Arrays asList() Method in Java with Examples (original) (raw)

Last Updated : 25 Nov, 2024

The Arrays.asList() method in Java is part of the **java.util.Arrays class, which is used to convert an array into a fixed-size list. This method acts as a bridge between array-based and collection-based APIs, in combination with **Collection.toArray().

**Example:

Below is a simple example of the Arrays asList() method to convert an array of integers (using the Integer wrapper class) into a list.

Java `

import java.util.Arrays; import java.util.List;

public class Example { public static void main(String[] args) {

    // Creating an array of Integer type
    Integer[] n = {1, 2, 3, 4, 5};

    // Getting the list view of the array
    List<Integer> l = Arrays.asList(n);

    System.out.println("" + l);
}

}

`

Table of Content

**Syntax of asList()

public static List asList(T... a)

**Parameters:

**Important Points: The array type must be a wrapper class i.e. Integer, Float, for primitive data types i.e. int, float. You cannot pass int[], but you can pass Integer[]. Passing int[] will return a List<int[]> instead of a List<Integer>, as autoboxing does not occur in this case, which may cause errors in collection functions.

**Return Value: List<T>: This method returns a fixed-size list that contains elements of the same type as the array elements.

Examples of Using the asList() Method in Java

Using asList() Method with String Array

The below example demonstrates how to convert a String array into a fixed-size list using the asList() method.

Java `

// Java Program to Demonstrate asList() method // of Arrays class for a string value import java.util.*;

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> l = Arrays.asList(a);

        // Printing all the elements in list object
        System.out.println("" + l);
    }

    // Catch block to handle exceptions
    catch (NullPointerException e) {

        System.out.println("Exception thrown: " + e);
    }
}

}

`

Using asList() Method with Integer Array

The below example demonstrates how to convert an **Integer array into a fixed-size list using the asList() method.

Java `

// Java program to Demonstrate asList() method // of Arrays class For an integer value import java.util.*;

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> l = Arrays.asList(a);

        // Printing all the elements inside list object
        System.out.println("" + l);
    }

    // Catch block to handle exceptions
    catch (NullPointerException e) {

        System.out.println("Exception thrown: " + e);
    }
}

}

`

UnsupportedOperationException with asList()

In this example, we will see that trying to change the list from asList() will cause an **UnsupportedOperationException.

Java `

// Java Program to demonstrate asList() method // Which returns fixed size list and // throws UnsupportedOperationException // if any element is added using add() method import java.util.*;

public class GFG {

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> l = Arrays.asList(a);

        // Adding another int to the list
        // As Arrays.asList() returns fixed size
        // list, we'll get
        // java.lang.UnsupportedOperationException
        l.add(50);

        // Printing all the elements of list
        System.out.println("" + l);
    }

    // Catch block to handle exceptions
    catch (UnsupportedOperationException e) {

        // Display message when exception occurs
        System.out.println("Exception thrown: " + e);
    }
}

}

`

Output

Exception thrown: java.lang.UnsupportedOperationException

**Output:

Output