CODEWITHSUNDEEP
javastring
user882196
user882196

Reputation: 1721

How to convert a List<String> object to String... Object

Recently I came across an API and it was using some Parameter

void doSomething(final String... olah) {
}

I never have seen something like that.

I have a List<String> now and I want to call that function with my list of string. How can I achieve that?

Upvotes: 3

Views: 952

Answers (5)

Sunil Kumar Sahoo
Sunil Kumar Sahoo

Reputation: 53687

See the following to convert List of String to String Array

List<String> listOfString = new ArrayList<String>();
        listOfString.add("sunil");
        listOfString.add("sahoo");
        String[] strResult=new String[listOfString.size()];
        strResult =  listOfString.toArray(strResult);

Upvotes: 1

Harry Joy
Harry Joy

Reputation: 59694

String... is nothing but String[]. So just loop over list and create an array of String and pass that array or more easy way to use .toArray(new String[collection.size()]) method of Collection class.

Upvotes: 3

lavinio
lavinio

Reputation: 24319

Use .toArray(new String[0]). The toArray() method will turn your list of strings (java.util.List<String>) into an array of String objects.

The '...' syntax is a mechanism to allow a variable number of parameters. You can pass either something like doSomething("abc", "def", "ghi") or doSomething("abc") or doSomething(new String[] { "abc", "def", "ghi" }). The function will see them all as arrays (respectively as length 3, 1 and 3).

Upvotes: 1

adarshr
adarshr

Reputation: 62603

Welcome to modern Java. That syntax is called varargs in Java.

http://docs.oracle.com/javase/1.5.0/docs/guide/language/varargs.html

You can think of it like

void doSomething(final String[] olaf) {

}

The only difference is that as the name suggests, it is Variable Length Arguments. You can invoke it with 0 to any number or arguments. Thus, doSomething("foo"), doSomething("foo", "bar"), doSomething("foo", "bar", "baz") are all supported.

In order to invoke this method with a List argument though, you'll have to first convert the list into a String[].

Something like this will do:

List<String> myList; // Hope you're acquainted with generics?

doSomething(myList.toArray(new String[myList.size()]));

Upvotes: 10

Dan Hardiker
Dan Hardiker

Reputation: 3053

String... is the same as String[].

You want to call something like:

String[] listArr = list.toArray( new String[ list.size() ] );
doSomething( listArr );

Upvotes: 2

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