Home > Data Structures and Algorithms Questions >Define Externalizable Interface and itspurpose with examples.
Externalization serves the purpose of custom Serialization, where we can decide what to store in stream.
Externalizable interface present in java.io, is used for Externalization which extends Serializable interface. It consist of two methods which we have to override to write/read object into/from stream which are-
// to read object from stream
void readExternal(ObjectInput in)
// to write object into stream
void writeExternal(ObjectOutput out)
import java.io.*;
class Car implements Externalizable {
static int age;
String name;
int year;
public Car()
{
System.out.println("Default Constructor called");
}
Car(String n, int y)
{
this.name = n;
this.year = y;
age = 10;
}
public void writeExternal(ObjectOutput out)
throws IOException
{
out.writeObject(name);
out.writeInt(age);
out.writeInt(year);
}
public void readExternal(ObjectInput in)
throws IOException, ClassNotFoundException
{
name = (String)in.readObject();
year = in.readInt();
age = in.readInt();
}
public String toString()
{
return ("Name: " + name + "\n" +
"Year: " + year + "\n" +
"Age: " + age);
}
}
public class ExternExample {
public static void main(String[] args)
{
Car car = new Car("Shubham", 1995);
Car newcar = null;
// Serialize the car
try {
FileOutputStream fo = new FileOutputStream("gfg.txt");
ObjectOutputStream so = new ObjectOutputStream(fo);
so.writeObject(car);
so.flush();
}
catch (Exception e) {
System.out.println(e);
}
// Deserializa the car
try {
FileInputStream fi = new FileInputStream("gfg.txt");
ObjectInputStream si = new ObjectInputStream(fi);
newcar = (Car)si.readObject();
}
catch (Exception e) {
System.out.println(e);
}
System.out.println("The original car is:\n" + car);
System.out.println("The new car is:\n" + newcar);
}
}