Understanding the Difference Between a List and an ArrayList in Java

List vs ArrayList in Java

When it comes to working with data collections, developers often need to choose between the List and ArrayList in Java. Both the List and ArrayList interfaces are part of the Java Collection Framework and provide a way to store and manipulate data. But, when and why should developers use one over the other?

What is a List?

The List interface is a part of Java’s collection framework. It’s an ordered collection and permits duplicate elements. This means that a List can store multiple values of the same type and will maintain the order in which they were added to the list. It also provides various methods to manipulate its elements.

The List interface uses generics, meaning that you can specify the type of objects it stores. To use the List, a class has to implement it. Classes like ArrayList, LinkedList, Vector, and Stack, which are all subclasses of AbstractList, are commonly used to implement this interface.

What is an ArrayList?

An ArrayList is a dynamic array that stores elements in contiguous memory locations. It’s a powerful implementation of the List interface and provides more options for manipulating the stored data. An ArrayList is an ordered list of items and can hold duplicate values. It follows the principle of LIFO and FIFO – Last In First Out and First In First Out. Moreover, it’s dynamic in nature, meaning that it can expand or shrink in size.

Differences between List and ArrayList

When it comes down to comparing List vs ArrayList, there are some key points to consider:

• Performance: ArrayList offers better performance than List as it performs operations such as search, insert, delete, etc. much faster.
• Elements: Both store elements of different data types, but List only stores homogeneous elements while ArrayList can store heterogeneous elements.
• Synchronization: ArrayList is not thread-safe, so operations on it aren't synchronized. List, however, is thread-safe, so operations on it are synchronized.
• Growability: ArrayList automatically expands when new elements are added to it. List doesn't grow automatically, so it requires manual expansion.

In conclusion, List and ArrayList are two useful interfaces in Java which serve different purposes. The choice between the two depends on whether you want a thread-safe list or a more performant list.