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Arrays asList() method in Java with Examples
  • Difficulty Level : Easy
  • Last Updated : 05 Nov, 2020

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




// 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);
        }
    }
}
Output
The list is: [A, B, C, D]

Example 2: 

Java




// 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);
        }
    }
}
Output
The list is: [10, 20, 30, 40]

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