What does backward compatibility mean with respect to default methods in Java?

 Backward compatibility, in the context of default methods in Java, refers to the ability of existing interfaces to work properly with the introduction of default methods.

Before Java 8, interfaces in Java could only declare method signatures, and any class implementing an interface had to provide implementations for all of its methods. This design decision caused issues when trying to add new methods to existing interfaces because it would break all the classes implementing those interfaces.

To address this problem, Java 8 introduced default methods in interfaces. A default method is a method defined within an interface with a default implementation. It allows adding new methods to an interface without breaking the existing classes that implement that interface.

Backward compatibility means that existing classes that implement an interface prior to the addition of default methods will continue to work correctly without any modifications. These classes will still function with the same behavior as before, even though the interface they implement now has additional default methods.

In other words, backward compatibility ensures that existing code remains functional and unaffected when new methods with default implementations are added to an interface. This feature was introduced to make it easier to evolve interfaces and add new functionality to them without breaking existing codebases.