Java Array and ArrayList

Question

When I try to create an ArrayList myArrayList from an array, using Arrays.asList(myArray), I am not getting the List of elements in myArray. Instead I get list of Array.

The size of myArrayList is 1 . When I try to do myArrayList.toArray(), I am getting a two dimensional array. What to do to get the elements of myArray in a list? Is iterating the only option??

• adarshr: Looks like your myArray is a two dimensional array. Have you made sure there are no double braces like {{"one", "two"}}?
• Suma: @bluish Sorry, I wasn't doing that. I will correct myself. Thanks. @ others Just as Banther said, I was trying it on an int[]. Next time onwards, I will try to post the code snippet. Thanks

Answer 1

Firstly, the asList method is the right method:

Integer[] myArray = new Integer[3];
List<Integer> myArrayList = Arrays.asList(myArray);
System.out.println(myArrayList.size()); // prints 3, as expected

The problem may be that you are calling the varargs asList method in such a way that java is interpreting your parameter as the first varargs value (and not as an array of values).

Object myArray = new Integer[3];
List<Object> myArrayList = Arrays.asList(myArray);
System.out.println(myArrayList.size()); // prints 1 - java invoked it as an array of Integer[]

To fix this problem, try casting your parameter as Object[] to force the varargs invocation, eg:

Object myArray = new Integer[3];
List<Object> myArrayList = Arrays.asList((Object[]) myArray); // Note cast here
System.out.println(myArrayList.size()); // prints 3, as desired

Answer 2

What is the type of myArray? You cannot use Arrays.asList with an array of primitive type (such as int[]). You need to use loop in that case.

• Suma: Thanks Banther. I was trying it for an int[] only.
• John B: @Suma this is why posting code in a question is a good idea. It would have reduced a lot of guesswork.
• Suma: @JohnB yes, I understand now. Sorry:(

Answer 3

There are different ways by which you can achieve it.3 example of converting array to arraylist and arraylist to array in java might help.

Answer 4

Would this work?

Object[] myArray = new Object[4]; //change this to whatever object you have
ArrayList<Object> list = new ArrayList<Object>();
for (Object thing : myArray) list.add(thing);

Answer 5

Try providing the generic type in the method call. The following gives me a list of 2 String elements.

 String[] strings = new String[]{"1", "2"};
 List<String> list = Arrays.<String>asList(strings);
 System.out.println(list.size());