In this post, we will see how to fix java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList.
ClassCastException is runtime exception which indicate that code has tried to cast an object to a subclass which is not an instance.
Reason for java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList
Although static method Arrays.asList() returns List, it returns java.util.Arrays$ArrayList which is different from ArrayList, so when we try to cast Arrays.asList() to ArrayList, it throws exception.
Let’s understand with the help of example:
|
|
package org.arpit.java2blog; import java.util.ArrayList; import java.util.Arrays; public class ArrayToList { public static void main(String[] args) { String[] countries = {"India","China","Bhutan"}; ArrayList<String> listOfCountries = (ArrayList)Arrays.asList(countries); System.out.println(listOfCountries); } } |
Output:
|
|
Exception in thread "main" java.lang.ClassCastException: class java.util.Arrays$ArrayList cannot be cast to class java.util.ArrayList (java.util.Arrays$ArrayList and java.util.ArrayList are in module java.base of loader 'bootstrap') at org.arpit.java2blog.ArrayToList.main(ArrayToList.java:11) |
Here is source code of Arrays.asList() method.
|
|
@SafeVarargs @SuppressWarnings("varargs") public static <T> List<T> asList(T... a) { return new ArrayList<>(a); } /** * @serial include */ private static class ArrayList<E> extends AbstractList<E> implements RandomAccess, java.io.Serializable { ... } |
As you can see that there is static inner class present in java.util.Arrays which is different from java.util.ArrayList.
Fixes for java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList
Use ArrayList’s constructor
If you must have instance of java.util.ArrayList, then you can create ArrayList instance using ArrayList‘s constructor.
|
|
ArrayList<String> listOfCountries = new ArrayList(Arrays.asList(countries)); |
Here is complete program
|
|
package org.arpit.java2blog; import java.util.ArrayList; import java.util.Arrays; public class ArrayToList { public static void main(String[] args) { String[] countries = {"India","China","Bhutan"}; ArrayList<String> listOfCountries = new ArrayList(Arrays.asList(countries)); System.out.println(listOfCountries); } } |
Output:
[India, China, Bhutan]
Here is source code of ArrayList’s constructor
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 |
/** * Constructs a list containing the elements of the specified * collection, in the order they are returned by the collection's * iterator. * * @param c the collection whose elements are to be placed into this list * @throws NullPointerException if the specified collection is null */ public ArrayList(Collection<? extends E> c) { elementData = c.toArray(); size = elementData.length; // c.toArray might (incorrectly) not return Object[] (see 6260652) if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, size, Object[].class); } |
Assign Arrays.asList() to List reference rather than ArrayList
We can declare List rather than ArrayList to avoid the exception. Since java.util.Arrays$ArrayList implements List interface, we can assign it to List reference.
|
|
List<String> listOfCountries = Arrays.asList(countries); |
Here is complete program
|
|
package org.arpit.java2blog; import java.util.Arrays; import java.util.List; public class ArrayToList { public static void main(String[] args) { String[] countries = {"India","China","Bhutan"}; List<String> listOfCountries = Arrays.asList(countries); System.out.println(listOfCountries); } } |
Output:
[India, China, Bhutan]
That’s all about how to fix [Fixed] java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList.
Let us know if this post was helpful. Feedbacks are monitored on daily basis. Please do provide feedback as that\'s the only way to improve.
