Stream

Stream - can be formed from any object that implements the Collection Interface
(e.g., ArrayList, HashSet, HashMap) with the stream() method

Stream methods has two categories:
1. Intermediate operations - transform or filter the elements of a stream, returning a
new stream as a result (e.g., distinct(), filter(), mapToInt(), sorted())
2. Terminal operations - produce a final result or side effect, consuming the elements
of a stream (e.g., count(), collect(), forEach(), reduce())


Lambda Expression - shorthand
A lambda expression is a concise way to represent an
anonymous function or behavior that can be passed around as a value.

Anonymous function
- does not need a named function declaration
- use inline or as a parameter to other functions or methods
- defined without a specific name