Cat.java

public class Cat {
    private Bird caughtBird;
    private boolean isFull = false;

    public Cat catchBird(Bird bird) {
        if (caughtBird != null) {
            throw new RuntimeException("Caught one bird already");
        }
        caughtBird = bird;
        return this;
    }

    public Cat eat() {
        if (caughtBird == null) {
            throw new RuntimeException("Must catch a bird first");
        }
        this.caughtBird = null;
        this.isFull = true;
        return this;
    }

    public static void main(String[] args) {
        Cat cat = new Cat();
        Bird bird = new Bird();
        cat.eat().catchBird(bird); // calls out of order; 
                                   // throws exception
    }
}

Main.java

public class Story {
    public static void main(String[] args) {
        Bird bird = new Bird();
        HungryCat hungryCat = new HungryCat();
        hungryCat.catchBird(bird)
                .eat()
                .whackOnTheHead()
                .catchBird(bird)
                .eat()
                .whackOnTheHead(); // and repeat
    }
}

Story.java

class HungryCat {
    public CatWithPrey catchBird(Bird bird) {
        return new CatWithPrey(bird);
    }
}

class CatWithPrey {
    private Bird caughtBird;

    public CatWithPrey(Bird bird) {
        this.caughtBird = bird;
    }

    public FullCat eat() {
        return new FullCat();
    }
}

class FullCat {
    public HungryCat whackOnTheHead() {
        System.out.println("Whack! (Coughs up the bird)");
        return new HungryCat();
    }
}