Serialization

The process of saving and object to a file is called Serialization. Strictly Serialization means the process of converting java supported format object to network supported format object OR Process of converting object into stream of bytes.

            If a variable is declared as transient at the time to serialization JVM ignores the value of that transient variable. Instead of original value JVM saves default value. Hence transient means not to serialize.

Example: while saving Account information permanently to a file, we are not allowed to save password for security reasons, such type of variables we have to declare by transient keyword.

We can serialize only serializable objects violation leads to RuntimeException saying “NotSerializableException”. An Object is said to be seriablizable if and only if the corresponding class implements serializable interface.

           

Import java.io.*;

            public class TransientDemo implements Serializable{

                        int i=10;

                        int j=20;

                       

                        public static void main(String args[]) throws Exception{

                                    TransientDemo t1 = new TransientDemo();

                                    System.out.println(t1.i + "----------" + t1.j);

                                   

                                    //Serialization Process

                                    FileOutputStream fos = new FileOutputStream("abc.txt");

                                    ObjectOutputStream oos = new ObjectOutputStream(fos);

                                    oos.writeObject(t1);

                                   

                                    //De-serialization Process

                                    FileInputStream fis = new FileInputStream("abc.txt");

                                    ObjectInputStream ois = new ObjectInputStream(fis);

                                    ois.readObject();

                                   

                                    TransientDemo t2 = (TransientDemo) ois.readObject();

                                    System.out.println(t2.i + "--------" + t2.j);

                        }

            }

            Output: 10----------20

                         10----------20

Case 1: If we won’t implement serializable interface we get RunTimeException java.io.NonSerializableException.

Case 2: If we won’t place “throws Exception” at method we get compile time exception saying unreported exception must be caught or declared to be throws.

Case 3: We should type cast readObject else we get error Incompatable type error.

Analysis:

Case 1:

            int i = 10;

            int j = 20; output: 10----20

                                       10----20

Case 2:                       

            int i = 10;

            transient int j = 20; output: 10----20

                                                      10----0

Case 3:

            transient static int i=10;

            int j=20; output: 10----20

                                       10----20

Transient is useless in case of static variable.

Static variables never part of object state. Hence they are not participating in serialization process. Declaring a static variable as transient is useless & there is not impact

Case 4:

            transient final int i=10;

            int j=20; output: 10----20

                                       10----20

Declaring a final variable as transient is useless and there is no impact.