What is object serialization

Question

What is meant by  object serialization   Can you please explain it with some examples

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Serialization is the process of turning a Java object into byte array and then back into object again with its preserved state. Useful for various things like sending objects over network or caching things to disk.

Read more from this short article which explains programming part of the process quite well and then move over to to Serializable javadoc. You may also be interested in reading this related question.

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You can think of serialization as the process of converting an object instance into a sequence of bytes  which may be binary or not depending on the implementation    It is very useful when you want to transmit one object data across the network  for instance from one JVM to another   In Java  the serialization mechanism is built into the platform  but you need to implement the Serializable interface to make an object serializable   You can also prevent some data in your object from being serialized by marking the attribute as transient   Finally you can override the default mechanism  and provide your own  this may be suitable in some special cases  To do this  you use one of the hidden features in java   It is important to notice that what gets serialized is the  value  of the object  or the contents  and not the class definition  Thus methods are not serialized   Here is a very basic sample with comments to facilitate its reading   import java io    import java util        This class implements  Serializable  to let the system know    it s ok to do it  You as programmer are aware of that  public class SerializationSample implements Serializable           These attributes conform the  value  of the object          These two will be serialized      private String aString    The value of that string       private int    someInteger   0          But this won t since it is marked as transient      private transient List lt File gt  unInterestingLongLongList          Main method to test      public static void main  String    args   throws IOException                 Create a sample object  that contains the default values          SerializationSample instance   new SerializationSample                The  ObjectOutputStream  class has the default             definition to serialize an object          ObjectOutputStream oos   new ObjectOutputStream                                     By using  FileOutputStream  we will                                    Write it to a File in the file system                                   It could have been a Socket to another                                    machine  a database  an in memory array  etc                                 new FileOutputStream new File  o ser                  do the magic           oos writeObject  instance               close the writing          oos close              When we run this program  the file  o ser  is created and we can see what happened behind   If we change the value of  someInteger to  for example Integer MAX VALUE  we may compare the output to see what the difference is   Here s a screenshot showing precisely that difference     Can you spot the differences      There is an additional relevant field in Java serialization  The serialversionUID but I guess this is already too long to cover it

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Return the file as an Object   http   www tutorialspoint com java java serialization htm          import java io             public class SerializeDemo                      public static void main String    args                             Employee e   new Employee                  e name    Reyan Ali                 e address    Phokka Kuan  Ambehta Peer                 e SSN   11122333                e number   101                 try                                  FileOutputStream fileOut                    new FileOutputStream   tmp employee ser                     ObjectOutputStream out   new ObjectOutputStream fileOut                    out writeObject e                    out close                     fileOut close                     System out printf  Serialized data is saved in  tmp employee ser                   catch IOException i                                    i printStackTrace                                                import java io        public class DeserializeDemo              public static void main String    args                     Employee e   null            try                          FileInputStream fileIn   new FileInputStream   tmp employee ser                 ObjectInputStream in   new ObjectInputStream fileIn                e    Employee  in readObject                 in close                 fileIn close               catch IOException i                           i printStackTrace                 return             catch ClassNotFoundException c                           System out println  Employee class not found                 c printStackTrace                 return                        System out println  Deserialized Employee                 System out println  Name      e name             System out println  Address      e address             System out println  SSN      e SSN             System out println  Number      e number

User · Answer

Serialization is the process of turning a Java object into byte array and then back into object again with its preserved state. Useful for various things like sending objects over network or caching things to disk.

Read more from this short article which explains programming part of the process quite well and then move over to to Serializable javadoc. You may also be interested in reading this related question.

User · Answer

Serialization is the process of turning a Java object into byte array and then back into object again with its preserved state. Useful for various things like sending objects over network or caching things to disk.

Read more from this short article which explains programming part of the process quite well and then move over to to Serializable javadoc. You may also be interested in reading this related question.

User · Answer

Serialization is the process of converting an object s state to bits so that it can be stored on a hard drive  When you deserialize the same object  it will retain its state later   It lets you recreate objects without having to save the objects  properties by hand   http   en wikipedia org wiki Serialization

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You can think of serialization as the process of converting an object instance into a sequence of bytes  which may be binary or not depending on the implementation    It is very useful when you want to transmit one object data across the network  for instance from one JVM to another   In Java  the serialization mechanism is built into the platform  but you need to implement the Serializable interface to make an object serializable   You can also prevent some data in your object from being serialized by marking the attribute as transient   Finally you can override the default mechanism  and provide your own  this may be suitable in some special cases  To do this  you use one of the hidden features in java   It is important to notice that what gets serialized is the  value  of the object  or the contents  and not the class definition  Thus methods are not serialized   Here is a very basic sample with comments to facilitate its reading   import java io    import java util        This class implements  Serializable  to let the system know    it s ok to do it  You as programmer are aware of that  public class SerializationSample implements Serializable           These attributes conform the  value  of the object          These two will be serialized      private String aString    The value of that string       private int    someInteger   0          But this won t since it is marked as transient      private transient List lt File gt  unInterestingLongLongList          Main method to test      public static void main  String    args   throws IOException                 Create a sample object  that contains the default values          SerializationSample instance   new SerializationSample                The  ObjectOutputStream  class has the default             definition to serialize an object          ObjectOutputStream oos   new ObjectOutputStream                                     By using  FileOutputStream  we will                                    Write it to a File in the file system                                   It could have been a Socket to another                                    machine  a database  an in memory array  etc                                 new FileOutputStream new File  o ser                  do the magic           oos writeObject  instance               close the writing          oos close              When we run this program  the file  o ser  is created and we can see what happened behind   If we change the value of  someInteger to  for example Integer MAX VALUE  we may compare the output to see what the difference is   Here s a screenshot showing precisely that difference     Can you spot the differences      There is an additional relevant field in Java serialization  The serialversionUID but I guess this is already too long to cover it

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I ll offer an analogy to potentially assist in solidifying the conceptual purpose practicality of object serialization deserialization   I imagine object serialization deserialization in the context of attempting to move an object through a storm drain  The object is essentially  decomposed  or serialized into more modular versions of itself - in this case  a series of bytes - in order to effectively be granted passage through a medium  In a computational sense  we could view the path traveled by the bytes through the storm drain as being akin to bytes traveling through a network  We re transmuting our object in order to conform to a more desirable mode of transportation  or format  The serialized object will typically be stored in a binary file which may later be read from  written to  or both   Perhaps once our object is able to slip through the drain as a decomposed series of bytes  we may wish to store that representation of the object as binary data within a database or hard disk drive  The main takeaway though  is that with serialization deserialization  we have the option to let our object remain in it s binary form after being serialized  or  retrieve  the object s original form by performing deserialization

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Serialization is the conversion of an object to a series of bytes  so that the object can be easily saved to persistent storage or streamed across a communication link  The byte stream can then be deserialized - converted into a replica of the original object

