Top Ten Coffee Serialization Interview Questions As Well As Answers

What is Serialization inward Java
Java Serialization is i of of import concept but it’s been rarely used as persistence solution too developer by too large overlooked Java serialization API. As per my experience Java Serialization is quite an of import topic inward whatsoever substance Java interview, In almost all the interview I receive got faced at that spot are i or 2 Java serialization questions too I receive got seen an interview where after few interrogation on serialization candidate root 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 alongside whatsoever Java Serialization instance to explain, forget nearly questions similar how Serialization plant inward Java,  Difference betwixt transient too volatile variable, How many methods Serializable interface has? what is maker interface? what is the purpose of mark interface? What is the departure betwixt Externalizable too Serializable inward Java, or after the introduction of annotation, why non coffee replaced Serializable alongside @Serializable annotation or.


In this article, nosotros volition interrogation from both beginner too advanced level, which tin ship away last as beneficial to freshers, novel comers too senior Java developers alongside 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 spot persistence requirement too entirely few of them rely on serialization procedure inward Java. Anyway this ship service is non a Java serialization tutorial or how to serialize object inward coffee but nearly interview questions closed to serialization machinery too Serialization API, Which is worth to receive got a await earlier going for whatsoever Java or J2EE interview too surprising yourself alongside some unknown contents. for those who are non familiar nearly coffee Serialization "Java serialization is the procedure which is used to serialize object inward coffee past times storing object’s Blue Planet into a file alongside extension .ser too recreating object's Blue Planet from that file, this opposite procedure is called deserialization.

The Java Serialization API provides a measure machinery for developers to guide hold object serialization using Serializable too Externalizable interface. By the agency this article is inward continuation of my previous article Top xx pattern 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 ship away last persisted into disk or sent over network to whatsoever 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 too deserializing object which includes java.io.Serializable, java.io.Externalizable, ObjectInputStream too ObjectOutputStream etc. Java programmers are complimentary to usage default Serialization machinery which Java uses based upon construction of shape but they are also complimentary to usage at that spot ain custom binary format, which is often advised as Serialization best practice, Because serialized binary format becomes purpose of Class's exported API too it tin ship away potentially pause Encapsulation inward Java provided past times mortal too package-private fields. This pretty much respond the interrogation 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 too JVM volition accept attention of serializing object inward default format. Decision to making a Class Serializable should last taken concisely because though nigh term damage of making a Class Serializable is low, long term damage is substantial too it tin ship away potentially restrict your mightiness to farther modify too alter its implementation because similar whatsoever world API, serialized shape of an object becomes purpose of world API too when y'all alter construction of your shape past times implementing add-on interface, adding or removing whatsoever acre tin ship away potentially pause default serialization, this tin ship away last minimized past times using a custom binary format but all the same requires lot of endeavor to ensure backward compatibility. One instance of How Serialization tin ship away pose constraints on your mightiness to alter shape is SerialVersionUID. If y'all don't explicitly declare SerialVersionUID so JVM generates its based upon construction of shape which depends upon interfaces a shape implements too several other factors which is dependent acre to change. Suppose y'all implement some other interface than JVM volition generate a dissimilar SerialVersionUID for novel version of shape files too when y'all seek to charge onetime object object serialized past times onetime version of your programme y'all volition acquire InvalidClassException.

Question 1) What is the departure betwixt Serializable too Externalizable interface inward Java?

This is most often asked interrogation inward Java serialization interview. Here is my version Externalizable provides us writeExternal() too 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 ship away improve surgery of application drastically.

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

Serializable interface exists inward java.io packet too forms substance of coffee serialization mechanism. It doesn't receive got whatsoever method too also called Marker Interface inward Java. When your shape implements java.io.Serializable interface it becomes Serializable inward Java too gives compiler an indication that usage Java Serialization machinery to serialize this object.

Question 3) What is serialVersionUID? What would come about if y'all don't define this?

One of my favorite interrogation interview interrogation on Java serialization. SerialVersionUID is an ID which is stamped on object when it acquire serialized usually hashcode of object, y'all tin ship away usage tool serialver to run into serialVersionUID of a serialized object . SerialVersionUID is used for version command of object. y'all tin ship away specify serialVersionUID inward your class file also. Consequence of non specifying serialVersionUID is that when y'all add together or modify whatsoever acre inward shape so already serialized shape volition non last able to recover because serialVersionUID generated for novel shape too for onetime serialized object volition last different. Java serialization procedure relies on right serialVersionUID for recovering Blue Planet of serialized object too throws java.io.InvalidClassException inward instance of serialVersionUID mismatch, to larn to a greater extent than nearly serialversionuid run into this article.

