Part 2
Interview questions on serialization in java for experienced covered in this post:
What are the steps for Serialization, Say suppose I want to serialize Employee
Object?
-
Create Employee class.
-
Implement a Serializable interface.
-
Define some fields.
-
Provide getters and setter methods.
-
Please refer to the below example.
|
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 |
Can you serialize primitive data types?
-
Yes, All primitives data types are part of Serialization.
 
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Can you serialize private and static variables?
-
Private Variable:
We can serialize private variables. There is no concern at all whether a
variable is private, public or protected. It is simply used for
serialization because it’s a part of an object.
-
Static Variable:
Static variables belong to a class, not an object. So static variables are
not a part of the object state. So static variables cannot consider for
serialization.
How can you prevent particular variable to be serialized?
-
Transient keyword can be used to prevent a particular
variable to be serialized.
-
You can declare the variable as static. Static variables are
not considered for serialization.
-
Please refer to the below example.
|
package simplifiedjava.crackedInterview; import java.io.Serializable; public class Student implements Serializable {
private
static
final
long
serialVersionUID
= 1L;
private
int
id;
private
transient
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 :null – This is not considered for
serialization. Student Dept :IT |
Can I apply transient keyword to primitive, static and reference
variables?
-
Primitive Variables:
transient keyword is applicable to primitive variables.
-
Static Variables:
technically you can declare static variable as a transient but, it doesn’t
make a sense to make static variable as a transient because, transient key
word is used when you don’t want to consider a particular field for
serialization. Static variables by default not considered for serialization.
-
Reference variable: Reference variable can be null and this variable doesn’t have any value
it has an address. So transient keyword is not applicable to reference
variables.
If your child class is Serializable and parent class is not and child class is inheriting some properties of parent class, in that case can you serialize child class?
-
Yes, In that case, we can serialize the child class object.
-
But while serialization, JVM will ignore the original value
of parent class instance variables and save the default value to file.
-
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 default(no-arg) 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; 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.Serializable; public class Child extends Parent implements Serializable{ 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(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(c2.i
+" and "+ c2.j);
}
}
Output:
Values Before Serialization : 10 and 20
Parent Class no-arg constructor called.
Values After Deserialization : 0 and 20 |
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