How does default methods in interfaces behave in multithreaded code?

Default methods in interfaces in Java allow developers to add new methods to interfaces without breaking the existing implementations. However, when dealing with multithreaded code, the behavior of these default methods can become complex. Because default methods can modify shared states, care must be taken to ensure thread safety.

For example, if a default method accesses or modifies a shared variable, synchronizing access can prevent issues such as race conditions. However, if multiple threads call the default method concurrently, it can lead to unexpected behavior unless properly synchronized.