What are Marker Interfaces in Java

In Java, a marker interface is an interface with no methods or fields. It is used to mark a class that has some special behavior or property. By implementing a marker interface, a class indicates to the compiler or runtime environment that it has a certain behavior or property.

One example of a marker interface in Java is the Serializable interface. A class that implements the Serializable interface indicates to the runtime environment that its instances can be serialized and deserialized, which means they can be converted to and from a stream of bytes. When an object is serialized, its state is converted to a stream of bytes, which can then be stored in a file or transmitted over a network. When an object is deserialized, the byte stream is converted back into an object with the same state as the original object. Here is an example of a class that implements the Serializable interface:

import java.io.Serializable;

public class Employee implements Serializable {
    private int id;
    private String name;
    private double salary;

    // constructors, getters, setters, and other methods go here
}

Another example of a marker interface in Java is the Cloneable interface. A class that implements the Cloneable interface indicates to the runtime environment that its instances can be cloned, which means they can be copied using the Object.clone() method. Here is an example of a class that implements the Cloneable interface:

public class Employee implements Cloneable {
    private int id;
    private String name;
    private double salary;

    // constructors, getters, setters, and other methods go here

    @Override
    public Employee clone() throws CloneNotSupportedException {
        return (Employee) super.clone();
    }
}

Note that the clone() method must be overridden in a class that implements the Cloneable interface, and it must throw a CloneNotSupportedException if the object cannot be cloned.

Marker interfaces are generally used as a way to provide a mechanism for adding metadata to classes. They allow developers to write code that can take advantage of certain behavior or properties of a class without requiring the class to implement any specific methods or fields.