Sentry Answers>Java>

Create ArrayList from array in Java

Create ArrayList from array in Java

Lewis D.

—

The Problem

You want to convert your standard Java array, such as the one below, to an ArrayList to take advantage of the dynamically allocated memory.

Click to Copy
String[] array = {"new", "String", "array"};

The Solution

The easiest way to convert to an ArrayList is to use the built-in method in the Java Arrays library: Arrays.asList(array). This method will take in a standard array and wrap it in the AbstractList class, exposing all the methods available to objects that implement the List interface.

Click to Copy
List<String> list = Arrays.asList(array);

It is important to note, however, that this has no effect on the actual data structure or data from the original code. This can catch some programmers out, as they may expect the new list object to behave like a true List. The example below will cause an UnsupportedOperationException:

Click to Copy
List<String> list = Arrays.asList(array);
list.remove(1);

This is because the underlying data structure is still a static array, therefore the size cannot be changed. To create a true ArrayList data structure, we need to instantiate a new instance of the ArrayList object:

Click to Copy
List<String> list = new ArrayList<>(Arrays.asList(array));

The code above will create a new ArrayList instance and use the data from our original array to populate its initial values. The memory for our list object will now be dynamically allocated, so method calls such as list.remove or list.add will work as expected.

In conclusion, we can create an ArrayList from a standard array quite easily using methods from core Java libraries as long as we are careful to instantiate the object correctly.

  • Sentry BlogException Handling in Java (with Real Examples)
  • Syntax.fmListen to the Syntax Podcast
  • Syntax.fm logo
    Listen to the Syntax Podcast

    Tasty treats for web developers brought to you by Sentry. Get tips and tricks from Wes Bos and Scott Tolinski.

    SEE EPISODES

Considered “not bad” by 4 million developers and more than 100,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.

learn more about sentryjoin our discord
© 2024 • Sentry is a registered Trademark
of Functional Software, Inc.