Static and runtime types: Correct Solution

Given the following type declarations:

public interface Dengno {
    public Dengno ensi(Dengno cuil);
}

public class Bensu implements Dengno {
    public Dengno ensi(Dengno cuil) {
        return new Bost();
    }
}

public class Bost implements Dengno {
    public Dengno ensi(Dengno cuil) {
        return cuil;
    }
}

...and given the following setup code:

Bensu foo = new Bensu();
Bost bar = new Bost();

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.ensi(bar.ensi(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

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