To create an ArrayList, we need to declare the type of objects it will hold, just as we do with arrays:

ArrayList<String> babyNames;

We use angle brackets < and > to declare the type of the ArrayList. These symbols are used for generics. Generics are a Java construct that allows us to define classes and objects as parameters of an ArrayList. For this reason, we can’t use primitive types in an ArrayList:

// This code won't compile:
ArrayList<int> ages;

// This code will compile:
ArrayList<Integer> ages;

The <Integer> generic has to be used in an ArrayList instead. You can also use <Double> and <Char> for types you would normally declare as doubles or chars.

We can initialize to an empty ArrayList using the new keyword:

// Declaring:
ArrayList<Integer> ages;
// Initializing:
ages = new ArrayList<Integer>();

// Declaring and initializing in one line:
ArrayList<String> babyNames = new ArrayList<String>();