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Chapter 12, Serialization

1. Chapter 12, Serialization
2. Byte streams
3. Serializable
4. class SavePerson
5. class RestorePerson
6. Further Reading

1. Chapter 12, Serialization

• Once object is created, data attributes occupy memory that belongs to the object.

• Objects are always in some kind of state.

• When the application terminates, objects are destroyed and memory is freed.

• However, state of each object can be preserved on a permanent media.

• Objects that are preserved in this way are called persistent objects.

2. Byte streams

• Serialization is the process of writing the state of an object to a byte stream.

• Byte stream is simply a memory buffer provided to us by the system environment.

• Byte stream is very easy to store in a file and restore from the file afterwards.

• Restoring object state from a byte stream is called deserialization.

• Serialization can be complex when an object has references to other objects;

  • in such case writing and restoring state of all objects needs to be

    • properly ordered

    • arranged to restore both the objects and the references to them.

3. Serializable

• Only object that implements Serializable interface can be saved and restored by the serialization facilities.

• Serializable interface defines no operations.

• Why? Because the Serializable interface only indicates that a class may be serialized.

  
      import java.util.*;
      import java.io.*;
  
      class Person implements Serializable{
          private String name;
  
          public Person() {
          }
  
          public Person( String n ){
              System.out.println("In Person ctr");
              name = n;
          }
  
          String getName() {
              return name;
          }
      }
  
  

4. class SavePerson

• 
      import java.util.*;
      import java.io.*;
  
      public class SavePerson {
          public static void main(String args[]){
              Person person = new Person( "Jack Jones" );
  
              try {
                  FileOutputStream fos = new FileOutputStream( "Name.txt" );
                  ObjectOutputStream oos = new ObjectOutputStream( fos );
                  System.out.print( "Person Name Written: " );
                  System.out.println( person.getName() );
  
                  oos.writeObject( person );
                  oos.flush();
                  oos.close();
  
              } catch(Exception e){
                  e.printStackTrace();
              }
          }
      }
  
  

5. class RestorePerson

• 
      import java.io.*;
      import java.util.*;
  
      public class RestorePerson{
          public static void main( String args[] ) {
              try{
                  FileInputStream fis = new FileInputStream( "Name.txt" );
                  ObjectInputStream ois = new ObjectInputStream( fis );
                  Person person = ( Person ) ois.readObject();
                  System.out.print( "Person Name Restored: " );
                  System.out.println( person.getName() );
                  ois.close();
              } catch ( Exception e ) {
                  e.printStackTrace();
              }
          }
      }
  
  

6. Further Reading

This week's study guide

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