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The Java Interview Handbook: 300+ Interview Questions

More on Serialization

Explore advanced serialization concepts in Java, including why non-static inner classes shouldn't implement Serializable, the role of serialVersionUID, and how superclass constructors affect serialization. Understand how to manage member object serialization and subclass behavior to ensure robust serialized forms.

We'll cover the following...
1.

Explain the Externalizable interface.

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1 / 2
Technical Quiz
1.

Consider the following class setup:

class Course {

    String company;

   private Course() { } 

    Course(String company) {
        this.company = company;
    }
}

class EducativeCourse extends Course implements Serializable {

    public EducativeCourse(String authorName) {
        super("Educative");
        this.authorName = authorName;
    }

    private String authorName;
}

Can we serialize the class EducativeCourse ?

A.

Yes

B.

No

1 / 1
Java
import java.io.*;
class Demonstration {
    public static void main( String args[] ) throws Exception {
        EducativeCourse course = new EducativeCourse("C. H. Afzal");
        // Serialization code
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try (ObjectOutput out = new ObjectOutputStream(bos)) {
            out.writeObject(course);
            out.flush();
        } catch (Exception e) {
            throw e;
        }
        byte[] courseInBytes = bos.toByteArray();
        // Deserialization code
        ByteArrayInputStream bis = new ByteArrayInputStream(courseInBytes);
        try (ObjectInput in = new ObjectInputStream(bis)) {
            EducativeCourse deserializeCourse = (EducativeCourse) in.readObject();
            System.out.println(deserializeCourse.company);
        } catch (Exception e) {
            throw e;
        }
    }
}
class Course {
    String company;
    private Course() {
    }
    Course(String company) {
        this.company = company;
    }
}
class EducativeCourse extends Course implements Serializable {
    public EducativeCourse(String authorName) {
        super("Educative");
        this.authorName = authorName;
    }
    private String authorName;
}
Technical Quiz
1.

If we make the parameterless constructor of the super class Course public, the subtype EducativeCourse would become serializable. What would be printed from the following sequence: 

    // 1. Serialize an object of EducativeCourse
   
   //  2. Deserialize the same object back

   //  3. Print the company name like so
           System.out.println(object.company)
A.

Educative

B.

empty string

C.

null

1 / 1
Java
import java.io.*;
class Demonstration {
    public static void main( String args[] ) throws Exception {
        EducativeCourse course = new EducativeCourse("C. H. Afzal");
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try (ObjectOutput out = new ObjectOutputStream(bos)) {
            out.writeObject(course);
            out.flush();
        } catch (Exception e) {
            throw e;
        }
        byte[] courseInBytes = bos.toByteArray();
        ByteArrayInputStream bis = new ByteArrayInputStream(courseInBytes);
        try (ObjectInput in = new ObjectInputStream(bis)) {
            // Deserializing the same object we just serialized
            EducativeCourse deserializeCourse = (EducativeCourse) in.readObject();
            // Printing the superclass's variable
            System.out.println(deserializeCourse.company);
        } catch (Exception e) {
            // Ignore exception, not to be done in production
            System.out.println(e);
        }
    }
}
class Course {
    String company;
    // Default constructor is now public
    public Course() {
    }
    Course(String company) {
        this.company = company;
    }
}
class EducativeCourse extends Course implements Serializable {
    public EducativeCourse(String authorName) {
        super("Educative");
        this.authorName = authorName;
    }
    private String authorName;
}

  • Non-static nested classes (inner classes) shouldn't implement the Serializable ...