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Top X Coffee Serialization Interview Questions Together With Answers

What is Serialization inward Java
Java Serialization is i of of import concept but it’s been rarely used as persistence solution as well as developer by as well as large overlooked Java serialization API. As per my experience Java Serialization is quite an of import theme inward whatever nitty-gritty Java interview, In almost all the interview I lead hold faced at that topographic point are i or 2 Java serialization questions as well as I lead hold seen an interview where after few enquiry on serialization candidate outset feeling uncomfortable because of lack of experience inward this area. They don’t know How to serialize an object inward Java or they are non familiar amongst whatever Java Serialization instance to explain, forget virtually questions similar how Serialization plant inward Java,  Difference betwixt transient as well as volatile variable, How many methods Serializable interface has? what is maker interface? what is the work of marking interface? What is the deviation betwixt Externalizable as well as Serializable inward Java, or after the introduction of annotation, why non coffee replaced Serializable amongst @Serializable annotation or.


In this article, nosotros volition enquiry from both beginner as well as advanced level, which tin endure as beneficial to freshers, novel comers as well as senior Java developers amongst some years of Java evolution experience.

10 Interview questions on Serialization inward Java

Most commercial projection uses either database or retentiveness mapped file or exactly apartment file for at that topographic point persistence requirement as well as solely few of them rely on serialization procedure inward Java. Anyway this post service is non a Java serialization tutorial or how to serialize object inward coffee but virtually interview questions or so serialization machinery as well as Serialization API, Which is worth to lead hold a hold back earlier going for whatever Java or J2EE interview as well as surprising yourself amongst some unknown contents. for those who are non familiar virtually coffee Serialization "Java serialization is the procedure which is used to serialize object inward coffee past times storing object’s soil into a file amongst extension .ser as well as recreating object's soil from that file, this opposite procedure is called deserialization.

The Java Serialization API provides a criterion machinery for developers to lead hold object serialization using Serializable as well as Externalizable interface. By the agency this article is inward continuation of my previous article Top twenty blueprint pattern interview questions,  and 10 Interview questions on Singleton Pattern inward Java So hither nosotros go.

What is Serialization inward Java

Object Serialization inward Java is a procedure used to convert Object into a binary format which tin endure persisted into disk or sent over network to whatever other running Java virtual machine; the opposite procedure of creating object from binary flow is called deserialization inward Java. Java provides Serialization API for serializing as well as deserializing object which includes java.io.Serializable, java.io.Externalizable, ObjectInputStream as well as ObjectOutputStream etc. Java programmers are gratis to work default Serialization machinery which Java uses based upon construction of shape but they are also gratis to work at that topographic point ain custom binary format, which is often advised as Serialization best practice, Because serialized binary format becomes business office of Class's exported API as well as it tin potentially intermission Encapsulation inward Java provided past times person as well as package-private fields. This pretty much respond the enquiry What is Serialization inward Java.

How to brand a Java shape Serializable?

Making a shape Serializable inward Java is real easy, Your Java shape exactly needs to implements java.io.Serializable interface as well as JVM volition accept help of serializing object inward default format. Decision to making a Class Serializable should endure taken concisely because though close term damage of making a Class Serializable is low, long term damage is substantial as well as it tin potentially trammel your mightiness to farther modify as well as alter its implementation because similar whatever populace API, serialized shape of an object becomes business office of populace API as well as when you lot alter construction of your shape past times implementing improver interface, adding or removing whatever patch tin potentially intermission default serialization, this tin endure minimized past times using a custom binary format but withal requires lot of attempt to ensure backward compatibility. One instance of How Serialization tin seat constraints on your mightiness to alter shape is SerialVersionUID. If you lot don't explicitly declare SerialVersionUID so JVM generates its based upon construction of shape which depends upon interfaces a shape implements as well as several other factors which is dependent area to change. Suppose you lot implement some other interface than JVM volition generate a unlike SerialVersionUID for novel version of shape files as well as when you lot essay to charge erstwhile object object serialized past times erstwhile version of your programme you lot volition acquire InvalidClassException.