User · Answer

You can think of serialization as the process of converting an object instance into a sequence of bytes  which may be binary or not depending on the implementation    It is very useful when you want to transmit one object data across the network  for instance from one JVM to another   In Java  the serialization mechanism is built into the platform  but you need to implement the Serializable interface to make an object serializable   You can also prevent some data in your object from being serialized by marking the attribute as transient   Finally you can override the default mechanism  and provide your own  this may be suitable in some special cases  To do this  you use one of the hidden features in java   It is important to notice that what gets serialized is the  value  of the object  or the contents  and not the class definition  Thus methods are not serialized   Here is a very basic sample with comments to facilitate its reading   import java io    import java util        This class implements  Serializable  to let the system know    it s ok to do it  You as programmer are aware of that  public class SerializationSample implements Serializable           These attributes conform the  value  of the object          These two will be serialized      private String aString    The value of that string       private int    someInteger   0          But this won t since it is marked as transient      private transient List lt File gt  unInterestingLongLongList          Main method to test      public static void main  String    args   throws IOException                 Create a sample object  that contains the default values          SerializationSample instance   new SerializationSample                The  ObjectOutputStream  class has the default             definition to serialize an object          ObjectOutputStream oos   new ObjectOutputStream                                     By using  FileOutputStream  we will                                    Write it to a File in the file system                                   It could have been a Socket to another                                    machine  a database  an in memory array  etc                                 new FileOutputStream new File  o ser                  do the magic           oos writeObject  instance               close the writing          oos close              When we run this program  the file  o ser  is created and we can see what happened behind   If we change the value of  someInteger to  for example Integer MAX VALUE  we may compare the output to see what the difference is   Here s a screenshot showing precisely that difference     Can you spot the differences      There is an additional relevant field in Java serialization  The serialversionUID but I guess this is already too long to cover it

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Serializing a class   Converting an object to bytes and bytes back to object  Deserialization    class NamCls implements Serializable       int NumVar      String NamVar          Object-Serialization is process of converting the state of an object into steam of bytes     -  Implement when you want the object to exist beyond the lifetime of the JVM   -  Serialized Object can be stored in Database   -  Serializable-objects cannot be read and understood by humans so we can acheive security        Object-Deserialization is the process of getting the state of an object and store it into an object java lang Object      -  Before storing its state it checks whether serialVersionUID form input-file network and  class file serialVersionUID are same   amp nbsp amp nbspIf not throw java io InvalidClassException        A Java object is only serializable  if its class or any of its superclasses   implements either the java io Serializable interface or its subinterface  java io Externalizable        Static fields in a class cannot be serialized   class NamCls implements Serializable       int NumVar      static String NamVar    I won t be serializable            If you do not want to serialise a variable of a class use transient keyword  class NamCls implements Serializable       int NumVar      transient String NamVar          If a class implements serializable then all its sub classes will also be serializable       If a class has a reference of another class  all the references must be Serializable otherwise serialization process will not be performed  In such case NotSerializableException is thrown at runtime

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Serializing a class   Converting an object to bytes and bytes back to object  Deserialization    class NamCls implements Serializable       int NumVar      String NamVar          Object-Serialization is process of converting the state of an object into steam of bytes     -  Implement when you want the object to exist beyond the lifetime of the JVM   -  Serialized Object can be stored in Database   -  Serializable-objects cannot be read and understood by humans so we can acheive security        Object-Deserialization is the process of getting the state of an object and store it into an object java lang Object      -  Before storing its state it checks whether serialVersionUID form input-file network and  class file serialVersionUID are same   amp nbsp amp nbspIf not throw java io InvalidClassException        A Java object is only serializable  if its class or any of its superclasses   implements either the java io Serializable interface or its subinterface  java io Externalizable        Static fields in a class cannot be serialized   class NamCls implements Serializable       int NumVar      static String NamVar    I won t be serializable            If you do not want to serialise a variable of a class use transient keyword  class NamCls implements Serializable       int NumVar      transient String NamVar          If a class implements serializable then all its sub classes will also be serializable       If a class has a reference of another class  all the references must be Serializable otherwise serialization process will not be performed  In such case NotSerializableException is thrown at runtime

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Serialization means persisting objects in java  If you want to save the state of the object and want to rebuild the state later  may be in another JVM  serialization can be used   Note that the properties of an object is only going to be saved  If you want to resurrect the object again you should have the class file  because the member variables only will be stored and not the member functions   eg    ObjectInputStream oos   new ObjectInputStream                                                                    new FileInputStream   new File  o ser        SerializationSample SS    SearializationSample  oos readObject      The Searializable is a marker interface which marks that your class is serializable  Marker interface means that it is just an empty interface and using that interface will notify the JVM that this class can be made serializable

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Serialization is taking a  live  object in memory and converting it to a format that can be stored somewhere  eg  in memory  on disk  and later  deserialized  back into a live object

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Serialization is the conversion of an object to a series of bytes  so that the object can be easily saved to persistent storage or streamed across a communication link  The byte stream can then be deserialized - converted into a replica of the original object

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Serialization means persisting objects in java  If you want to save the state of the object and want to rebuild the state later  may be in another JVM  serialization can be used   Note that the properties of an object is only going to be saved  If you want to resurrect the object again you should have the class file  because the member variables only will be stored and not the member functions   eg    ObjectInputStream oos   new ObjectInputStream                                                                    new FileInputStream   new File  o ser        SerializationSample SS    SearializationSample  oos readObject      The Searializable is a marker interface which marks that your class is serializable  Marker interface means that it is just an empty interface and using that interface will notify the JVM that this class can be made serializable

