Iterators

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We use them in loops. For example, for(int num: nums) in java.

It is helpful in abstraction as the caller does not need to know the underlying data structure.

There are two commonly used methods

1. next() -> Moves to the next element. Note that this is an irreversible operation and changes the internal state of the iterator permanently. We are not able to go back in reverse.
2. hasNext() -> Check if there is a next element to go to.

Properties

1. Only need to know how to get the next element, and we do not need to store the entire data in memory.
   Imagine it as iterating a Linked list, where we keep moving from head to the end. As items are consumed, they are discarded and the next element is replaced with it.
2. Can use it to represent sequences without incurring memory, O(1). For example, if we want to iterate through a range of values.
3. Support infinite data.

public class RangeIterator {
    private final int max;
    private int current;

    public RangeIterator(int min, int max) {
        this.current = min…