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 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 classes
import java.util.*;

// Main class
public 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);
        }
    }
}

Output

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 classes
import java.util.*;

// Main class
public 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);
        }
    }
}

Output

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 classes
import java.util.*;

// Main class
public 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: