Solved: initialize list with values

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Initializing a list with values in Java is a commonly required operation for developers. It’s often seen that Java programmers have to deal with operations such as creating a list, adding values to it and then performing operations on the list. This process can be tiresome if not handled appropriately. Therefore, an understanding of efficient ways to initialize lists with values can significantly streamline programming tasks.

The article will offer an understanding of how to initialize lists with values in Java using various methods and libraries.

Direct Initialization

The most straightforward way of initializing a list with values is by using Add() method of list class. This method adds an element at the end of the list.

Let’s consider an example:

List<String> list = new ArrayList<>();

list.add("Element1");
list.add("Element2");
list.add("Element3");

The new list now contains three elements Element1, Element2, and Element3.

However, the method is not efficient when a large number of elements are to be added. More efficient solutions are discussed below.

Using Arrays.asList()

Java provides Arrays class from its java.util package. The class contains various methods for manipulating arrays. The asList() method of this class is static and returns a fixed-size list backed by the specified array.

Let’s understand with an example:

List<String> list = Arrays.asList("Element1", "Element2", "Element3");

The method is handy and efficient, but the returned list is immutable. If you try to add or remove elements from the list, it will throw a java.lang.UnsupportedOperationException exception.

Using Collections

Collections class of java.util package is a utility class having static methods for doing operations on objects of classes which implement the Collection framework. There is a method ncopies(int n, Object obj) which returns an immutable list containing specified number of copies of the specified object.

Example usage of the method:

List<String> list = Collections.nCopies(3, "Element");

In this method, all elements of the list are initialized to the specified object, thus all elements of the list are the same.

Using Java 8 Stream

Java 8 introduced a new Stream API which can be used to initialize a list with values in a few lines of code.

List<String> list = Stream.of("Element1", "Element2", "Element3")
                          .collect(Collectors.toList());

In this code, Stream.of() method returns a sequential ordered stream whose elements are the specified values. The collect() method is a terminal operation which collects the result into various data structures and here it collects the stream elements to a List.

Conclusion

So these are a few of the methods to initialize a list with values in Java. While dealing with lists in Java, users have a variety of options depending on the requirements of their context. For instance, to create a fixed-size list with many copies of the same element, the ncopies method of Collections class can be used. When working with arrays, Arrays.asList() comes in handy. For users looking to leverage Java 8’s features, Stream API offers a succinct syntax to streamline list operations. As always, choosing the right method greatly depends on the specific needs and restrictions of a project.

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