Quiz J3-2

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Question 1

Say we have the class Shelf below.

class Shelf<T> {
    List<T> shelfItems;

    public Shelf() {
        shelfItems = new ArrayList<T>();
    }
    int addItem(T item){
        shelfItems.add(item);
        return shelfItems.size()-1;
    }

    void printShelf(){
        for(T item: shelfItems)
            System.out.println(item.toString()+" ");
    }
}

What is the output of this program?

  public static void main(final String args[]) {
      Shelf<int> favorite_numbers = new Shelf();
      favorite_numbers.addItem(5);
      favorite_numbers.addItem(10);
      favorite_numbers.printShelf();
  }

Question 2

Now we add a function to build shelves to Shelf:

    static Shelf<T> shelfBuilder(){
        return new Shelf<T>();
    }

What’s the output of this new program?

    public static void main(final String args[]) {
        Shelf<String> favorite_words = Shelf.shelfBuilder();
        favorite_words.addItem("Zoetrope");
        favorite_words.addItem("Succinct");
        favorite_words.printShelf();
    }

Question 3

Suppose we add a new method to Shelf to retrieve an item by the index in which it was added:

class Shelf<T> {
    List<T> shelfItems;
    
    //... same as Question 1
    
    T getItem(int idx){return shelfItems.get(i);}
}

Given the program below:
```java
    public static void main(final String args[]) {
        Shelf<String> favorite_words = shelfBuilder();
        favorite_words.addItem("Zoetrope");
        favorite_words.addItem("Succinct");
        //...        
        String s = favorite_words.getItem(1);
        System.out.println(s);
    }

What does this method erase to when the program compiles and the generics is removed?

    //Option one
    public static void main(final String args[]) {
        Shelf<String> favorite_words = shelfBuilder();
        favorite_words.addItem((Object) "Zoetrope");
        favorite_words.addItem((Object) "Succinct");
        //...        
        String s = favorite_words.getItem(1);
        System.out.println(s);

        ...
    }

    // Option two
    public static void main(final String args[]) {
        Shelf<Object> favorite_words = shelfBuilder();
        favorite_words.addItem((Object) "Zoetrope");
        favorite_words.addItem((Object) "Succinct");
        //...        
        String s = favorite_words.getItem(1);
        System.out.println(s);
    }

    // Option three
    public static void main(final String args[]) {
        Shelf favorite_words = shelfBuilder();
        ...
        favorite_words.addItem( "Zoetrope");
        favorite_words.addItem( "Succinct");
        //...        
        String s = (String) favorite_words.getItem(1);
        System.out.println(s);

    }

    // Option four
        public static void main(final String args[]) {
        Shelf favorite_words = shelfBuilder();
        ...
        favorite_words.addItem((Object) "Zoetrope");
        favorite_words.addItem((Object) "Succinct");
        //...        
        String s = (String) favorite_words.getItem(1);
        System.out.println(s);

    }

Question 4

Finally consider this Fibonacci generator class:

class Fibonacci implements Iterable<Integer> {
    int max;

    public Fibonacci(int max) {
        this.max = max;
    }

    public Iterator<Integer> iterator() {
        return new FibonacciIter();
    }

    class FibonacciIter implements Iterator<Integer> {
        int current = 1;
        int previous = 0;

        @Override
        public boolean hasNext() {
            return current+previous <= max;
        }

        @Override
        public Integer next() {
            int tmp = current;
            current += previous;
            previous = tmp;
            return current;
        }
    }
}

What is the output of the below?

    public static void main(final String args[]) {
        Fibonacci fibonacci = new Fibonacci(13);
        for (Integer i : fibonacci)
            System.out.print(i+" ");
        fibonacci.max = 21;
        for (Integer i : fibonacci)
            System.out.print(i + " ");
    }