Can you explain what the Serializable interface in Java means and what it is used for?

In Java, the Serializable interface is used to indicate that an object of a class can be serialized — that is, converted into a byte stream for storage or transmission.

This is used, for example, for:

• Saving the state of an object to disk.
• Transmitting an object over a network.
• Caching objects.

The interface does not contain any methods; it is a marker interface. To make a class serializable, it is enough to implement Serializable:

import java.io.Serializable;

public class User implements Serializable {
    private String name;
    private int age;
    // getters, setters, constructors
}

During serialization, the JVM automatically saves the state of all fields of the object, except those declared as transient.