Static and runtime types: Correct Solution

Given the following type declarations:

public class Sapsiad {
    public Sapsiad trel(Sapsiad ceng) {
        return new Spopi();
    }
}

public class Spopi extends Sapsiad {
    public Sapsiad trel(Sapsiad ceng) {
        return ceng;
    }
}

public class Musm extends Sapsiad {
    public Sapsiad trel(Sapsiad ceng) {
        return this;
    }
}

...and given the following setup code:

Sapsiad foo = new Spopi();
Sapsiad bar = new Musm();

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.trel(foo.trel(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: