java - 从另一个类访问列表

Question

如何将两个单独的类中的一个数组添加到另一个数组，然后从主类访问它？打印时总列表显示[]，但第二类显示所有名称。

public class Main {

    private static Plane fly = new Plane();
    private static Secondclass sec = new Secondclass();

    public static void main(String[] args) {

        sec.addPassenger("John");
        sec.addPassenger("Fatso");
        sec.addPassenger("Lisa");
        sec.addPassenger("Mike");
        sec.addPassenger("Randy");
        sec.addPassenger("Jonathan");

        System.out.println("Total list is "+fly.getTotalList());
        System.out.println("Second class is " + sec.getPassengerNames());
    }
}
________________________________________

public class Plane {
    private Secondclass sec;
    private ArrayList<String> totalList;

    public Plane() {
        this.totalList = new ArrayList<String>();
    }

    public void addTotalList() {
        this.totalList.addAll(sec.getPassengerNames());
    }

    public ArrayList<String> getTotalList() {
        return totalList;
    }

}
________________________________________

public class Secondclass{
    private ArrayList<String> passengerNames;

    public Secondclass() {
        this.passengerNames = new ArrayList<String>();
    }

    public ArrayList<String> getPassengerNames() {
        return passengerNames;
    }

    public void addPassenger(String name){
        passengerNames.add(name);
    }
}      

Answer 1

您的代码中缺少两行重要的行。

• 编写一个构造函数 Plane，并将对象 SecondClass 的引用作为参数。
• 在 sec 对象中添加值后，创建一个构造函数，并将 sec 对象作为参数传递。

• 调用plane.addTotalList()

  import java.util.ArrayList;
  
  public class Main {
  private static Plane fly;
  private static Secondclass sec = new Secondclass();
  
  public static void main(String[] args) {
  
      sec.addPassenger("John");
      sec.addPassenger("Fatso");
      sec.addPassenger("Lisa");
      sec.addPassenger("Mike");
      sec.addPassenger("Randy");
      sec.addPassenger("Jonathan");
  
      fly = new Plane(sec);
      fly.addTotalList();
  
      System.out.println("Total list is " + fly.getTotalList());
      System.out.println("Second class is " + sec.getPassengerNames());
  }
  }
  
  class Plane {
  private Secondclass sec;
  private ArrayList<String> totalList;
  
  public Plane(Secondclass sec) {
      this.sec = sec;
      this.totalList = new ArrayList<String>();
  }
  
  public void addTotalList() {
      this.totalList.addAll(sec.getPassengerNames());
  }
  
  public ArrayList<String> getTotalList() {
      return totalList;
  }
  
  }
  
  class Secondclass {
  private ArrayList<String> passengerNames;
  
  public Secondclass() {
      this.passengerNames = new ArrayList<String>();
  }
  
  public ArrayList<String> getPassengerNames() {
      return passengerNames;
  }
  
  public void addPassenger(String name) {
      passengerNames.add(name);
  }
  }`
  

  输出:

总列表是[约翰、胖子、丽莎、迈克、兰迪、乔纳森]第二类是[约翰，胖子，丽莎，迈克，兰迪，乔纳森]