How to Pass an Arraylist to a Varargs Method Parameter?

Question

Basically I have an ArrayList of locations:

ArrayList<WorldLocation> locations = new ArrayList<WorldLocation>();

below this I call the following method:

.getMap();

the parameters in the getMap() method are:

getMap(WorldLocation... locations)

The problem I'm having is I'm not sure how to pass in the WHOLE list of locations into that method.

I've tried

.getMap(locations.toArray())

but getMap doesn't accept that because it doesn't accept Objects[].

Now if I use

.getMap(locations.get(0));

it will work perfectly... but I need to somehow pass in ALL of the locations... I could of course make keep adding locations.get(1), locations.get(2) etc. but the size of the array varies. I'm just not use to the whole concept of an ArrayList

What would be the easiest way to go about this? I feel like I'm just not thinking straight right now.

Accepted Answer

Source article: Passing a list as an argument to a vararg method

Use the toArray(T[] arr) method.

.getMap(locations.toArray(new WorldLocation[0]))

Here's a complete example:

public static void method(String... strs) {
    for (String s : strs)
        System.out.println(s);
}

...
    List<String> strs = new ArrayList<String>();
    strs.add("hello");
    strs.add("world");
    
    method(strs.toArray(new String[0]));
    //     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
...

Answer 2

In Java 8:

List<WorldLocation> locations = new ArrayList<>();

.getMap(locations.stream().toArray(WorldLocation[]::new));

Answer 3

A shorter version of the accepted answer using Guava:

.getMap(Iterables.toArray(locations, WorldLocation.class));

can be shortened further by statically importing toArray:

import static com.google.common.collect.toArray;
// ...

    .getMap(toArray(locations, WorldLocation.class));

Answer 4

You can do:

getMap(locations.toArray(new WorldLocation[locations.size()]));

or

getMap(locations.toArray(new WorldLocation[0]));

or

getMap(new WorldLocation[locations.size()]);

@SuppressWarnings("unchecked") is needed to remove the ide warning.

Answer 5

Though it is marked as resolved here my KOTLIN RESOLUTION

fun log(properties: Map<String, Any>) {
    val propertyPairsList = properties.map { Pair(it.key, it.value) }
    val bundle = bundleOf(*propertyPairsList.toTypedArray())
}

bundleOf has vararg parameter

How to Pass an Arraylist to a Varargs Method Parameter?

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How to Pass an Arraylist to a Varargs Method Parameter?

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