Posted in: Companies interview questions,Core Java,Serialization
What is Serialization ?
Object serialization is the process of saving an object's state to a sequence of bytes, as well as the process of rebuilding those bytes into a live object at some future time. The Java Serialization API provides a standard mechanism for developers to handle object serialization.- Allows the persistent storage of objects
- Uses the java.io.Serializable interface
- ObjectInputStream and ObjectOutputStream
- Allows you to save objects to file and load them at a later date
- Really should only be used for temporary storage of objects
What is actually saved?
- Only class name and object’s data is saved
- If that data is an object, it is also saved
- Each object is given a serial number
- If an object has already been saved (e.g. within a graph) then only the serial number is saved
- Methods are not saved
- Static information not saved
Making an object serializable :
- Implement the Serializable interface
- Does not require any methods to be implemented
- Implement the Externalizable interface
- default behaviour only saves class name
- must implement readExternal and writeExternal
To save and load an Object:
To save the objects to file:
FileOutputStream file = new FileOutputStream("data.ser");
ObjectOutputStream output = new ObjectOutputStream(file);
output.writeObject(family);
output.close();
ObjectOutputStream output = new ObjectOutputStream(file);
output.writeObject(family);
output.close();
To load the objects from file:
FileInputStream file = new FileInputStream("data.ser");
ObjectInputStream input = new ObjectInputStream(file);
Family family = (Family) input.readObject();
input.close();
ObjectInputStream input = new ObjectInputStream(file);
Family family = (Family) input.readObject();
input.close();