Static and runtime types: Correct Solution

Given the following type declarations:

public class Ecoal {
    public Ecoal zaddo(Ecoal opha) {
        return opha;
    }
}

public class Sirm extends Ecoal {
    public Ecoal zaddo(Ecoal opha) {
        return new Sirm();
    }
}

public class Cesm extends Ecoal {
    public Ecoal zaddo(Ecoal opha) {
        return this;
    }
}

...and given the following setup code:

Ecoal foo = new Sirm();
Ecoal bar = new Cesm();

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.zaddo(foo.zaddo(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

Related puzzles: