Why can we not use default methods in lambda expressions?

Question

I was reading this tutorial on Java 8 where the writer showed the code:

interface Formula {
    double calculate(int a);

    default double sqrt(int a) {
           


        

Answer 1

This adds little to the discussion, but I found it interesting anyways.

Another way to see the problem would be to think about it from the standpoint of a self-referencing lambda.

For example:

Formula formula = (a) -> formula.sqrt(a * 100);

It would seem that this ought to make sense, since by the time the lambda gets to be executed the formula reference must have already being initialized (i.e. there is not way to do formula.apply() until formula has been properly initialized, in whose case, from the body of the lambda, the body of apply, it should be possible to reference the same variable).

However this does not work either. Interestingly, it used to be possible at the beginning. You can see that Maurice Naftalin had it documented in his Lambda FAQ Web Site. But for some reason the support for this feature was ultimately removed.

Some of the suggestions given in other answers to this question have been already mentioned there in the very discussion in the lambda mailing list.