Can you give an example of an interface used only as a marker or label without methods?

In Java, an interface that is used only as a marker or label is called a marker interface. It does not contain methods and serves to indicate a certain property or behavior of a class.

An example of such an interface is java.io.Serializable. A class implementing this interface signals that its objects can be serialized, although the interface itself does not contain any methods:

public interface Serializable {
    // No methods
}

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

Here, Serializable is a marker used by the JVM and libraries to determine if an object can be serialized.