Arrays asList() method in Java with Examples - GeeksforGeeks

24 Nov, 2021
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:
olympusx
curiousno1
shivnagarsoge
simmytarika5
Java - util package
Java-Arrays
Java
Java
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