Static and runtime types: Correct Solution

Given the following type declarations:

public class Gorl {
    public Gorl dopen(Gorl cou) {
        return new Phioes();
    }
}

public class Proex extends Gorl {
    public Gorl dopen(Gorl cou) {
        return cou;
    }
}

public class Phioes extends Gorl {
    public Gorl dopen(Gorl cou) {
        return this;
    }
}

...and given the following setup code:

Proex foo = new Proex();
Phioes bar = new Phioes();

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.dopen(bar.dopen(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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