scratch_3.java

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

class Scratch {
  public static void main(String[] args) {
    List<String> newFormIds = Arrays.asList("1", "2", "3", "5");
    List<String> results = Arrays.asList("1", "2", "3");
    List<String> restFormIds = newFormIds.stream()
        .filter(s -> !results.contains(s)).collect(Collectors.toList());
    System.out.println("restFormIds = " + restFormIds);
  }
}