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 a bridge between array-based and collection-based APIs, in combination with Collection.toArray(). The returned list is serializable and implements RandomAccess.
Tip: 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 varargs which is an array of parameters and works similar to an object array parameter.
Special 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 happen 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.
Example 1:
Java
// Java program to Demonstrate asList() method// of Arrays class for a string value// Importing utility classesimport java.util.*;// Main classpublic class GFG { // Main driver method public static void main(String[] argv) throws Exception { // Try block to check for exceptions 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 all the elements in list object System.out.println("The list is: " + list); } // Catch block to handle exceptions catch (NullPointerException e) { // Print statement System.out.println("Exception thrown : " + e); } }} |
The list is: [A, B, C, D]
Example 2:
Java
// Java program to Demonstrate asList() method// of Arrays class For an integer value// Importing utility classesimport java.util.*;// Main classpublic class GFG { // Main driver method public static void main(String[] argv) throws Exception { // Try block to check for exceptions 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 all the elements inside list object System.out.println("The list is: " + list); } // Catch block to handle exceptions catch (NullPointerException e) { // Print statements System.out.println("Exception thrown : " + e); } }} |
The list is: [10, 20, 30, 40]
Example 3:
Java
// Java Program to demonstrate asList() method// Which returns fixed size list and// throws UnsupportedOperationException// if any element is added using add() method// Importing required classesimport java.util.*;// Main classpublic class GFG { // Main driver method public static void main(String[] argv) throws Exception { // Try block to check for exceptions 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); // Adding another int to the list // As Arrays.asList() returns fixed size // list, we'll get // java.lang.UnsupportedOperationException list.add(50); // Printing all the elements of list System.out.println("The list is: " + list); } // Catch block to handle exceptions catch (UnsupportedOperationException e) { // Display message when exception occurs System.out.println("Exception thrown : " + e); } }} |
Output:
