I have a huge String list (List<String>) that may contain over 10.000 unique elements (Strings), and I need to refer to this list many-many (maybe over 10.000, too) times in a loop to find out if the list contains some element(s).
For example:
/**
* The size of this list might be over 10.000.
*/
public static final List<String> list = new ArrayList<>();
<...>
/**
* The size of the 'x' list might be over 10.000, too.
*
* This method just does something with elements in the list 'x'
* which are not in the list 'list' (for example (!), just returns them).
*/
public static List<String> findWhatsNotInList(List<String> x) {
List<String> result = new ArrayList<>();
for (String s : x) {
if (list.contains(s))
continue;
result.add(s);
}
return result;
}
<...>
This method, depending on the sizes of lists list and x, can execute for several minutes, which's too long.
Is there a way to speed this process up? (Feel free to suggest anything upon the full replacement of List and loop with something else.)
EDIT: Despite the List#contains method, I might need to use List#stream and do some checks other than just String#equals (e.g. with startsWith). For example:
/**
* The size of this list might be over 10.000.
*/
public static final List<String> list = new ArrayList<>();
<...>
/**
* The size of the 'x' list might be over 10.000, too.
*
* This method just does something with strings in the list 'x'
* which do not start with any of strings in the list 'list' (for example (!), just returns them).
*/
public static List<String> findWhatsNotInList(List<String> x) {
List<String> result = new ArrayList<>();
for (String s : x) {
if (startsWithAny(s, list))
continue;
result.add(s);
}
return result;
}
<...>
/**
* Check if the given string `s` starts with anything from the list `list`
*/
public boolean startsWithAny(String s, List<String> sw) {
return sw.stream().filter(s::startsWith).findAny().orElse(null) != null;
}
<...>
EDIT #2: An example:
public class Test {
private static final List<String> list = new ArrayList<>();
static {
for (int i = 0; i < 7; i++) {
list.add(Integer.toString(i));
}
}
public static void main(String[] args) {
List<String> in = new ArrayList<>();
for (int i = 0; i < 10; i++)
in.add(Integer.toString(i));
List<String> out = findWhatsNotInList(in);
// Prints 7, 8 and 9 — Strings that do not start with
// 0, 1, 2, 3, 4, 5, or 6 (Strings from the list `list`)
out.forEach(System.out::println);
}
private static List<String> findWhatsNotInList(List<String> x) {
List<String> result = new ArrayList<>();
for (String s : x) {
if (startsWithAny(s, list))
continue;
result.add(s);
}
return result;
}
private static boolean startsWithAny(String s, List<String> sw) {
return sw.stream().filter(s::startsWith).findAny().orElse(null) != null;
}
}
