（Java）如何将列表中的选定元素存储到数组中

Question

I have a list of elements:

private List<Track> selection;

And I want to implement a function public Track[] selection()

which returns an array of selected tracks. How to implement this?

I was going to implement this: Swings: storing the selected values from List into an array. method, however it applies only for known number of elements.

EDIT: Sorry to ask such a newbie question, but I tried any possible ways previously and nothing worked. OOP is new for me, and where else to find answers for questions if not here? ^_^

Answer 1

Consider the following minimal example for copying a list of Strings into an array and printing it:

import java.util.Arrays;
import java.util.List;

public class Main {

  public static void main (String[] args) {
    List<String> stringList = Arrays.asList("H", "e", "l", "l", "o");
    String[] stringArray = stringList.toArray(new String[0]);
    System.out.println(Arrays.toString(stringArray)); // [H, e, l, l, o]
  }
}

Answer 2

Assuming the selection is a global value

public Track[] selection()
{
    return selection.toArray(new Track[0]);
}

Else, you can pass the selection List as an argument to the method;

public Track[] selection(List<Track> input)
{
    return input.toArray(new Track[0]);
}

and then

Track[] result = selection( selectionList ) // List selection

Answer 3

public Track[] selection() {
    return this.selection.stream().filter(predicate-here).toArray(Track[]::new);
}

Your predicate might be, for instance: elem -> elem.getName().equals("something")