Interview questions on serialization in java for experienced

October 22, 2022

 Part 4

Interview questions on serialization in java for experienced covered in this post:

    Interview questions on serialization in java for experienced

        Which changes are considered compatible and incompatible in serialization mechanism?

    -          Compatible Changes are as follows.

    1.       Changing access modifier: If you change public, protected, default, private there will be no effect on serialization.

    2.       Adding New fields: Adding new fields is also compatible. There is no restriction to adding new fields in serialization.

    3.       Changing the field from static to non-static: It is kind of adding new fields in serialization.

    4.       Changing the field from transient to non-transient: If you are removing the transient keyword then that field will be eligible for serialization. It’s like adding a new field that is compatible with change.

     

    -          Incompatible Changes are as follows.

    1.       Changing the field from non-static to static: It is equivalent to deletion of the filed.

    2.       Changing the field from non-transient to transient: It is equivalent to deletion of the field.

     

        Can we transfer object through network if serialization mechanism is not available?

    -          Yes, we can transfer object through network if serialization mechanism is not available.

    1.       JSON: We can convert the java object into JSON object. JSON object can be transferred through the network.

    2.       XML: We can convert the java object into XML and then we can transfer through the network.


     

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        Can we serialize the class if class has some collection objects like List, Map and Set?

    -          Yes, we can serialize the collection objects like List, Map and Set.

    -          All collections object implements a Serializable interface.

    -          Please refer to the below example.

    package simplifiedjava.crackedInterview; 

    import java.io.Serializable;

    import java.util.List;

    import java.util.Map;

    import java.util.Set; 

    public class MyCollection implements Serializable{ 

          List<String> myList;

          Set<String> mySet;

          Map<Integer,String> myMap;     

          public MyCollection(List<String> myList, Set<String> mySet,Map<Integer,String> myMap) {

                this.myList = myList;

                this.mySet = mySet;

                this.myMap = myMap;

          } 

          @Override

          public String toString() {

                return "MyCollection [myList=" + myList + ", mySet=" + mySet + ", myMap=" + myMap + "]";

          }    

    } 

    package simplifiedjava.crackedInterview; 

    import java.io.FileInputStream;

    import java.io.FileOutputStream;

    import java.io.IOException;

    import java.io.ObjectInputStream;

    import java.io.ObjectOutputStream;

    import java.util.ArrayList;

    import java.util.HashMap;

    import java.util.HashSet;

    import java.util.List;

    import java.util.Map;

    import java.util.Set; 

    public class SerializeCollectionObjectsDemo { 

          public static void main(String[] args) throws IOException, ClassNotFoundException {           

                List<String> myList = new ArrayList<String>();

                Set<String> mySet = new HashSet<String>();

                Map<Integer,String> myMap = new HashMap<Integer,String>();         

                myList.add("One");

                myList.add("Two");

                myList.add("Three");           

                mySet.add("Four");

                mySet.add("Five");

                mySet.add("Six");           

                myMap.put(1, "One");

                myMap.put(2, "Two");

                myMap.put(3, "Three"); 

                MyCollection collection = new MyCollection(myList, mySet, myMap);           

                FileOutputStream fos = new FileOutputStream("coll.ser");

                ObjectOutputStream oos = new ObjectOutputStream(fos);

                oos.writeObject(collection);           

                FileInputStream fis = new FileInputStream("coll.ser");

                ObjectInputStream ois = new ObjectInputStream(fis);

                MyCollection updatedCollection = (MyCollection)ois.readObject();           

                System.out.println(updatedCollection);           

          }

    }

    Output: MyCollection [myList=[One, Two, Three], mySet=[Five, Six, Four], myMap={1=One, 2=Two, 3=Three}]

        

        Can you Serialize Singleton class and at the time of deserialization object should be in the same state as it was during serialization?

    -          Yes, we can serialize the singleton class.

    -          An object returned by deserialization process is in same state as it was during the serialization process.

    -           We can implement readResolve() method to ensure that we don’t break singleton pattern during deserialization.

    -          Signature of readResolve() method.

    private Object readResolve() throws ObjectStreamException {

          return INSTANCE;

     }

     

    -          You have to define readObject() as well instead of creating new object.

     private void readObject(ObjectInputStream ois) throws IOException,ClassNotFoundException{

           ois.defaultReadObject();

           synchronized (SingletonClass.class) {

            if (INSTANCE == null) {

                  INSTANCE = this;

            }

         }

     } 

     

        Can you tell me any purpose to Serialize Singleton Class?

    -          Serialization is one technique to break the singleton design pattern.

    -          Suppose you serialize the singleton object and then if you de-serialize that object, it will create a new instance, hence breaking the singleton design pattern.

     

        Why java.lang.Object class doesn't implement Serializable interface?

    -          Serializable is marker interface, which is empty, but when a class is marked Serializable that means its objects are Serializable.

    -          The reason the java.lang.Object didn’t implement Serializable is because, what if you do not want to make certain fields as Serializable and you may missed to add transient to that field, then will be a havoc.

    -          By making the programmer implement Serializable for his class, it makes awareness among the programmer that he has consciously implemented it, and should take necessary steps to prevent anything to be serialized which should not be.

     

        What are the callback methods? What is the purpose of callback methods? Can you tell me the examples of callback methods?

    -          A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.




    • Java interview questions and answers all MNC - Click here
    • Basic core java interview questions and answers for freshers - Click here
    • Core java interview questions for 3 years experience - Click here
    • Core java interview questions and answers for 3-5 years exp - Click here
    • Core java interview questions and Answers for 5 - 7 Years exp - Click here
    • Basic Java Interview Questions and Answers - Click here
    • Java interview questions and answers on oops - Click here
    • Java interview questions and answers on Strings - Click here
    • Java interview questions on exception handling - Click here
    • Interview questions on multithreading in java for experienced - Click here
    • Interview questions on serialization in java for experienced - Click here

    • Interview questions on inner class in java for experienced - Click here
    • Interview questions on Collections in java for experienced - Click here


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