How does inner and nested classes behave in multithreaded code?

In Java, both inner and nested classes can be utilized in multithreaded environments. Understanding their behavior is crucial for ensuring thread safety and managing shared resources effectively.

Inner classes are associated with an instance of their enclosing class and can access its instance variables and methods even if they are declared private. This can lead to shared state issues in a multithreaded context if multiple threads access the same instance of the enclosing class.

On the other hand, static nested classes do not have a reference to an enclosing instance and cannot access instance variables of the outer class unless they are static. This makes them a safer option in certain multithreaded scenarios as they do not rely on the state of the enclosing class instance.

When using any type of class in a multithreaded environment, it is essential to manage synchronization and resource sharing to avoid issues such as data corruption and race conditions.