I am not very familiar with Java details. Can you explain why this doesn't compile?

It's this part:

    int i;
    {
        int i;
    }

Java does not allow you to shadow one local variable with another.

This is ok:

    {
        int i;
    }
    int i;

because the scopes do not overlap.

This is ok too:

    int i;
    {
        class LocalClass {
            public void method() {
                int i;
            }
        }
    }