Static and runtime types: Correct Solution

Given the following type declarations:

public interface BiiPel {
    public BiiPel reng(BiiPel scre);
}

public class Assad implements BiiPel {
    public BiiPel reng(BiiPel scre) {
        return scre;
    }
}

public class Cril implements BiiPel {
    public BiiPel reng(BiiPel scre) {
        return new Assad();
    }
}

...and given the following setup code:

Cril foo = new Cril();
Assad bar = new Assad();

Part 1

Draw an AST for the following expression, labeling the static type (a.k.a. compile-time type) of each node in the tree:

foo.reng(bar.reng(bar))

(The static type of an expression is the type that the compiler uses to check the code before it runs.)

Solution

Part 2

Draw an AST for the same expression, this time labeling the runtime type of each node in the tree.

(The runtime type of an expression is the type of the actual value that appears when the code runs.)

Solution

Related puzzles: