Introduction:

In Java, working with collections is an essential aspect of programming. Sometimes, we encounter situations where we need to convert a List into an Array or vice versa. In this blog, we will focus on converting a List to an Array using different methods. We will explore several approaches, explain their differences, and provide code examples with outputs to clarify each method's usage. By the end of this tutorial, you will have a comprehensive understanding of converting Lists to Arrays in Java.

Method 1: Using toArray() Method

The toArray() method is a straightforward way to convert a List to an Array. This method is provided by the List interface in Java. The returned array will be of type Object[], which we will need to cast to the appropriate type.

List<String> stringList = new ArrayList<>();
stringList.add("Java");
stringList.add("is");
stringList.add("awesome");

// Converting List to Array
String[] stringArray = stringList.toArray(new String[0]);

In this method, we call the toArray() method on the List object stringList and pass an empty array of the desired type (in this case, new String[0]). The toArray() method then copies the elements from the List to the new array and returns the new array.

Output:

The stringArray will now contain ["Java", "is", "awesome"].

Method 2: Using the Stream API

Java 8 introduced the Stream API, which provides a concise way to convert a List to an Array.

List<Integer> integerList = Arrays.asList(1, 2, 3, 4, 5);

// Converting List to Array using Stream API
Integer[] integerArray = integerList.stream().toArray(Integer[]::new);

In this method, we first convert the List integerList to a Stream using the stream() method. Then, we use the toArray() method provided by the Stream class, passing a method reference Integer[]::new that specifies the array constructor to be used.

Output:

The integerArray will now contain [1, 2, 3, 4, 5].

Method 3: Using Apache Commons Lang Library

If you want a more generic solution that works with different types of Lists, you can use the toArray() method from the Apache Commons Lang library.

import org.apache.commons.lang3.ArrayUtils;

List<Double> doubleList = new LinkedList<>();
doubleList.add(3.14);
doubleList.add(1.618);
doubleList.add(2.718);

// Converting List to Array using Apache Commons Lang
Double[] doubleArray = ArrayUtils.toArray(doubleList);

In this method, we use the ArrayUtils.toArray() method from the Apache Commons Lang library, which automatically converts the List to the appropriate type of array.

Output:

The doubleArray will now contain [3.14, 1.618, 2.718].

Method 4: Using Manual Conversion

In situations where you don't want to use external libraries or prefer a manual approach, you can manually convert the List to an array by iterating through the List and copying its elements to the array.

List<Character> charList = Arrays.asList('a', 'b', 'c');

// Converting List to Array manually
Character[] charArray = new Character[charList.size()];
for (int i = 0; i < charList.size(); i++) {
    charArray[i] = charList.get(i);
}

In this method, we create a new array charArray with the same size as the List. We then iterate through the List charList, copying each element to the corresponding index in the array.

Output:

The charArray will now contain ['a', 'b', 'c'].

Method 5: Using Java 11+ List.toArray()

In Java 11 and later versions, a new method List.toArray(IntFunction<T[]>) was introduced, which simplifies the conversion process.

List<Boolean> booleanList = List.of(true, false, true);

// Converting List to Array using List.toArray(IntFunction<T[]>)
Boolean[] booleanArray = booleanList.toArray(Boolean[]::new);

In this method, we call the toArray(IntFunction<T[]>) method on the booleanList, passing the array constructor Boolean[]::new as an argument.

Output:

The booleanArray will now contain [true, false, true].

Conclusion:

This blog explored various methods to convert a List to an Array in Java. We learned the straightforward approach using toArray() method, the powerful Stream API, the convenience of Apache Commons Lang library, manual conversion, and the simplified method introduced in Java 11+. Each method has its advantages and can be chosen based on specific requirements and personal preferences. Understanding these techniques will enable you to effectively convert Lists to Arrays and enhance your Java programming skills.