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 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);
}
}
} |
The list is: [A, B, C, D]
Example 2:
// 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);
}
}
} |
The list is: [10, 20, 30, 40]
Example 3:
// 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: