Convert Set to array in Java

2022/7/12 1:29:53

编程Tag： Array new Set Java integer convert Arrays

本文主要是介绍Convert Set to array in Java，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

Convert Set to array in Java

This post will discuss how to convert a set to an array in plain Java, Java 8, and the Guava library.

1. Naive solution

A naive solution is to iterate over the given set and copy each encountered element in the Integer array one by one.

1 2 3 4 5 6 7 8 9

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = new Integer[set.size()]; int k = 0; for (Integer i: set) { array[k++] = i; } System.out.println(Arrays.toString(array));

2. Using `Set.toArray()` method

Set interface provides the toArray() method that returns an Object array containing the elements of the set.

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Object[] array = set.toArray(); System.out.println(Arrays.toString(array));

The JVM doesn’t know the desired object type, so the toArray() method returns an Object[]. We can pass a typed array to the overloaded toArray(T[] a) method to let JVM know your desired object type.

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = set.toArray(new Integer[set.size()]); System.out.println(Arrays.toString(array));

We can also pass an empty array of the specified type, and JVM will allocate the necessary memory:

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = set.toArray(new Integer[0]); System.out.println(Arrays.toString(array));

3. Using Java 8

In Java 8, we can use the Stream to convert a set to an array. The idea is to convert a given set to stream using Set.stream() method and use Stream.toArray() method to return an array containing the stream elements. There are two ways to do so:

⮚ Using Streams with method reference

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = set.stream().toArray(Integer[]::new); System.out.println(Arrays.toString(array));

⮚ Using Streams with lambda expression

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = set.stream().toArray(n -> new Integer[n]); System.out.println(Arrays.toString(array));

4. Using Guava Library

⮚ Using FluentIterable class:

The FluentIterable is an expanded Iterable API that provides similar functionality as Java 8’s Stream. We can get a fluent iterable that wraps an iterable set and returns an array containing all the elements from the fluent iterable.

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = FluentIterable.from(set).toArray(Integer.class); System.out.println(Arrays.toString(array));

⮚ Using Iterables class:

Guava’s Iterables class also provides the toArray() method that copies an iterable’s elements into an array.

1 2 3

Set<Integer> set = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5)); Integer[] array = Iterables.toArray(set, Integer.class); System.out.println(Arrays.toString(array));

That’s all about converting Set to array in Java.

这篇关于Convert Set to array in Java的文章就介绍到这儿，希望我们推荐的文章对大家有所帮助，也希望大家多多支持为之网！

Convert Set to array in Java

Convert Set to array in Java

1. Naive solution

2. Using Set.toArray() method

3. Using Java 8

4. Using Guava Library

相关编程文章

2. Using `Set.toArray()` method