CODEWITHSUNDEEP
javavariadic-functions
MJ93
MJ93

Reputation: 5296

How to pass an ArrayList to a varargs method parameter?

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.

Upvotes: 377

Views: 254018

Answers (6)

aioobe
aioobe

Reputation: 421310

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]));
    //     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
...

Upvotes: 492

y2k-shubham
y2k-shubham

Reputation: 11637

If by any chance you're looking up this in order to pass varargs to Mockito's when(..).thenReturn(...varargs), then check this answer employing AdditionalAnswers.returnsElementsOf(..)

Upvotes: 0

Nikhilesh Patve
Nikhilesh Patve

Reputation: 1870

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

Upvotes: 1

Imar
Imar

Reputation: 599

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.

Upvotes: 3

jmhostalet
jmhostalet

Reputation: 4649

In Java 8:

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

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

Upvotes: 96

tkruse
tkruse

Reputation: 10695

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));

Upvotes: 17

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