Static and runtime types: Correct Solution

Given the following type declarations:

public interface Sasu {
    public Sasu aein(Sasu pasm);
}

public class Hithpla implements Sasu {
    public Sasu aein(Sasu pasm) {
        return new Eorash();
    }
}

public class Eorash implements Sasu {
    public Sasu aein(Sasu pasm) {
        return this;
    }
}

...and given the following setup code:

Hithpla foo = new Hithpla();
Eorash bar = new Eorash();

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.aein(bar).aein(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: