Array and ArrayList are two common data structures used in Java programming language. Although they are similar in many ways, they have several key differences that make them suitable for different use cases. Understanding the differences between the two will help you choose the right data structure for your application.

An array is a fixed-size data structure that holds multiple values of the same data type. It is declared using the square bracket notation and the size of the array is specified at the time of creation. Once created, the size of an array cannot be changed. This means that you cannot add or remove elements from an array after its creation. However, you can access and modify the elements in an array.

On the other hand, an ArrayList is a dynamic data structure that can hold multiple values of different data types. It is created using the ArrayList class and can grow or shrink in size dynamically. Unlike an array, the size of an ArrayList can be changed as required, making it a more flexible and convenient data structure. You can add or remove elements from an ArrayList at any time, and it automatically resizes itself accordingly.

Another important difference between arrays and ArrayLists is their performance. Arrays are generally faster than ArrayLists when it comes to accessing elements. This is because arrays are stored in contiguous memory locations, which makes it easier for the processor to access elements. ArrayLists, on the other hand, are implemented as dynamic arrays, meaning that the elements are stored in multiple memory locations that are not contiguous. This means that accessing elements in an ArrayList is slower than in an array.

In terms of memory usage, arrays are more memory-efficient than ArrayLists because they have a fixed size. ArrayLists, on the other hand, use more memory because they have to allocate memory dynamically to store new elements.