What is a default method and why is it required?

What is it?

A method in an interface that has a body and is marked with the default keyword.

Why was it required?

• Backward Compatibility: To add new methods to existing interfaces (like Iterable.forEach or Collection.stream) without breaking the classes that implement those interfaces.
• Before Java 8, adding a method to an interface required all implementing classes to provide an implementation, which was impossible for core libraries used by millions.