First recurring character

import java.util.Set;
import java.util.HashSet;
import java.util.Arrays;

class Main {
    public static void main(String[] args) {
        int[] array = {2, 5, 1, 2, 3, 5, 1, 2, 4};
        System.out.println("First recurring character from array " + Arrays.toString(array) + " is " + firstRecurringCharacter(array));
        
        array = new int[] {2, 1, 1, 2, 3, 5, 1, 2, 4};
        System.out.println("First recurring character from array " + Arrays.toString(array) + " is " + firstRecurringCharacter(array));
        
        array = new int[] {2, 3, 4, 5};
        System.out.println("First recurring character from array " + Arrays.toString(array) + " is " + firstRecurringCharacter(array));
    }
    
    public static Integer firstRecurringCharacter(int[] characters) {
        Set<Integer> charactersFound = new HashSet<>();
        
        for (int character : characters) {
            if (charactersFound.contains(character)) {
                return character;
            } else {
                charactersFound.add(character);
            }
        }
        return null;
    }
}