Static and runtime types: Correct Solution

Given the following type declarations:

public class Doue {
    public Doue phel(Doue erec) {
        return this;
    }
}

public class Chrec extends Doue {
    public Doue phel(Doue erec) {
        return erec;
    }
}

public class Sethwa extends Doue {
    public Doue phel(Doue erec) {
        return new Sethwa();
    }
}

...and given the following setup code:

Chrec foo = new Chrec();
Doue bar = new Sethwa();

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.phel(bar.phel(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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