Arraylists are a dynamic version of an array. It has special features that allow you to change the size of the arraylist. Java has a class that implements arraylists with arrays. The adding and removing function copies values from one array to another of a different size, therefore functionality is not super efficient.
To use arraylists, you need to import, allowing you to access the premade Java class implementation of an arraylist.
You can replace the “String” with any object type (note that primitive types do not work, use Integer class for ints, Double class for doubles, etc)