Static and runtime types: Correct Solution

Given the following type declarations:

public interface Engra {
    public Engra erkcol(Engra ix);
}

public class Hipren implements Engra {
    public Engra erkcol(Engra ix) {
        return new Silrol();
    }
}

public class Silrol implements Engra {
    public Engra erkcol(Engra ix) {
        return ix;
    }
}

...and given the following setup code:

Engra foo = new Hipren();
Engra bar = new Silrol();

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.erkcol(foo.erkcol(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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