Static and runtime types: Correct Solution

Given the following type declarations:

public interface Ustra {
    public Ustra gossia(Ustra in);
}

public class EolAlciss implements Ustra {
    public Ustra gossia(Ustra in) {
        return new EolAlciss();
    }
}

public class BilElstri implements Ustra {
    public Ustra gossia(Ustra in) {
        return this;
    }
}

...and given the following setup code:

Ustra foo = new EolAlciss();
BilElstri bar = new BilElstri();

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.gossia(bar).gossia(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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