Complete Java SE 8 Developer Bootcamp - Marker and Functional Interfaces

The video tutorial covers two types of interfaces in Java: marker interfaces and functional interfaces. Marker interfaces, like Serializable, have no methods and are used to indicate certain properties of a class. Functional interfaces have one abstract method and are linked to lambda expressions introduced in Java 8. The tutorial explains the purpose and usage of these interfaces, including the Serializable interface's role in object serialization and the concept of transient fields.

Define a functional interface and explain its characteristics.

What is the significance of the one abstract method rule in functional interfaces?