During the first week, you learned about the core elements of the Java language: objects, classes, and interfaces, along with the keywords, statements, expressions, and operators they contain.
For the second week, the focus shifts from the classes you create to the ones that have been created for you. The Java Class Library is a set of standard packages from Oracle that has more than 4,200 classes you can use in your own Java programs.
Today, you start with classes that represent data.
The following data structures are covered:
Bit sets, which hold Boolean values
Array lists, arrays that can grow and shrink in size