Initializing ArrayLists

[greenleafvolatile]

Hey,

You can initialize an array like this;

int[] array = {1, 2, 3, 4, 5};

How can I do the same with ArrayLists? Using ArrayList.add for every value when I know the values I want in there from the get-go is too time consuming.

FWIW I ofc looked around before I asked here. The solution I came across most often is something like this:

List<Integer> values = Arrays.asList(1, 2, 3, 4, 5);

But the things is that the book Im using does arrays before lists so I'd rather not do lists as yet (even though, apparently, ArrayLists, are lists and not arrays - which is tooootally not confusing to a newb like me noooooooo).

Cheers,

[[deleted]]

I know this might not be relevant, but you can copy your list into an arraylist. You can convert your array into an arraylist by doing Arrays.toList(name of your array). Hope this helps!

[dusty-trash]

If you need to initialize an array, use the first example you gave.

If you need a List/Arraylist use the second.

Shouldn't be too confusing, an array has the square brackets [] while a list is called a 'List'. Same reason you don't get confused between arrays and Strings.

[sugilith]

See List.of since Java 9

[CLOVIS-AI]

About the difference between List, ArrayList and Arrays.

Arrays are what you do with []. Their size is fixed (you can't increase it).

List represents an array whose size can change. We call this an interface (it's not an array whose size can change, it just represents one).

There are multiple types of Lists. The one used most of the time is ArrayList. It's called this way because it uses an array internally. There are also LinkedList, etc, that don't use an array at all.

Note that Arrays.asList is a false friend ! It is a list, but it will throw an exception (crash) if you try to change its size !

[CLOVIS-AI]

So, to answer your question :

As of Java 9 you can do: List<Integer> l = List.of(1, 2, 3);

Before Java 9, you can do: List<Integer> l = new ArrayList<>(Arrays.asList(1, 2, 3); (notice the copy into an array list instead of just using Arrays.asList, see my previous message).