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More on Serialization

More on Serialization

More questions on Serialization in Java.

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1.

Explain the Externalizable interface.

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Q1 / Q2
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

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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
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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 ...