Where in memory is the ArrayList data structure stored?

In Java, an ArrayList object is stored in the heap. The ArrayList object itself is an instance of a class that contains an internal field — an Object[] array, where the list elements are stored.

When creating an ArrayList, memory is allocated in the heap for the object and for the internal array (which can expand when elements are added). A variable referencing the ArrayList is usually located on the stack (if local) and contains a reference to the object in the heap.

Thus, the entire data structure of the ArrayList and its contents are placed in the managed JVM heap.