pin
= pin;
this.token
= token; }
@Override
public void
writeExternal(ObjectOutput oos) throws
IOException {
oos.writeLong(accountId);
oos.writeObject(userName);
oos.writeInt(pin); }
@Override
public void
readExternal(ObjectInput ois) throws
IOException, ClassNotFoundException {
long accountIdV1
= (long)ois.readLong();
String userNameV1 = (String)ois.readObject();
int pinV1
= (int)ois.readInt();
}
}
package
simplifiedjava.crackedInterview;
import
java.io.FileInputStream;
import
java.io.FileOutputStream;
import
java.io.IOException;
import
java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class ExternalizationDemo {
public static void
main(String[] args) throws
IOException, ClassNotFoundException { Account account = new Account(1001L,"Yogesh Sanas",5555,9800);
FileOutputStream fos
= new
FileOutputStream("acc.ser");
ObjectOutputStream oos
= new
ObjectOutputStream(fos); oos.writeObject(account);
FileInputStream fis
= new
FileInputStream("acc.ser");
ObjectInputStream ois
= new
ObjectInputStream(fis); Account accountV1 = (Account)ois.readObject();
System.out.println(accountV1.accountId);
System.out.println(accountV1.userName);
System.out.println(accountV1.pin); System.out.println(accountV1.token);
System.out.println(account);
}
} |
What are the methods used for Externalization?
- There are couple of methods which are used in
Externalization Interface.
1. writeExternal():This method can be used to write the
custom object for serialization.
2. readExternal():This method can be used to read
the custom object either from the network or file.
What is marker interface? Can you tell me the examples of marker interface?
- Empty interfaces are called marker interfaces.
- Marker interfaces don’t have any method, variable or
constant.
- Marker interfaces are used to inform the JVM that a class
implementing this interface will have some special behaviour.
- There are some marker interfaces in java which are as
follows.
1. Serializable Interface.
2. Clonable Interface.
3. Remote Interface.
4. ActionListener Interface.
What is the difference between Serialization and Externalization?
|
|
Serialization |
Externalization |
|
1. |
Serialization is default Serialization. |
Externalization is customizing Serialization. |
|
2. |
Everything takes care of by JVM in serialization. |
Everything takes care of by the Programmer in
Externalization. |
|
3. |
Serialization is not capable to save the required part of the
object. |
It’s also possible to save part of the object or full object in
Externalization. |
|
4. |
Performance is low as compared to Externalization. |
Performance is high as compared to serialization. |
|
5. |
If you want to serialize a full object then serialization is a
good option. |
If you want to serialize a partial object then externalization is
a good option. |
|
6. |
For serialization, we have to implement a Serializable
interface. |
For externalization, we have to implement an Externalizable
interface. |
|
7. |
The transient keyword is required if you don’t want to make a
particular field serialize. |
The transient keyword is not required because this is customizing
serialization. |
|
8. |
A No-arg constructor is not required. |
A No-arg constructor is required at the time of deserialization
otherwise we will get InvalidClassException. |
- 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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