An ArrayList is backed up by array internally. There are many

usability advantages of using an ArrayList over an array in Java.

Array has a fixed length at the time of creation. Once it is created

we cannot change its length.

ArrayList is dynamic in size. Once it reaches a threshold, it

automatically allocates a new array and copies contents of old array

to new array.

Also ArrayList provides support of Generics. But Array does not

support Generics.

E.g. If we store an Integer object in a String array at Runtime it will

throw ArrayStoreException. Whereas, if we use ArrayList then as

compile time we will get the error. This helps in preventing errors

from happening at runtime.

If we know the size in advance and do not need re-sizing the

collection then Array should be used in place of an ArrayList

https://www.geeksforgeeks.org/array-vs-arraylist-in-java/