How to pass just the values of a list as arguments in Java

Question

I have a requirement where I need to pass the items of a list as arguments to a library function. This function receives arguments as String[] args. So something like myFunc(list[0], list[1], list[2]...). Is there a way to just extract the items of a list and pass them?

Specifics:

Code:

CsvSchema schema = csvMapper.typedSchemaFor(PersonDetailsCSVTemplate.class) 
.withHeader() 
.sortedBy("personNameHeader", "personAgeHeader",...) 
.withColumnSeparator(',') 
.withComments();

Here the sortedBy function needs multiple strings as arguments based on which it will do the sorting and although I have a list of strings received from csv header row, I am not sure how to pass them individually.

Answer 1

You can convert your List<String> to a String[] with the toArray(IntFunction<T[]> generator) method that was added in Java 11:

String[] strings = list.toArray(String[]::new);

Or to pass it directly:

CsvSchema schema = csvMapper.typedSchemaFor(PersonDetailsCSVTemplate.class)
    .withHeader()
    .sortedBy(list.toArray(String[]::new))
    .withColumnSeparator(',')
    .withComments();

On Java 8, use the overload of toArray that takes an array:

CsvSchema schema = csvMapper.typedSchemaFor(PersonDetailsCSVTemplate.class)
    .withHeader()
    .sortedBy(list.toArray(new String[list.size()]))
    .withColumnSeparator(',')
    .withComments();

Or:

CsvSchema schema = csvMapper.typedSchemaFor(PersonDetailsCSVTemplate.class)
    .withHeader()
    .sortedBy(list.toArray(new String[0]))
    .withColumnSeparator(',')
    .withComments();

If the array is too small, it will create one of the necessary size, based on the element type of the array you pass in. That is why passing in a zero-length array will work.