Static and runtime types: Correct Solution

Given the following type declarations:

public interface Balpa {
    public Balpa lidse(Balpa hec);
}

public class Helprod implements Balpa {
    public Balpa lidse(Balpa hec) {
        return hec;
    }
}

public class Barsspos implements Balpa {
    public Balpa lidse(Balpa hec) {
        return new Barsspos();
    }
}

...and given the following setup code:

Helprod foo = new Helprod();
Barsspos bar = new Barsspos();

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.lidse(foo.lidse(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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