Comparables and Iterators

Notes from Josh Hug's lecture videos.

Iterators

Iterators are useful for data structures that store objects, as they allow users to go through them one by one. Syntax wise, if Steven is a data structure, then we must do the following.

1. Steven<T> implements Iterable<T>. It implements its interface method, iterator();, that returns a StevenIterator.

2. The Steven class should have a StevenIterator subclass, that implements Iterable<T>.

3. StevenIterable should implement Iterable's interface methods, T next(); and boolean hasNext();.

4. StevenInstance.iterator(); should return new StevenIterator();.

Many Java built-in data structures, such as ArrayList and LinkedList, already implement Iterable<T>, which is useful because you can get an Iterator object from them whenever you want.

If an object implements Iterable, you can use an enhanced for loop on it.

for (int i : lst) {
    System.out.println(i);
}

Comparables

A lot of data structures, such as BSTs, rely on objects being comparable. We can make any object we want comparable by doing the following.

1. The object should implement Comparable.

2. The object should then implement its interface method, int compareTo(T item);. This method usually returns negative if the object invoking it is less than item, positive if vice versa, and zero if equal.