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)

妖狐艹你老母 2023-09-23 22:38 47阅读 0赞

> There are many ways to convert integer List to ArrayList where in this article we will be discussing out 2 approaches as below:
> 
> 1.  Using concept od streams in Java8
> 2.  Using Apache Commons Lang
> 3.  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