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Java Object Serialization    Serialization is a mechanism to transform a graph of Java objects into an array of bytes for storage to disk file  or transmission across a network   then by using deserialization we can restore the graph of objects  Graphs of objects are restored correctly using a reference sharing mechanism  But before storing  check whether serialVersionUID from input-file network and  class file serialVersionUID are the same  If not  throw a java io InvalidClassException      Each versioned class must identify the original class version for which it is capable of writing streams and from which it can read  For example  a versioned class must declare       serialVersionUID Syntax     ANY-ACCESS-MODIFIER static final long serialVersionUID    64-bit has L  private static final long serialVersionUID   3487495895819393L       serialVersionUID is essential to the serialization process  But it is optional for the developer to add it into the java source file  If a serialVersionUID is not included  the serialization runtime will generate a serialVersionUID and associate it with the class  The serialized object will contain this serialVersionUID along with other data   Note - It is strongly recommended that all serializable classes explicitly declare a serialVersionUID  since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations  and can thus result in unexpected serialVersionUID conflicts during deserialization  causing deserialization to fail   Inspecting Serializable Classes         A Java object is only serializable  if a class or any of its superclasses implements either the java io Serializable interface     or its subinterface  java io Externalizable     A class must implement java io Serializable interface in order to serialize its object successfully  Serializable is a marker interface and used to inform the compiler that the class implementing it has to be added serializable behavior  Here Java Virtual Machine  JVM  is responsible for its automatic serialization      transient Keyword  java io Serializable interface      While serializing an object  if we don t want certain data members of the object to be serialized we can use the transient modifier  The transient keyword will prevent that data member from being serialized          Fields declared as transient or static are ignored by the serialization process               TRANSIENT  amp  VOLATILE      -------------- -------- -------------------------------------     Flag Name      Value   Interpretation                         -------------- -------- -------------------------------------    ACC VOLATILE   0x0040   Declared volatile  cannot be cached    -------------- -------- -------------------------------------   ACC TRANSIENT   0x0080   Declared transient  not written or                              read by a persistent object manager    -------------- -------- -------------------------------------       class Employee implements Serializable       private static final long serialVersionUID   2L      static int id       int eno       String name      transient String password     Using transient keyword means its not going to be Serialized       Implementing the Externalizable interface allows the object to assume complete control over the contents and format of the object s serialized form  The methods of the Externalizable interface  writeExternal and readExternal  are called to save and restore the objects state  When implemented by a class they can write and read their own state using all of the methods of ObjectOutput and ObjectInput  It is the responsibility of the objects to handle any versioning that occurs      class Emp implements Externalizable       int eno       String name      transient String password     No use of transient  we need to take care of write and read        Override     public void writeExternal ObjectOutput out  throws IOException           out writeInt eno           out writeUTF name             out writeUTF password              Override     public void readExternal ObjectInput in  throws IOException  ClassNotFoundException           this eno   in readInt            this name   in readUTF              this password   in readUTF       java io EOFException            Only objects that support the java io Serializable or java io Externalizable interface can be written to read from streams  The class of each serializable object is encoded including the class name and signature of the class  the values of the object s fields and arrays  and the closure of any other objects referenced from the initial objects     Serializable Example For Files    public class SerializationDemo       static String fileName    D  serializable file ser        public static void main String   args  throws IOException  ClassNotFoundException  InstantiationException  IllegalAccessException           Employee emp   new Employee             Employee id   1     Can not Serialize Class data          emp eno   77          emp name    Yash           emp password    confidential           objects WriteRead emp  fileName            Emp e   new Emp             e eno   77          e name    Yash           e password    confidential           objects WriteRead External e  fileName              String stubHost    127 0 0 1           Integer anyFreePort   7777          socketRead anyFreePort     Thread1         socketWrite emp  stubHost  anyFreePort     Thread2              public static void objects WriteRead  Employee obj  String serFilename   throws IOException          FileOutputStream fos   new FileOutputStream  new File  serFilename              ObjectOutputStream objectOut   new ObjectOutputStream  fos            objectOut writeObject  obj            objectOut close            fos close             System out println  Data Stored in to a file             try               FileInputStream fis   new FileInputStream  new File  serFilename                  ObjectInputStream ois   new ObjectInputStream  fis                Object readObject              readObject   ois readObject                String calssName   readObject getClass   getName                System out println  Restoring Class Name      calssName      InvalidClassException              Employee emp    Employee  readObject              System out format  Obj No  s  Name  s  Pass  s    emp eno  emp name  emp password                ois close              catch  ClassNotFoundException e                e printStackTrace                        public static void objects WriteRead External  Emp obj  String serFilename   throws IOException           FileOutputStream fos   new FileOutputStream new File  serFilename             ObjectOutputStream objectOut   new ObjectOutputStream  fos             obj writeExternal  objectOut            objectOut flush             fos close             System out println  Data Stored in to a file             try                  create a new instance and read the assign the contents from stream              Emp emp   new Emp                 FileInputStream fis   new FileInputStream new File  serFilename                 ObjectInputStream ois   new ObjectInputStream  fis                 emp readExternal ois                System out format  Obj No  s  Name  s  Pass  s    emp eno  emp name  emp password                ois close              catch  ClassNotFoundException e                e printStackTrace                          Serializable Example Over Network  Distributing object s state across different address spaces  either in different processes on the same computer  or even in multiple computers connected via a network  but which work together by sharing data and invoking methods     Data Marshalling Stubs and Skeletons            Creates a stream socket and connects it to the specified port number on the named host       public static void socketWrite Employee objectToSend  String stubHost  Integer anyFreePort        try      CLIENT - Stub marshalling          Socket client   new Socket stubHost  anyFreePort           ObjectOutputStream out   new ObjectOutputStream client getOutputStream             out writeObject objectToSend           out flush            client close          catch  IOException e            e printStackTrace               Creates a server socket  bound to the specified port   public static void socketRead   Integer anyFreePort         try      SERVER - Stub unmarshalling           ServerSocket serverSocket   new ServerSocket  anyFreePort            System out println  Server serves on port and waiting for a client to communicate                  System in read                System in read               Socket socket   serverSocket accept            System out println  Client request to communicate on port server accepts it              ObjectInputStream in   new ObjectInputStream socket getInputStream             Employee objectReceived    Employee  in readObject            System out println  Server Obj      objectReceived name             socket close            serverSocket close          catch  IOException   ClassNotFoundException e            e printStackTrace                   see   implementing Serializable vs Externalizable

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Serialization is the process of saving an object in a storage medium  such as a file  or a memory buffer  or to transmit it over a network connection  in binary form   The serialized objects are JVM independent and can be re-serialized by any JVM  In this case the  in memory  java objects state are converted into a byte stream  This type of the file can not be understood by the user  It is a special types of object i e  reused by the JVM  Java Virtual Machine   This process of serializing an object is also called deflating or marshalling an object   The object to be serialized must implement java io Serializable Interface   Default serialization mechanism for an object writes the class of the object  the class signature  and the values of all non-transient and non-static fields   class ObjectOutputStream extends java io OutputStream implements ObjectOutput    ObjectOutput interface extends the DataOutput interface and adds methods for serializing objects and writing bytes to the file  The ObjectOutputStream extends java io OutputStream and  implements ObjectOutput  interface  It serializes objects  arrays  and other values to a stream  Thus the constructor of  ObjectOutputStream is written as   ObjectOutput ObjOut   new ObjectOutputStream new FileOutputStream f      Above code has been used to create the instance of the ObjectOutput class with the ObjectOutputStream    constructor which takes the instance of the FileOuputStream as a parameter    The ObjectOutput interface is used by implementing the ObjectOutputStream class  The ObjectOutputStream is constructed to serialize the object    Deserializing an Object in java  The opposite operation of the serialization is called deserialization i e  to extract the data from a series of bytes is s known as deserialization which is also called inflating or unmarshalling   ObjectInputStream extends java io InputStream and  implements ObjectInput  interface  It deserializes objects  arrays  and other values from an input stream  Thus the constructor of  ObjectInputStream is written as   ObjectInputStream obj   new ObjectInputStream new FileInputStream f      Above code of the program creates the instance of the ObjectInputStream class to deserialize that file which had been serialized by the ObjectInputStream class  The above code creates the instance using the instance of the FileInputStream class which holds the specified file object which has to be deserialized because the ObjectInputStream   constructor needs the input stream

