import java.util.ArrayList;

 public class test {

     public static void main(String[] args) {

         ArrayList<String> array=new ArrayList<>();

         System.out.println(array); //[]

         //add 加到末尾

         array.add("hello");

         array.add("world");

         array.add("java");

         System.out.println(array); //[hello, world, java]

         //add 插入

         array.add(0,"javase");

         System.out.println(array); //[javase, hello, world, java]

      }

 }