Writing your own interval type

You can add custom interval types of either of the two basic types of intervals:

• Iterable intervals, which are intervals that you can iterate across, such as in for loop declarations
• Non-iterable intervals

For typical code, iterable intervals are more useful because they can simplify common coding patterns in loops.

In some circumstances, you need to create a non-iterable interval. For example, suppose you want to encapsulate an inclusive range of real numbers between two endpoints. Such a set includes a theoretically infinite set of numbers between the values 1 and 1.001. Iterating across the set is meaningless.

The basic properties of an interval are as follows:

• The type of items in the interval must implement the Java interface java.lang.Comparable.
• The interval has left and right endpoints (the starting and ending values of the interval)
• Each endpoint can be closed (included) or open (excluded)

The main difference for iterable intervals is that they also implement the java.lang.Iterable interface.