Question 1) What is the deviation betwixt Serializable as well as Externalizable interface inward Java?

This is most oft asked enquiry inward Java serialization interview. Here is my version Externalizable provides us writeExternal() as well as readExternal() method which gives us flexibility to command coffee serialization machinery instead of relying on Java's default serialization. Correct implementation of Externalizable interface tin improve functioning of application drastically.

Question 2) How many methods Serializable has? If no method so what is the work of Serializable interface?

Serializable interface exists inward java.io parcel as well as forms nitty-gritty of coffee serialization mechanism. It doesn't lead hold whatever method as well as also called Marker Interface inward Java. When your shape implements java.io.Serializable interface it becomes Serializable inward Java as well as gives compiler an indication that work Java Serialization machinery to serialize this object.

Question 3) What is serialVersionUID? What would move on if you lot don't define this?

One of my favorite enquiry interview enquiry on Java serialization. SerialVersionUID is an ID which is stamped on object when it acquire serialized usually hashcode of object, you lot tin work tool serialver to meet serialVersionUID of a serialized object . SerialVersionUID is used for version command of object. you lot tin specify serialVersionUID inward your class file also. Consequence of non specifying serialVersionUID is that when you lot add together or modify whatever patch inward shape so already serialized shape volition non endure able to recover because serialVersionUID generated for novel shape as well as for erstwhile serialized object volition endure different. Java serialization procedure relies on right serialVersionUID for recovering soil of serialized object as well as throws java.io.InvalidClassException inward instance of serialVersionUID mismatch, to larn to a greater extent than virtually serialversionuid meet this article.

Question 4) While serializing you lot desire some of the members non to serialize? How do you lot plough over it?

Another oft asked Serialization interview question. This is sometime also asked as what is the work of transient variable, does transient as well as static variable gets serialized or non etc. so if you lot don't desire whatever patch to endure business office of object's soil so declare it either static or transient based on your demand as well as it volition non endure included during Java serialization process.

Question 5) What volition move on if i of the members inward the shape doesn't implement Serializable interface?

One of the tardily enquiry virtually Serialization procedure inward Java. If you lot essay to serialize an object of a shape which implements Serializable, but the object includes a reference to an non- Serializable shape so a ‘NotSerializableException’ volition endure thrown at runtime as well as this is why I ever seat a SerializableAlert (comment department inward my code) , i of the code comment best practices, to learn developer to recall this fact spell adding a novel patch inward a Serializable class.

Question 6) If a shape is Serializable but its super shape inward not, what volition endure the soil of the instance variables inherited from super shape after deserialization?

Java serialization procedure solely continues inward object hierarchy till the shape is Serializable i.e. implements Serializable interface inward Java as well as values of the instance variables inherited from super shape volition endure initialized past times calling constructor of Non-Serializable Super shape during deserialization process. Once the constructor chaining volition started it wouldn't endure possible to halt that , thus fifty-fifty if classes higher inward hierarchy implements Serializable interface , at that topographic point constructor volition endure executed. As you lot meet from the contention this Serialization interview enquiry looks real tricky as well as tough but if you lot are familiar amongst fundamental concepts its non that difficult.

Question 7) Can you lot Customize Serialization procedure or tin you lot override default Serialization procedure inward Java?

The respond is aye you lot can. We all know that for serializing an object ObjectOutputStream.writeObject (saveThisobject) is invoked as well as for reading object ObjectInputStream.readObject() is invoked but at that topographic point is i to a greater extent than affair which Java Virtual Machine provides you lot is to define these 2 method inward your class. If you lot define these 2 methods inward your shape so JVM volition invoke these 2 methods instead of applying default serialization mechanism. You tin customize demeanour of object serialization as well as deserialization hither past times doing whatever sort of pre or post service processing task. Important betoken to depository fiscal establishment complaint is making these methods person to avoid existence inherited, overridden or overloaded. Since solely Java Virtual Machine tin telephone phone person method integrity of your shape volition rest as well as Java Serialization volition run as normal. In my sentiment this is i of the best enquiry i tin inquire inward whatever Java Serialization interview, a expert follow-up enquiry is why should you lot supply custom serialized shape for your object?

