Java将整数列表转换为整数数组3种方法(Java Program to Convert Integer List to Integer Array)

There are many ways to convert integer List to ArrayList where in this article we will be discussing out 2 approaches as below:

Using concept od streams in Java8
Using Apache Commons Lang
Using Guava Library

1.Using concept od streams in Java8

In java 8 there is a stream provided for converting a list of integer to an integer array.
Convert List to Stream using List.stream() —> Here List is calling stream() method.
Now we convert Stream to int[].

public class A{
    public static void main(String[] args)
    {
        // Creating an List of integer type and
        // customly inserting input elements a arguments
        List<Integer> list = Arrays.asList(1, 3, 5, 7, 9);
        // Converting Stream<Integer> to integer array
        // using stream() and mapToInt() methods, lately
        // storing them in an integer array
        int[] primitive = list.stream()
                .mapToInt(Integer::intValue)
                .toArray();
        // Print and display the integer array
        System.out.println(Arrays.toString(primitive));
    }
}
[1, 3, 5, 7, 9]

2.Using Apache Commons Lang

Apache Commons Lang’s ArrayUtils class provides toPrimitive() method that can convert an Integer array to primitive ints. We need to convert a list of integers to an Integer array first. We can use List.toArray() for easy conversion.
Procedure:
1.Use toPrimtive() method of Apache Common Lang’s
2.Use List.toArray() method

public class A{
    public static void main(String[] args)
    {
        // Creating an object of List class of integer type
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
        // Using toPrimtive() method of Apache Common Lang's
        int[] primitive = ArrayUtils.toPrimitive(
            list.toArray(new Integer[0]));
        // Print and display the integer array
        System.out.println(Arrays.toString(primitive));
    }
}
[1,2,3,4,5]

3.Using Guava Library

Guava library is an open-source decentralized software development model which is a set of common libraries of java providing utility methods for collections, caching, primitives support, concurrency, string processing, and validations.
Here we will be glancing at string processing in the guava library by converting integer list to integer array.

// Java Program to Convert List to Integer Array
// Using Guava Library
// Importing required classes
import com.google.common.primitives.Ints;
import java.util.Arrays;
import java.util.List;
// Main class
class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Creating an object of List class of integer type
        List<Integer> ints = Arrays.asList(3, 7, 8, 6, 1);
        // Converting a list of Integer to primitive integer
        // array and storing in integer array
        int[] primitive = Ints.toArray(ints);
        // Print and display the integer array via Guava
        // by converting it to string
        // via standard toString() method
        System.out.println(Arrays.toString(primitive));
    }
}
3,7,8,6,1