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Serialization is the process of converting an object s state to bits so that it can be stored on a hard drive  When you deserialize the same object  it will retain its state later   It lets you recreate objects without having to save the objects  properties by hand   http   en wikipedia org wiki Serialization

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Serialization is taking a  live  object in memory and converting it to a format that can be stored somewhere  eg  in memory  on disk  and later  deserialized  back into a live object

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Return the file as an Object   http   www tutorialspoint com java java serialization htm          import java io             public class SerializeDemo                      public static void main String    args                             Employee e   new Employee                  e name    Reyan Ali                 e address    Phokka Kuan  Ambehta Peer                 e SSN   11122333                e number   101                 try                                  FileOutputStream fileOut                    new FileOutputStream   tmp employee ser                     ObjectOutputStream out   new ObjectOutputStream fileOut                    out writeObject e                    out close                     fileOut close                     System out printf  Serialized data is saved in  tmp employee ser                   catch IOException i                                    i printStackTrace                                                import java io        public class DeserializeDemo              public static void main String    args                     Employee e   null            try                          FileInputStream fileIn   new FileInputStream   tmp employee ser                 ObjectInputStream in   new ObjectInputStream fileIn                e    Employee  in readObject                 in close                 fileIn close               catch IOException i                           i printStackTrace                 return             catch ClassNotFoundException c                           System out println  Employee class not found                 c printStackTrace                 return                        System out println  Deserialized Employee                 System out println  Name      e name             System out println  Address      e address             System out println  SSN      e SSN             System out println  Number      e number

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Serialization is the process of saving an object in a storage medium  such as a file  or a memory buffer  or to transmit it over a network connection  in binary form   The serialized objects are JVM independent and can be re-serialized by any JVM  In this case the  in memory  java objects state are converted into a byte stream  This type of the file can not be understood by the user  It is a special types of object i e  reused by the JVM  Java Virtual Machine   This process of serializing an object is also called deflating or marshalling an object   The object to be serialized must implement java io Serializable Interface   Default serialization mechanism for an object writes the class of the object  the class signature  and the values of all non-transient and non-static fields   class ObjectOutputStream extends java io OutputStream implements ObjectOutput    ObjectOutput interface extends the DataOutput interface and adds methods for serializing objects and writing bytes to the file  The ObjectOutputStream extends java io OutputStream and  implements ObjectOutput  interface  It serializes objects  arrays  and other values to a stream  Thus the constructor of  ObjectOutputStream is written as   ObjectOutput ObjOut   new ObjectOutputStream new FileOutputStream f      Above code has been used to create the instance of the ObjectOutput class with the ObjectOutputStream    constructor which takes the instance of the FileOuputStream as a parameter    The ObjectOutput interface is used by implementing the ObjectOutputStream class  The ObjectOutputStream is constructed to serialize the object    Deserializing an Object in java  The opposite operation of the serialization is called deserialization i e  to extract the data from a series of bytes is s known as deserialization which is also called inflating or unmarshalling   ObjectInputStream extends java io InputStream and  implements ObjectInput  interface  It deserializes objects  arrays  and other values from an input stream  Thus the constructor of  ObjectInputStream is written as   ObjectInputStream obj   new ObjectInputStream new FileInputStream f      Above code of the program creates the instance of the ObjectInputStream class to deserialize that file which had been serialized by the ObjectInputStream class  The above code creates the instance using the instance of the FileInputStream class which holds the specified file object which has to be deserialized because the ObjectInputStream   constructor needs the input stream

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Serialization is taking a  live  object in memory and converting it to a format that can be stored somewhere  eg  in memory  on disk  and later  deserialized  back into a live object

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Daring to answer the 6-year-old question  adding just a very high-level understanding for people new to Java      What is Serialization    Converting an object to bytes     What is Deserialization    Converting bytes back to an object  Deserialization       When is serialization used    When we want to Persist the Object  When we want the object to exist beyond the lifetime of the JVM      Real World Example    ATM  When the account holder tries to withdraw money from the server through ATM  the account holder information like withdrawal details will be serialized and sent to the server where the details are deserialized and used to perform operations      How serialization is performed in java     Implement java io Serializable interface  marker interface so no method to implement   Persist the object  Use java io ObjectOutputStream class  a filter stream which is a wrapper around a lower-level byte stream  to write Object to file systems or transfer a flattened object across a network wire and rebuilt on the other side     writeObject  lt  lt instance gt  gt   - to write an object  readObject    - to read an serialized Object       Remember    When you serialize an object  only the object s state will be saved  not the object s class file or methods   When you serialized a 2-byte object  you see 51 bytes serialized file      Steps how the object is serialized and de-serialized    Answer for   How did it convert to 51 bytes file     First writes the serialization stream magic data  STREAM MAGIC   AC ED   and STREAM VERSION version of the JVM   Then it writes out the metadata of the class associated with an instance  length of the class  the name of the class  serialVersionUID   Then it recursively writes out the metadata of the superclass until it finds java lang Object  Then starts with the actual data associated with the instance  Finally writes the data of objects associated with the instance starting from metadata to the actual content        If you are interested in more in-depth information about Java Serialization please check this link    Edit   One more good link to read   This will answer a few frequent questions    How not to serialize any field in class  Ans  use transient keyword When child class is serialized does parent class get serialized  Ans  No  If a parent is not extending the Serializable interface parents field don t get serialized  When a parent is serialized does child class get serialized  Ans  Yes  by default child class also gets serialized  How to avoid child class from getting serialized  Ans  a  Override writeObject and readObject method and throw NotSerializableException   b  also you can mark all fields transient in child class  Some system-level classes such as Thread  OutputStream  and its subclasses  and Socket are not serializable

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Serialization is the process of converting an object s state to bits so that it can be stored on a hard drive  When you deserialize the same object  it will retain its state later   It lets you recreate objects without having to save the objects  properties by hand   http   en wikipedia org wiki Serialization

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I liked the way  OscarRyz presents  Although here i am continuing the story of serialization which was originally written by  amitgupta   Even though knowing about the robot class structure and having serialized data Earth s scientist were not able to deserialize the data which can make robots working   Exception in thread  main  java io InvalidClassException  SerializeMe  local class incompatible  stream classdesc     Mars s scientists were waiting for the complete payment  Once the payment was done Mars s scientists shared the serialversionUID with Earth s scientists  Earth s scientist set it to robot class and everything became fine

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Serialization is the conversion of an object to a series of bytes  so that the object can be easily saved to persistent storage or streamed across a communication link  The byte stream can then be deserialized - converted into a replica of the original object

