Arrays asList() method in Java with Examples

The asList() method of java.util.Arrays class is used to return a fixed-size list backed by the specified array. 
This method acts as bridge between array-based and collection-based APIs, in combination with Collection.toArray(). The returned list is serializable and implements RandomAccess.
This runs in O(1) time. 
Syntax: 

public static List asList(T... a)

Parameters: This method takes the array a which is required to be converted into a List.  Here … is  known as varang which is an array of parameters and works similar to an object array parameter.

NOTE : The type of array must be a Wrapper Class(Integer,FLoat, etc) in case of primitive data types(int,float,etc) , i.e you can’t pass  int a[] but you can pass Integer a[]. If you pass int a[],this function will return a  List <int a[]> and not List <Integer> , as “autoboxing” doesn’t happens in this case and  int a[] is itself identified as an object and a List of int array is returned, instead of list of integers , which will give error in various Collection functions .

Return Value: This method returns a list view of the specified array.
Below are the examples to illustrate the asList() method.

Example 1: 



Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to demonstrate
// asList() method for String value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
 
        try {
 
            // creating Arrays of String type
            String a[]
                = new String[] { "A", "B", "C", "D" };
 
            // getting the list view of Array
            List<String> list = Arrays.asList(a);
 
            // printing the list
            System.out.println("The list is: " + list);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

chevron_right


Output

The list is: [A, B, C, D]

Example 2: 

Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to demonstrate
// asList() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
 
        try {
 
            // creating Arrays of Integer type
            Integer a[] = new Integer[] { 10, 20, 30, 40 };
 
            // getting the list view of Array
            List<Integer> list = Arrays.asList(a);
 
            // printing the list
            System.out.println("The list is: " + list);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

chevron_right


Output

The list is: [10, 20, 30, 40]

Attention reader! Don’t stop learning now. Get hold of all the important Java and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.




My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Improved By : olympusx, curiousno1

Article Tags :
Practice Tags :


3


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.