What is a marker interface?

Question

How is it different from a normal interface?

Answer 1

These interfaces do not declare any methods that are needed to be declared by a generic interface. These only indicate the compatibility with specific operations. Some examples of these interfaces are as follows:

• java.io.Serializable
• Cloneable

Yes, these interfaces do not contain any methods but these are required to be implemented by a class in order for the class to be serialized or deserialized. If you're looking to learn java to understand the core of it, interfaces are one of the fundamental building blocks for that.