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My Two cents from my own blog   Here is a detailed explanation of the Serialization   my own blog   Serialization   Serialization is the process of persisting the state of an object  It is represented and stored in the form of a sequence of bytes  This can be stored in a file  The process to read the state of the object from the file and restoring it is called deserialization   What is the need of Serialization   In modern day architecture  there is always a need to store object state and then retrieve it  For example in Hibernate  to store a object we should make the class Serializable  What it does  is that once the object state is saved in the form of bytes it can be transferred to another system which can then read from the state and retrieve the class  The object state can come from a database or a different jvm or from a separate component  With the help of Serialization we can retrieve the Object state     Code Example and explanation   First let s have a look at the Item Class   public class Item implements Serializable                  This is the Serializable class            private static final long serialVersionUID   475918891428093041L      private Long itemId      private String itemName      private transient Double itemCostPrice      public Item Long itemId  String itemName  Double itemCostPrice            super            this itemId   itemId          this itemName   itemName          this itemCostPrice   itemCostPrice                 public Long getItemId               return itemId                 Override       public String toString               return  Item  itemId     itemId      itemName     itemName      itemCostPrice     itemCostPrice                          public void setItemId Long itemId               this itemId   itemId                   public String getItemName                return itemName                  public void setItemName String itemName                this itemName   itemName                    public Double getItemCostPrice                 return itemCostPrice                     public void setItemCostPrice Double itemCostPrice                 this itemCostPrice   itemCostPrice                In the above code it can be seen that Item class implements Serializable    This is the interface that enables a class to be serializable    Now we can see a variable called serialVersionUID is initialized to Long variable  This number is calculated by the compiler based on the state of the class and the class attributes  This is the number that will help the jvm identify the state of an object when it reads the state of the object from file    For that we can have a look at the official Oracle Documentation      The serialization runtime associates with each serializable class a   version number  called a serialVersionUID  which is used during   deserialization to verify that the sender and receiver of a serialized   object have loaded classes for that object that are compatible with   respect to serialization  If the receiver has loaded a class for the   object that has a different serialVersionUID than that of the   corresponding sender s class  then deserialization will result in an   InvalidClassException  A serializable class can declare its own   serialVersionUID explicitly by declaring a field named    serialVersionUID  that must be static  final  and of type long    ANY-ACCESS-MODIFIER static final long serialVersionUID   42L  If a   serializable class does not explicitly declare a serialVersionUID    then the serialization runtime will calculate a default   serialVersionUID value for that class based on various aspects of the   class  as described in the Java TM  Object Serialization   Specification  However  it is strongly recommended that all   serializable classes explicitly declare serialVersionUID values  since   the default serialVersionUID computation is highly sensitive to class   details that may vary depending on compiler implementations  and can   thus result in unexpected InvalidClassExceptions during   deserialization  Therefore  to guarantee a consistent serialVersionUID   value across different java compiler implementations  a serializable   class must declare an explicit serialVersionUID value  It is also   strongly advised that explicit serialVersionUID declarations use the   private modifier where possible  since such declarations apply only to   the immediately declaring class--serialVersionUID fields are not   useful as inherited members    If you have noticed there is another keyword we have used which is transient   If a field is not serializable  it must be marked transient  Here we marked the itemCostPrice as transient and don t want it to be written in a file  Now let s have a look on how to write the state of an object in the file and then read it from there   public class SerializationExample        public static void main String   args           serialize           deserialize                public static void serialize              Item item   new Item 1L  Pen   12 55            System out println  Before Serialization    item             FileOutputStream fileOut           try                fileOut   new FileOutputStream   tmp item ser                 ObjectOutputStream out   new ObjectOutputStream fileOut                out writeObject item                out close                 fileOut close                 System out println  Serialized data is saved in  tmp item ser                 catch  FileNotFoundException e                       e printStackTrace                 catch  IOException e                       e printStackTrace                              public static void deserialize            Item item           try                   FileInputStream fileIn   new FileInputStream   tmp item ser                    ObjectInputStream in   new ObjectInputStream fileIn                   item    Item  in readObject                    System out println  Serialized data is read from  tmp item ser                    System out println  After Deserialization    item             catch  FileNotFoundException e                    e printStackTrace              catch  IOException e                   e printStackTrace              catch  ClassNotFoundException e                   e printStackTrace                         In the above we can see an example of serialization and deserialization of an object    For that we used two classes  For serializing the object we have used ObjectOutputStream  We have used the method writeObject to write the object in the file    For Deserializing we have used ObjectInputStream which reads from the object from the file  It uses readObject to read the object data from the file    The output of the above code would be like   Before SerializationItem  itemId 1  itemName Pen  itemCostPrice 12 55  Serialized data is saved in  tmp item ser After DeserializationItem  itemId 1  itemName Pen  itemCostPrice null    Notice that itemCostPrice from deserialized object is null as it was not written   We have already discussed the basics of Java Serialization in part I of this article    Now let s discuss it deeply and how it works   First let s start with the serialversionuid   The serialVersionUID is used as a version control in a Serializable class    If you do not explicitly declare a serialVersionUID  JVM will do it for you automatically  based on various properties of the Serializable class    Java s Algorithm of Calculating serialversionuid  Read more details here         The class name            The class modifiers written as a 32-bit integer    The name of each interface sorted by name    For each field of the class sorted by field name  except private static and private transient fields    The name of the field    The   modifiers of the field written as a 32-bit integer    The descriptor   of the field      If a class initializer exists  write out the following  The name of the method      The modifier of the method  java lang reflect Modifier STATIC  written as a 32-bit integer    The descriptor of the method    V    For each non-private constructor sorted by method name and signature    The name of the method      The modifiers of the   method written as a 32-bit integer    The descriptor of the method      For each non-private method sorted by method name and signature    The name of the method    The modifiers of the method written as a   32-bit integer    The descriptor of the method    The SHA-1 algorithm is executed on the stream of bytes produced by DataOutputStream and produces five 32-bit values sha 0  4   The   hash value is assembled from the first and second 32-bit values of the   SHA-1 message digest  If the result of the message digest  the five   32-bit words H0 H1 H2 H3 H4  is in an array of five int values named   sha  the hash value would be computed as follows              long hash     sha 0   gt  gt  gt  24   amp  0xFF     gt               sha 0   gt  gt  gt  16   amp  0xFF   lt  lt  8    gt               sha 0   gt  gt  gt  8   amp  0xFF   lt  lt  16    gt               sha 0   gt  gt  gt  0   amp  0xFF   lt  lt  24    gt               sha 1   gt  gt  gt  24   amp  0xFF   lt  lt  32    gt               sha 1   gt  gt  gt  16   amp  0xFF   lt  lt  40    gt               sha 1   gt  gt  gt  8   amp  0xFF   lt  lt  48    gt           sha 1   gt  gt  gt  0   amp  0xFF   lt  lt  56    Java s serialization algorithm     The algorithm to serialize an object is described as below    1  It writes out the metadata of the class associated with an instance    2  It recursively writes out the description of the superclass until it finds java lang object    3  Once it finishes writing the metadata information  it then starts with the actual data associated with the instance  But this time  it   starts from the topmost superclass    4  It recursively writes the data associated with the instance  starting from the least superclass to the most-derived class    Things To Keep In Mind    Static fields in a class cannot be serialized    public class A implements Serializable       String s       static String staticString    I won t be serializable      If the serialversionuid is different in the read class it will throw a InvalidClassException exception    If a class implements serializable then all its sub classes will also be serializable     public class A implements Serializable          public class B extends A        also Serializable  If a class has a reference of another class  all the references must be Serializable otherwise serialization process will not be performed  In such case  NotSerializableException is thrown at runtime    Eg   public class B       String s       A a     class A needs to be serializable i e  it must implement Serializable

