How to convert a String into an ArrayList?

java

list-operations

string-manipulation

performance-optimization

byAnton Shumikhin·Sep 23, 2024

To convert a String into an ArrayList, you can use the .split() function to divide it into segments. Then, employ the ArrayList constructor with Arrays.asList(). Here's how:

String example = "one, two, three";
// If you "split" the String, does it make a sound? Let's find out..
ArrayList<String> result = new ArrayList<>(Arrays.asList(example.split(", ")));

This approach divides the example String by ", " and directly uses the resulting array to create an ArrayList named result.

Breaking down the conversion process

To fully grasp how to transform a string into an ArrayList, understanding the detailed process is crucial. Let's break down the various components of this operation.

Editing the delimiters

In some scenarios, the components of your string may not be separated by a simple comma and space (", "). In these cases, you would need to adjust the delimiter in your .split() function:

String example = "one;two;three";
// After all, semicolons need love too.
ArrayList<String> result = new ArrayList<>(Arrays.asList(example.split(";")));

Here, we've changed the delimiter to a semicolon, ensuring our method is adaptable to varied data formats.

Dealing with dirty data

At times, you may encounter strings replete with additional spaces or inconsistent formatting. In these situations, it's wise to sanitize your strings before splitting:

String dirtyExample = " one , two,  three ";
// Nothing like a good sanitizing to get that fresh string smell!
String cleanExample = dirtyExample.trim().replaceAll("\\s*,\\s*", ",");
ArrayList<String> result = new ArrayList<>(Arrays.asList(cleanExample.split(",")));

Using replaceAll("\\s*,\\s*", ","), we manage to eradicate spaces, while trim() takes care of pesky leading or trailing spaces.

Immutability concerns

One critical thing to note is that Arrays.asList() hands out a fixed-size list. It's a solid choice where you don't need to add or remove elements in the future. For making a mutable list, the above solution takes the cake as it wraps the fixed-size list inside an ArrayList.

Using List.of() in Java 9+

For Java 9 and onward, you can use List.of() to create an immutable list:

List<String> immutableList = List.of(example.split(", "));

This method is handy when you don't anticipate or need to alter the data.

Pondering performance

Our initial solution curtails object creation by converting an array into an ArrayList directly. It's a performance-friendly strategy that you'll appreciate when dealing with bulky datasets.

Jazzing up with regex

If you fancy more elaborate splitting rules, regular expressions (regex) can lend a helping hand:

String complexData = "one, two, (three), four";
// Who says regex isn't fun?
ArrayList<String> complexResult = new ArrayList<>(
    Arrays.asList(complexData.split(",\\s*(?![^()]*\\))"))
);