Exception in thread "main" java.lang.NullPointerException
at java.util.ArrayList.addAll(ArrayList.java:559)
at com.iflytek.epdcloud.recruit.utils.quartz.Acool.main(Acool.java:16)
import java.util.ArrayList; import java.util.List; public class Acool { public static void main(String[] args) { List <String> b = new ArrayList<>(); b.add("1"); b.add("1"); b.add("1"); List <String> a = new ArrayList<>(); a.addAll(b); a.addAll(null); a.toString(); System.out.println(a); } }