Is it possible to use a lambda function to store internal data or state?

Lambda functions in Java cannot directly store internal state between calls because they are essentially anonymous functions without their own state.

However, closures can be used, where a lambda captures external variables that can act as state. But these variables must be effectively final (final or effectively final), meaning they cannot be modified after initialization.

If you need to store mutable state, you typically create a class with fields and methods, and the lambda simply accesses these fields.

Example:

class Counter {
    private int count = 0;
    Runnable increment = () -> {
        count++;
        System.out.println("Count: " + count);
    };
}

Here, the lambda uses a class field to store state, but the lambda itself does not store state.