Static and runtime types: Correct Solution

Given the following type declarations:

public interface NenUcu {
    public NenUcu spes(NenUcu et);
}

public class Ruaco implements NenUcu {
    public NenUcu spes(NenUcu et) {
        return this;
    }
}

public class Sistem implements NenUcu {
    public NenUcu spes(NenUcu et) {
        return et;
    }
}

...and given the following setup code:

NenUcu foo = new Ruaco();
NenUcu bar = new Sistem();

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.spes(bar.spes(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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