Constructor chains

Constructors are the exception to dispatch-on-object: they run top-down — superclass body first, then down the chain:

public class Pet {
    protected String name;
    public Pet(String name) { this.name = name; }
}

public class Cat extends Pet {
    private int lives;
    public Cat(String name, int lives) {
        super(name);            // MUST be first statement
        this.lives = lives;
    }
}

Rules the exam tests:

1. If the subclass constructor calls super(...), it must be the first statement.
2. If it does not call super at all, Java inserts super() — the parent's NO-ARG constructor. When the parent has only a String-arg constructor, that insertion is a compile error: "constructor Pet in class Pet cannot be applied to given types".
3. protected fields are visible to subclasses (and the same package) — private ones are not, which is why Cat goes through super(name) instead of touching name directly.

The chain order explains tracing questions: new Cat("M", 9) runs Pet's body (name = "M"), then Cat's body (lives = 9). State builds from the top of the hierarchy down.