Java 从 ArrayList 中检索特定数据

Question

我在一个 Java 程序中有一个 ArrayList，它使用下面的类填充

public class Mayhem {

   public static void main(String[] args) {

      int   lv_cnt;
      int   lv_num01;
      int   lv_num02;

      List<User> userList = new ArrayList<>();
      lv_cnt = 0;
      lv_num01 = 0;
      lv_num02 = 0;

      while(lv_cnt != 3) {
         lv_num01 = lv_num01 + 1;
         lv_num02 = lv_num02 + 5;
         userList.add(new User(lv_num01, lv_num02));
         lv_cnt = lv_cnt + 1;
      }

      // how do I retrieve data from the second userList.add?

   }

}

class User {

   private int   idno;
   private int   rela;

   public User(int idno, int rela) {

      this.idno = idno;
      this.rela = rela;

   }

}

这一切都很好，但是我如何打印第二次循环通过 while 的数据？ （例如）。

Answer 1

第二个可以通过以下方式检索：

System.out.println(userList.get(1).getIdno());

这里是完整的代码。您必须在您的 User 类中添加一些 公共方法 来检索值。

    public static void main(String[] args) {

        int lv_cnt;
        int lv_num01;
        int lv_num02;

        List<User> userList = new ArrayList<User>();
        lv_cnt = 0;
        lv_num01 = 0;
        lv_num02 = 0;

        while (lv_cnt != 3) {
            lv_num01 = lv_num01 + 1;
            lv_num02 = lv_num02 + 5;
            userList.add(new User(lv_num01, lv_num02));
            lv_cnt = lv_cnt + 1;
        }
        System.out.println(userList.get(0).getIdno());
        System.out.println(userList.get(1).getIdno());
        System.out.println(userList.get(2).getIdno());

        // how do I retrieve data from the second userList.add?

    }

}

class User {

    private int idno;
    private int rela;

    public User(int idno, int rela) {

        this.idno = idno;
        this.rela = rela;

    }

    public int getIdno() {
        return idno;
    }

}