Why does not compute function give error while converting Integer to double?

Question

Why is below code working fine and not complaining about return type of Function being an Integer instead of Double?

    public static void main(String[] args) {
          double principle = 100;         
          int interestrate = 5;         
          double amount = compute(principle, x->x*interestrate);
    }
    public static double compute(double base, Function<Integer, Integer > func){ 
        return func.apply((int)base); 
    }

Answer 1

It's happened because java automatically converting types if it does not lead to loss of accuracy. It can convert int to double, but not convert double to int because the decimal part will be lost (but of course you can do it manually). You can read about it here https://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html