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My Two cents from my own blog   Here is a detailed explanation of the Serialization   my own blog   Serialization   Serialization is the process of persisting the state of an object  It is represented and stored in the form of a sequence of bytes  This can be stored in a file  The process to read the state of the object from the file and restoring it is called deserialization   What is the need of Serialization   In modern day architecture  there is always a need to store object state and then retrieve it  For example in Hibernate  to store a object we should make the class Serializable  What it does  is that once the object state is saved in the form of bytes it can be transferred to another system which can then read from the state and retrieve the class  The object state can come from a database or a different jvm or from a separate component  With the help of Serialization we can retrieve the Object state     Code Example and explanation   First let s have a look at the Item Class   public class Item implements Serializable                  This is the Serializable class            private static final long serialVersionUID   475918891428093041L      private Long itemId      private String itemName      private transient Double itemCostPrice      public Item Long itemId  String itemName  Double itemCostPrice            super            this itemId   itemId          this itemName   itemName          this itemCostPrice   itemCostPrice                 public Long getItemId               return itemId                 Override       public String toString               return  Item  itemId     itemId      itemName     itemName      itemCostPrice     itemCostPrice                          public void setItemId Long itemId               this itemId   itemId                   public String getItemName                return itemName                  public void setItemName String itemName                this itemName   itemName                    public Double getItemCostPrice                 return itemCostPrice                     public void setItemCostPrice Double itemCostPrice                 this itemCostPrice   itemCostPrice                In the above code it can be seen that Item class implements Serializable    This is the interface that enables a class to be serializable    Now we can see a variable called serialVersionUID is initialized to Long variable  This number is calculated by the compiler based on the state of the class and the class attributes  This is the number that will help the jvm identify the state of an object when it reads the state of the object from file    For that we can have a look at the official Oracle Documentation      The serialization runtime associates with each serializable class a   version number  called a serialVersionUID  which is used during   deserialization to verify that the sender and receiver of a serialized   object have loaded classes for that object that are compatible with   respect to serialization  If the receiver has loaded a class for the   object that has a different serialVersionUID than that of the   corresponding sender s class  then deserialization will result in an   InvalidClassException  A serializable class can declare its own   serialVersionUID explicitly by declaring a field named    serialVersionUID  that must be static  final  and of type long    ANY-ACCESS-MODIFIER static final long serialVersionUID   42L  If a   serializable class does not explicitly declare a serialVersionUID    then the serialization runtime will calculate a default   serialVersionUID value for that class based on various aspects of the   class  as described in the Java TM  Object Serialization   Specification  However  it is strongly recommended that all   serializable classes explicitly declare serialVersionUID values  since   the default serialVersionUID computation is highly sensitive to class   details that may vary depending on compiler implementations  and can   thus result in unexpected InvalidClassExceptions during   deserialization  Therefore  to guarantee a consistent serialVersionUID   value across different java compiler implementations  a serializable   class must declare an explicit serialVersionUID value  It is also   strongly advised that explicit serialVersionUID declarations use the   private modifier where possible  since such declarations apply only to   the immediately declaring class--serialVersionUID fields are not   useful as inherited members    If you have noticed there is another keyword we have used which is transient   If a field is not serializable  it must be marked transient  Here we marked the itemCostPrice as transient and don t want it to be written in a file  Now let s have a look on how to write the state of an object in the file and then read it from there   public class SerializationExample        public static void main String   args           serialize           deserialize                public static void serialize              Item item   new Item 1L  Pen   12 55            System out println  Before Serialization    item             FileOutputStream fileOut           try                fileOut   new FileOutputStream   tmp item ser                 ObjectOutputStream out   new ObjectOutputStream fileOut                out writeObject item                out close                 fileOut close                 System out println  Serialized data is saved in  tmp item ser                 catch  FileNotFoundException e                       e printStackTrace                 catch  IOException e                       e printStackTrace                              public static void deserialize            Item item           try                   FileInputStream fileIn   new FileInputStream   tmp item ser                    ObjectInputStream in   new ObjectInputStream fileIn                   item    Item  in readObject                    System out println  Serialized data is read from  tmp item ser                    System out println  After Deserialization    item             catch  FileNotFoundException e                    e printStackTrace              catch  IOException e                   e printStackTrace              catch  ClassNotFoundException e                   e printStackTrace                         In the above we can see an example of serialization and deserialization of an object    For that we used two classes  For serializing the object we have used ObjectOutputStream  We have used the method writeObject to write the object in the file    For Deserializing we have used ObjectInputStream which reads from the object from the file  It uses readObject to read the object data from the file    The output of the above code would be like   Before SerializationItem  itemId 1  itemName Pen  itemCostPrice 12 55  Serialized data is saved in  tmp item ser After DeserializationItem  itemId 1  itemName Pen  itemCostPrice null    Notice that itemCostPrice from deserialized object is null as it was not written   We have already discussed the basics of Java Serialization in part I of this article    Now let s discuss it deeply and how it works   First let s start with the serialversionuid   The serialVersionUID is used as a version control in a Serializable class    If you do not explicitly declare a serialVersionUID  JVM will do it for you automatically  based on various properties of the Serializable class    Java s Algorithm of Calculating serialversionuid  Read more details here         The class name            The class modifiers written as a 32-bit integer    The name of each interface sorted by name    For each field of the class sorted by field name  except private static and private transient fields    The name of the field    The   modifiers of the field written as a 32-bit integer    The descriptor   of the field      If a class initializer exists  write out the following  The name of the method      The modifier of the method  java lang reflect Modifier STATIC  written as a 32-bit integer    The descriptor of the method    V    For each non-private constructor sorted by method name and signature    The name of the method      The modifiers of the   method written as a 32-bit integer    The descriptor of the method      For each non-private method sorted by method name and signature    The name of the method    The modifiers of the method written as a   32-bit integer    The descriptor of the method    The SHA-1 algorithm is executed on the stream of bytes produced by DataOutputStream and produces five 32-bit values sha 0  4   The   hash value is assembled from the first and second 32-bit values of the   SHA-1 message digest  If the result of the message digest  the five   32-bit words H0 H1 H2 H3 H4  is in an array of five int values named   sha  the hash value would be computed as follows              long hash     sha 0   gt  gt  gt  24   amp  0xFF     gt               sha 0   gt  gt  gt  16   amp  0xFF   lt  lt  8    gt               sha 0   gt  gt  gt  8   amp  0xFF   lt  lt  16    gt               sha 0   gt  gt  gt  0   amp  0xFF   lt  lt  24    gt               sha 1   gt  gt  gt  24   amp  0xFF   lt  lt  32    gt               sha 1   gt  gt  gt  16   amp  0xFF   lt  lt  40    gt               sha 1   gt  gt  gt  8   amp  0xFF   lt  lt  48    gt           sha 1   gt  gt  gt  0   amp  0xFF   lt  lt  56    Java s serialization algorithm     The algorithm to serialize an object is described as below    1  It writes out the metadata of the class associated with an instance    2  It recursively writes out the description of the superclass until it finds java lang object    3  Once it finishes writing the metadata information  it then starts with the actual data associated with the instance  But this time  it   starts from the topmost superclass    4  It recursively writes the data associated with the instance  starting from the least superclass to the most-derived class    Things To Keep In Mind    Static fields in a class cannot be serialized    public class A implements Serializable       String s       static String staticString    I won t be serializable      If the serialversionuid is different in the read class it will throw a InvalidClassException exception    If a class implements serializable then all its sub classes will also be serializable     public class A implements Serializable          public class B extends A        also Serializable  If a class has a reference of another class  all the references must be Serializable otherwise serialization process will not be performed  In such case  NotSerializableException is thrown at runtime    Eg   public class B       String s       A a     class A needs to be serializable i e  it must implement Serializable