Question 4) While serializing y'all desire some of the members non to serialize? How do y'all attain it?

Another often asked Serialization interview question. This is sometime also asked as what is the usage of transient variable, does transient too static variable gets serialized or non etc. so if y'all don't desire whatsoever acre to last purpose of object's Blue Planet so declare it either static or transient based on your demand too it volition non last included during Java serialization process.

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

One of the slow interrogation nearly Serialization procedure inward Java. If y'all seek 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 last thrown at runtime too this is why I ever pose a SerializableAlert (comment department inward my code) , i of the code comment best practices, to teach developer to retrieve this fact spell adding a novel acre inward a Serializable class.

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

Java serialization procedure entirely continues inward object hierarchy till the shape is Serializable i.e. implements Serializable interface inward Java too values of the instance variables inherited from super shape volition last initialized past times calling constructor of Non-Serializable Super shape during deserialization process. Once the constructor chaining volition started it wouldn't last possible to halt that , thus fifty-fifty if classes higher inward hierarchy implements Serializable interface , at that spot constructor volition last executed. As y'all run into from the disputation this Serialization interview interrogation looks real tricky too tough but if y'all are familiar alongside fundamental concepts its non that difficult.

Question 7) Can y'all Customize Serialization procedure or tin ship away y'all override default Serialization procedure inward Java?

The respond is aye y'all can. We all know that for serializing an object ObjectOutputStream.writeObject (saveThisobject) is invoked too for reading object ObjectInputStream.readObject() is invoked but at that spot is i to a greater extent than affair which Java Virtual Machine provides y'all is to define these 2 method inward your class. If y'all define these 2 methods inward your shape so JVM volition invoke these 2 methods instead of applying default serialization mechanism. You tin ship away customize behaviour of object serialization too deserialization hither past times doing whatsoever variety of pre or ship service processing task. Important request to complaint is making these methods mortal to avoid beingness inherited, overridden or overloaded. Since entirely Java Virtual Machine tin ship away telephone telephone mortal method integrity of your shape volition rest too Java Serialization volition move as normal. In my catch this is i of the best interrogation i tin ship away enquire inward whatsoever Java Serialization interview, a skilful follow-up interrogation is why should y'all supply custom serialized shape for your object?

Question 8) Suppose super shape of a novel shape implement Serializable interface, how tin ship away y'all avoid novel shape to beingness serialized?

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

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

This is real mutual interview interrogation inward Serialization basically interviewer is trying to know; Whether y'all are familiar alongside usage of readObject(), writeObject(), readExternal() too writeExternal() or not. Java Serialization is done past times java.io.ObjectOutputStream class. That shape is a filter flow which is wrapped closed to a lower-level byte flow to guide hold the serialization mechanism. To shop whatsoever object via serialization machinery nosotros telephone telephone ObjectOutputStream.writeObject(saveThisobject) too to deserialize that object nosotros telephone telephone ObjectInputStream.readObject() method. Call to writeObject() method trigger serialization procedure inward java. i of import affair to complaint nearly readObject() method is that it is used to read bytes from the persistence too to create object from those bytes too its render an Object which needs to last type cast to right type.

Question 10) Suppose y'all receive got a shape which y'all serialized it too stored inward persistence too afterward modified that shape to add together a novel field. What volition come about if y'all deserialize the object already serialized?

It depends on whether shape has its ain serialVersionUID or not. As nosotros know from to a higher house interrogation that if nosotros don't supply serialVersionUID inward our code coffee compiler volition generate it too unremarkably it’s equal to hashCode of object. past times adding whatsoever novel acre at that spot is run a peril that novel serialVersionUID generated for that shape version is non the same of already serialized object too inward this instance Java Serialization API volition throw java.io.InvalidClassException too this is the argue its recommended to receive got your ain serialVersionUID inward code too brand certain to maintain it same ever for a unmarried class.

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

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

12) Can nosotros transfer a Serialized object vie network?

Yes y'all tin ship away transfer a Serialized object via network because Java serialized object remains inward shape of bytes which tin ship away last transmitter via network. You tin ship away also shop serialized object inward Disk or database as Blob.

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

This interrogation asked sometime differently but the purpose is same whether Java developer knows specifics nearly static too transient variable or not. Since static variables belong to the shape too non to an object they are non the purpose of the Blue Planet of object so they are non saved during Java Serialization process. As Java Serialization entirely persist Blue Planet of object too non object itself. Transient variables are also non included inward coffee serialization procedure too are non the purpose of the object’s serialized state. After this interrogation sometime interviewer enquire a follow-up if y'all don't shop values of these variables so what would last value of these variable in i trial y'all deserialize too recreate those object? This is for y'all guys to intend nearly .

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