What's the Most Efficient Way to Initialize an ArrayList in Java?

Initializing an ArrayList in a Single Line: Exploring Various Approaches

To initialize an ArrayList with specific elements, developers often face the dilemma of choosing the most efficient and succinct method. One widely used approach involves using the new keyword, creating an empty ArrayList, and subsequently adding elements using the add method.

However, a more concise solution is to leverage the asList method on the Arrays class. By passing an array of values to asList, one can create an immutable list. Wrapping this list in an ArrayList constructor converts it into a mutable list that supports adding and removing elements.

For instance, consider the following code:

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

This approach combines the advantages of both the new keyword and the asList method, allowing for the initialization of an ArrayList with a single line of code.

But is there a simpler option? If the requirement is not explicitly an ArrayList, one can utilize the List interface instead. The Arrays.asList method can create an immutable list without the need for wrapping it in an ArrayList.

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

For scenarios where only a single element is present, the Collections.singletonList method serves as a neater alternative.

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

Using the singletList method ensures immutability, meaning that any attempt to modify the resulting list will result in an exception. For mutable lists, consider wrapping the immutable list in an ArrayList.

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

Remember to import the java.util.Arrays package for this approach.

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