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You can think of serialization as the process of converting an object instance into a sequence of bytes  which may be binary or not depending on the implementation    It is very useful when you want to transmit one object data across the network  for instance from one JVM to another   In Java  the serialization mechanism is built into the platform  but you need to implement the Serializable interface to make an object serializable   You can also prevent some data in your object from being serialized by marking the attribute as transient   Finally you can override the default mechanism  and provide your own  this may be suitable in some special cases  To do this  you use one of the hidden features in java   It is important to notice that what gets serialized is the  value  of the object  or the contents  and not the class definition  Thus methods are not serialized   Here is a very basic sample with comments to facilitate its reading   import java io    import java util        This class implements  Serializable  to let the system know    it s ok to do it  You as programmer are aware of that  public class SerializationSample implements Serializable           These attributes conform the  value  of the object          These two will be serialized      private String aString    The value of that string       private int    someInteger   0          But this won t since it is marked as transient      private transient List lt File gt  unInterestingLongLongList          Main method to test      public static void main  String    args   throws IOException                 Create a sample object  that contains the default values          SerializationSample instance   new SerializationSample                The  ObjectOutputStream  class has the default             definition to serialize an object          ObjectOutputStream oos   new ObjectOutputStream                                     By using  FileOutputStream  we will                                    Write it to a File in the file system                                   It could have been a Socket to another                                    machine  a database  an in memory array  etc                                 new FileOutputStream new File  o ser                  do the magic           oos writeObject  instance               close the writing          oos close              When we run this program  the file  o ser  is created and we can see what happened behind   If we change the value of  someInteger to  for example Integer MAX VALUE  we may compare the output to see what the difference is   Here s a screenshot showing precisely that difference     Can you spot the differences      There is an additional relevant field in Java serialization  The serialversionUID but I guess this is already too long to cover it

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I liked the way  OscarRyz presents  Although here i am continuing the story of serialization which was originally written by  amitgupta   Even though knowing about the robot class structure and having serialized data Earth s scientist were not able to deserialize the data which can make robots working   Exception in thread  main  java io InvalidClassException  SerializeMe  local class incompatible  stream classdesc     Mars s scientists were waiting for the complete payment  Once the payment was done Mars s scientists shared the serialversionUID with Earth s scientists  Earth s scientist set it to robot class and everything became fine

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Serialization is the conversion of an object to a series of bytes  so that the object can be easily saved to persistent storage or streamed across a communication link  The byte stream can then be deserialized - converted into a replica of the original object