Question 8) Suppose super shape of a novel shape implement Serializable interface, how tin you lot avoid novel shape to existence serialized?

One of the tricky interview enquiry inward Serialization inward Java. If Super Class of a Class already implements Serializable interface inward Java so its already Serializable inward Java, since you lot tin non unimplemented an interface its non actually possible to acquire inward Non Serializable shape but aye at that topographic point is a agency to avoid serialization of novel class. To avoid Java serialization you lot demand to implement writeObject() as well as readObject() method inward your Class as well as demand to throw NotSerializableException from those method. This is some other do goodness of customizing coffee serialization procedure as described inward in a higher house Serialization interview question as well as commonly it asked as follow-up enquiry as interview progresses.

Question 9) Which methods are used during Serialization as well as DeSerialization procedure inward Java?

This is real mutual interview enquiry inward Serialization basically interviewer is trying to know; Whether you lot are familiar amongst usage of readObject(), writeObject(), readExternal() as well as writeExternal() or not. Java Serialization is done past times java.io.ObjectOutputStream class. That shape is a filter flow which is wrapped or so a lower-level byte flow to lead hold the serialization mechanism. To shop whatever object via serialization machinery nosotros telephone phone ObjectOutputStream.writeObject(saveThisobject) as well as to deserialize that object nosotros telephone phone ObjectInputStream.readObject() method. Call to writeObject() method trigger serialization procedure inward java. i of import affair to depository fiscal establishment complaint virtually readObject() method is that it is used to read bytes from the persistence as well as to create object from those bytes as well as its render an Object which needs to endure type cast to right type.

Question 10) Suppose you lot lead hold a shape which you lot serialized it as well as stored inward persistence as well as afterward modified that shape to add together a novel field. What volition move on if you lot deserialize the object already serialized?

It depends on whether shape has its ain serialVersionUID or not. As nosotros know from inward a higher house enquiry that if nosotros don't supply serialVersionUID inward our code coffee compiler volition generate it as well as commonly it’s equal to hashCode of object. past times adding whatever novel patch at that topographic point is run a hazard that novel serialVersionUID generated for that shape version is non the same of already serialized object as well as inward this instance Java Serialization API volition throw java.io.InvalidClassException as well as this is the argue its recommended to lead hold your ain serialVersionUID inward code as well as brand certain to maintain it same ever for a unmarried class.

11) What are the compatible changes as well as incompatible changes inward Java Serialization Mechanism?

The existent challenge lies amongst alter inward shape construction past times adding whatever field, method or removing whatever patch or method is that amongst already serialized object. As per Java Serialization specification adding whatever patch or method comes nether compatible alter as well as changing shape hierarchy or UN-implementing Serializable interfaces some nether non compatible changes. For consummate listing of compatible as well as non compatible changes I would propose reading Java serialization specification.

12) Can nosotros transfer a Serialized object vie network?

Yes you lot tin transfer a Serialized object via network because Java serialized object remains inward shape of bytes which tin endure transmitter via network. You tin also shop serialized object inward Disk or database as Blob.

13) Which sort of variables is non serialized during Java Serialization?

This enquiry asked sometime differently but the work is same whether Java developer knows specifics virtually static as well as transient variable or not. Since static variables belong to the shape as well as non to an object they are non the business office of the soil of object so they are non saved during Java Serialization process. As Java Serialization solely persist soil of object as well as non object itself. Transient variables are also non included inward coffee serialization procedure as well as are non the business office of the object’s serialized state. After this enquiry sometime interviewer inquire a follow-up if you lot don't shop values of these variables so what would endure value of these variable i time you lot deserialize as well as recreate those object? This is for you lot guys to think virtually .

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