Java - Marker Interface

Interface with no fields or methods i.e. empty interface. Examples of marker interface are Serializable, Cloneable and Remote interface. All these interfaces are empty interfaces.

public interface Cloneable{
//nothing here
}        

Cloneable interface

• Present in java.lang package
• There is a clone() method in the Object class and any class that implements Cloneable Interface can use the clone() method to make field-for-field copy of instances of that class.
• Invoking Object’s clone method on an instance of the class that does not implement the Cloneable interface results in an exception CloneNotSupportedException being thrown. By convention, classes that implement this interface should override Object.clone() method.

package oopsconcept;

public class Car implements Cloneable {
	String carName;
	int mileage;
   // constructor of car class
	public Car(String name, int mil) {
		this.carName = name;
		this.mileage = mil;
	}

	// Overriding clone() method by simply calling Object class clone() method.
	protected Object clone() throws CloneNotSupportedException {
		return super.clone();
	}

	public static void main(String[] args) throws CloneNotSupportedException {
		Car c = new Car("Honda Amaze", 25);
		// cloning 'c' and holding new cloned object reference in d
		// down-casting as clone() return type is Object

		Car d = (Car) c.clone();
		System.out.println(d.carName);
		System.out.println(d.mileage);
	}
}        

Output:
Honda Amaze
25        

Serializable interface :

• Present in java.io package.
• It is used to make an object eligible for saving its state into a file which is called Serialization.
• Classes that do not implement this interface will not have any of their state serialized or deserialized. All subtypes of a serializable class are themselves serializable.

package oopsconcept;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class CarSerializable implements Serializable {
	String carName;
	int mileage;

	// constructor of car class
	public CarSerializable(String name, int mil) {
		this.carName = name;
		this.mileage = mil;
	}

	public static void main(String[] args) throws IOException, ClassNotFoundException {

		CarSerializable c = new CarSerializable("Honda Amaze", 25);

		// Serilaizing 'c'
		File file = new File("person.txt");
		FileOutputStream fo = new FileOutputStream(file);

		ObjectOutputStream ob = new ObjectOutputStream(fo);
		ob.writeObject(c);
		System.out.println("File path: " + file.getAbsolutePath());
		// Deserializing 'c'
		FileInputStream fi = new FileInputStream("file.txt");
		ObjectInput ob1 = new ObjectInputStream(fi);
		// down-casting object
		CarSerializable d = (CarSerializable) ob1.readObject();

		System.out.println(d.carName + ":" + d.mileage);

		// Close the streams
		ob.close();
		ob1.close();

	}}        

Output:
File path: D:\Selenium\Java Interview Question\person.txt
Honda Amaze:25        

Remote interface :

• Present in java.rmi package
• A remote object is an object which is stored at one machine and accessed from another machine. So, to make an object a remote object, we need to flag it with Remote interface. Here, Remote interface serves to identify interfaces whose methods may be invoked from a non-local virtual machine.Any object that is a remote object must directly or indirectly implement this interface.
• RMI (Remote Method Invocation) provides some convenience classes that remote object implementations can extend which facilitate remote object creation.