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Java Object Serialization    Serialization is a mechanism to transform a graph of Java objects into an array of bytes for storage to disk file  or transmission across a network   then by using deserialization we can restore the graph of objects  Graphs of objects are restored correctly using a reference sharing mechanism  But before storing  check whether serialVersionUID from input-file network and  class file serialVersionUID are the same  If not  throw a java io InvalidClassException      Each versioned class must identify the original class version for which it is capable of writing streams and from which it can read  For example  a versioned class must declare       serialVersionUID Syntax     ANY-ACCESS-MODIFIER static final long serialVersionUID    64-bit has L  private static final long serialVersionUID   3487495895819393L       serialVersionUID is essential to the serialization process  But it is optional for the developer to add it into the java source file  If a serialVersionUID is not included  the serialization runtime will generate a serialVersionUID and associate it with the class  The serialized object will contain this serialVersionUID along with other data   Note - It is strongly recommended that all serializable classes explicitly declare a serialVersionUID  since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations  and can thus result in unexpected serialVersionUID conflicts during deserialization  causing deserialization to fail   Inspecting Serializable Classes         A Java object is only serializable  if a class or any of its superclasses implements either the java io Serializable interface     or its subinterface  java io Externalizable     A class must implement java io Serializable interface in order to serialize its object successfully  Serializable is a marker interface and used to inform the compiler that the class implementing it has to be added serializable behavior  Here Java Virtual Machine  JVM  is responsible for its automatic serialization      transient Keyword  java io Serializable interface      While serializing an object  if we don t want certain data members of the object to be serialized we can use the transient modifier  The transient keyword will prevent that data member from being serialized          Fields declared as transient or static are ignored by the serialization process               TRANSIENT  amp  VOLATILE      -------------- -------- -------------------------------------     Flag Name      Value   Interpretation                         -------------- -------- -------------------------------------    ACC VOLATILE   0x0040   Declared volatile  cannot be cached    -------------- -------- -------------------------------------   ACC TRANSIENT   0x0080   Declared transient  not written or                              read by a persistent object manager    -------------- -------- -------------------------------------       class Employee implements Serializable       private static final long serialVersionUID   2L      static int id       int eno       String name      transient String password     Using transient keyword means its not going to be Serialized       Implementing the Externalizable interface allows the object to assume complete control over the contents and format of the object s serialized form  The methods of the Externalizable interface  writeExternal and readExternal  are called to save and restore the objects state  When implemented by a class they can write and read their own state using all of the methods of ObjectOutput and ObjectInput  It is the responsibility of the objects to handle any versioning that occurs      class Emp implements Externalizable       int eno       String name      transient String password     No use of transient  we need to take care of write and read        Override     public void writeExternal ObjectOutput out  throws IOException           out writeInt eno           out writeUTF name             out writeUTF password              Override     public void readExternal ObjectInput in  throws IOException  ClassNotFoundException           this eno   in readInt            this name   in readUTF              this password   in readUTF       java io EOFException            Only objects that support the java io Serializable or java io Externalizable interface can be written to read from streams  The class of each serializable object is encoded including the class name and signature of the class  the values of the object s fields and arrays  and the closure of any other objects referenced from the initial objects     Serializable Example For Files    public class SerializationDemo       static String fileName    D  serializable file ser        public static void main String   args  throws IOException  ClassNotFoundException  InstantiationException  IllegalAccessException           Employee emp   new Employee             Employee id   1     Can not Serialize Class data          emp eno   77          emp name    Yash           emp password    confidential           objects WriteRead emp  fileName            Emp e   new Emp             e eno   77          e name    Yash           e password    confidential           objects WriteRead External e  fileName              String stubHost    127 0 0 1           Integer anyFreePort   7777          socketRead anyFreePort     Thread1         socketWrite emp  stubHost  anyFreePort     Thread2              public static void objects WriteRead  Employee obj  String serFilename   throws IOException          FileOutputStream fos   new FileOutputStream  new File  serFilename              ObjectOutputStream objectOut   new ObjectOutputStream  fos            objectOut writeObject  obj            objectOut close            fos close             System out println  Data Stored in to a file             try               FileInputStream fis   new FileInputStream  new File  serFilename                  ObjectInputStream ois   new ObjectInputStream  fis                Object readObject              readObject   ois readObject                String calssName   readObject getClass   getName                System out println  Restoring Class Name      calssName      InvalidClassException              Employee emp    Employee  readObject              System out format  Obj No  s  Name  s  Pass  s    emp eno  emp name  emp password                ois close              catch  ClassNotFoundException e                e printStackTrace                        public static void objects WriteRead External  Emp obj  String serFilename   throws IOException           FileOutputStream fos   new FileOutputStream new File  serFilename             ObjectOutputStream objectOut   new ObjectOutputStream  fos             obj writeExternal  objectOut            objectOut flush             fos close             System out println  Data Stored in to a file             try                  create a new instance and read the assign the contents from stream              Emp emp   new Emp                 FileInputStream fis   new FileInputStream new File  serFilename                 ObjectInputStream ois   new ObjectInputStream  fis                 emp readExternal ois                System out format  Obj No  s  Name  s  Pass  s    emp eno  emp name  emp password                ois close              catch  ClassNotFoundException e                e printStackTrace                          Serializable Example Over Network  Distributing object s state across different address spaces  either in different processes on the same computer  or even in multiple computers connected via a network  but which work together by sharing data and invoking methods     Data Marshalling Stubs and Skeletons            Creates a stream socket and connects it to the specified port number on the named host       public static void socketWrite Employee objectToSend  String stubHost  Integer anyFreePort        try      CLIENT - Stub marshalling          Socket client   new Socket stubHost  anyFreePort           ObjectOutputStream out   new ObjectOutputStream client getOutputStream             out writeObject objectToSend           out flush            client close          catch  IOException e            e printStackTrace               Creates a server socket  bound to the specified port   public static void socketRead   Integer anyFreePort         try      SERVER - Stub unmarshalling           ServerSocket serverSocket   new ServerSocket  anyFreePort            System out println  Server serves on port and waiting for a client to communicate                  System in read                System in read               Socket socket   serverSocket accept            System out println  Client request to communicate on port server accepts it              ObjectInputStream in   new ObjectInputStream socket getInputStream             Employee objectReceived    Employee  in readObject            System out println  Server Obj      objectReceived name             socket close            serverSocket close          catch  IOException   ClassNotFoundException e            e printStackTrace                   see   implementing Serializable vs Externalizable

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I ll offer an analogy to potentially assist in solidifying the conceptual purpose practicality of object serialization deserialization   I imagine object serialization deserialization in the context of attempting to move an object through a storm drain  The object is essentially  decomposed  or serialized into more modular versions of itself - in this case  a series of bytes - in order to effectively be granted passage through a medium  In a computational sense  we could view the path traveled by the bytes through the storm drain as being akin to bytes traveling through a network  We re transmuting our object in order to conform to a more desirable mode of transportation  or format  The serialized object will typically be stored in a binary file which may later be read from  written to  or both   Perhaps once our object is able to slip through the drain as a decomposed series of bytes  we may wish to store that representation of the object as binary data within a database or hard disk drive  The main takeaway though  is that with serialization deserialization  we have the option to let our object remain in it s binary form after being serialized  or  retrieve  the object s original form by performing deserialization

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Serialization is the process of converting an object s state to bits so that it can be stored on a hard drive  When you deserialize the same object  it will retain its state later   It lets you recreate objects without having to save the objects  properties by hand   http   en wikipedia org wiki Serialization

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Daring to answer the 6-year-old question  adding just a very high-level understanding for people new to Java      What is Serialization    Converting an object to bytes     What is Deserialization    Converting bytes back to an object  Deserialization       When is serialization used    When we want to Persist the Object  When we want the object to exist beyond the lifetime of the JVM      Real World Example    ATM  When the account holder tries to withdraw money from the server through ATM  the account holder information like withdrawal details will be serialized and sent to the server where the details are deserialized and used to perform operations      How serialization is performed in java     Implement java io Serializable interface  marker interface so no method to implement   Persist the object  Use java io ObjectOutputStream class  a filter stream which is a wrapper around a lower-level byte stream  to write Object to file systems or transfer a flattened object across a network wire and rebuilt on the other side     writeObject  lt  lt instance gt  gt   - to write an object  readObject    - to read an serialized Object       Remember    When you serialize an object  only the object s state will be saved  not the object s class file or methods   When you serialized a 2-byte object  you see 51 bytes serialized file      Steps how the object is serialized and de-serialized    Answer for   How did it convert to 51 bytes file     First writes the serialization stream magic data  STREAM MAGIC   AC ED   and STREAM VERSION version of the JVM   Then it writes out the metadata of the class associated with an instance  length of the class  the name of the class  serialVersionUID   Then it recursively writes out the metadata of the superclass until it finds java lang Object  Then starts with the actual data associated with the instance  Finally writes the data of objects associated with the instance starting from metadata to the actual content        If you are interested in more in-depth information about Java Serialization please check this link    Edit   One more good link to read   This will answer a few frequent questions    How not to serialize any field in class  Ans  use transient keyword When child class is serialized does parent class get serialized  Ans  No  If a parent is not extending the Serializable interface parents field don t get serialized  When a parent is serialized does child class get serialized  Ans  Yes  by default child class also gets serialized  How to avoid child class from getting serialized  Ans  a  Override writeObject and readObject method and throw NotSerializableException   b  also you can mark all fields transient in child class  Some system-level classes such as Thread  OutputStream  and its subclasses  and Socket are not serializable

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Serialization is taking a  live  object in memory and converting it to a format that can be stored somewhere  eg  in memory  on disk  and later  deserialized  back into a live object

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Serialization is the process of turning a Java object into byte array and then back into object again with its preserved state. Useful for various things like sending objects over network or caching things to disk.

Read more from this short article which explains programming part of the process quite well and then move over to to Serializable javadoc. You may also be interested in reading this related question.

[java] What is object serialization?

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Examples related to serialization

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