How to pass two arrays into one varargs

Question

I want to pass two arrays of Strings into one string varsargs.

ie.

public void doSomething(String... ){

}

public void test(){
String[] arrayOne = ...
String[] arrayTwo = ...
doSomething(arrayOne, arrayTwo); //Doesn't work but just for an example
}

Is the best way to just concat the two arrays or is there a better way of doing this?

Answer 1

Sadly not possible in java as there is no spread operator (like in Kotlin, Ecmascript 6). You have to work your way around this by creating an intermediate array:

String[] arrayThree = new String[arrayOne.length + arrayTwo.length];
System.arraycopy(arrayOne, 0, arrayThree, 0, arrayOne.length);
System.arraycopy(arrayTwo, 0, arrayThree, arrayOne.length, arrayTwo.length);

doSomething(arrayThree);

Or using Streams:

String[] arrayThree = Stream.concat(Arrays.stream(arrayOne), Arrays.stream(arrayTwo))
                          .toArray(String[]::new);
doSomething(arrayThree);

As said, this is possible in kotlin and can be done like this:

val arrayOne: Array<String> = ...
val arrayTwo: Array<String> = ...

doSomething(*arrayOne, *arrayTwo)

or even in javascript:

const arrayOne = ...
const arrayTwo = ...

doSomething([...arrayOne, ...arrayTwo]);

Answer 2

This is because a vararg has to be the last parameter in a function. Here is an extract from Oracle documentation:

https://docs.oracle.com/javase/8/docs/technotes/guides/language/varargs.html

The three periods after the final parameter's type indicate that the final argument may be passed as an array or as a sequence of arguments. Varargs can be used only in the final argument position

String... is replaced by String[], so you can't pass two array in one function expecting a vararg.

You would have to merge your arrays into one.

Answer 3

You can only pass multiple array in the varargs if they all are of same type

public static void doSomething(String[] ...args){

}

public static void test(){
String[] arrayOne = {};
String[] arrayTwo = {};
doSomething(arrayOne, arrayTwo); //Doesn't work but just for an example
}

Answer 4

You can merge two arrays with this instruction:

import org.apache.commons.lang3;
// ...

String[] both = (String[])ArrayUtils.addAll(arrayOne , arrayTwo);

doSomething(both);
// ...

or you can pass both arrays.

public void doSomething(String[] pArrayOne, String[] pArrayTwo ){

}

public void test(){
  String[] arrayOne = ...
  String[] arrayTwo = ...
  doSomething(arrayOne, arrayTwo); 
}