How Can I Initialize an ArrayList in Java Using a Single Line of Code?

Initialization of an ArrayList in One Line with List Interface

When initializing an ArrayList, developers often face the dilemma of choosing between readability and efficiency. The traditional method involves creating an empty ArrayList and manually adding elements, as shown in the first code snippet. However, this approach can become cumbersome for large lists.

A more concise alternative is to use the Arrays.asList method, as demonstrated in the second code snippet. This method takes an array of elements and returns an immutable List containing those elements. This List can then be assigned to an ArrayList, as in the third code snippet.

However, using Lists may be more beneficial in certain scenarios. Lists provide a more general interface compared to ArrayLists and can also be initialized in a single line. To initialize a List directly, one can use either the Arrays.asList method or the Collections.singletonList method. The former creates an immutable List, while the latter creates a List containing a single element.

For example:

List<String> places = Arrays.asList("Buenos Aires", "Córdoba", "La Plata");

List<String> places = Collections.singletonList("Buenos Aires");

Note that Lists are immutable, meaning any attempt to modify them will result in an exception. To create a mutable ArrayList from a List, one can use the following syntax:

ArrayList<String> places = new ArrayList<>(Arrays.asList("Buenos Aires", "Córdoba", "La Plata"));

Don't forget to import the necessary package:

import java.util.Arrays;
// or
import java.util.Collections;

In this way, one can initialize an ArrayList with a list of elements in a concise and efficient manner. The choice between using an ArrayList or a List depends on the specific requirements of the application.

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