任何人都可以告诉我为什么我的对象工作人员有Null，我该如何解决它

Question

我有一个名为main的类，以及继承自Person2

的Staff

1）我应该创建一个包含Staff

类型对象的ArrayList

2）然后使用Person2类创建Staff对象并将其插入列表

3）让用户输入人员对象的数据然后打印

我有一个问题，当我运行main时，我得到用户为对象Staff输入的Null值，这意味着我做错了什么

主档

import java.util.ArrayList;
import java.util.Scanner;
public class Test {

public static void main(String[] args) {

    ArrayList<Staff>list=new ArrayList<Staff>();

    Scanner in=new Scanner(System.in);

    list.add(new Staff());
    list.add(new Staff("Marry", 23,500));

    System.out.println("Enter name");
    String name=in.next();

    System.out.println("Enter age");
    int age=in.nextInt();

    list.get(0).setName(name);
    list.get(0).setAge(age);

    Person2 c = new Staff(); 
    list.add((Staff) c); 
    System.out.println("Enter name");
    String name=in.next();

    System.out.println("Enter age");
    int age=in.nextInt();

    // Then what should I write here to not get null results for the object Staff


    for(int i=0; i<list.size();i++)
        System.out.println(list.get(i));

}

}

人员档案

public class Person2 {

private String name;
private int age;
private String contactNumber;


public Person2()
{
    System.out.println(" Constructing default Person");

}

 Person2 ( String n, int a )
 { 
     System.out.println(" Constructing non-default Person");
     name = n;
     age = a;


 }

 public void setName( String name)
 {
     this.name = name;
 }

 public String getName()
 {
     return name;
 }

 public void setAge( int age)
 {
     this.age = age;
 }

 public int getAge()
 {
     return age;
 }


 public String toString()
 {
     return "Name : " +getName()
             +"\nAge :" +getAge()

 }
 }

员工档案

public class Staff extends Person2{

private double salary;

public Staff()
{
    System.out.println("Constructing default Staff ");
}

public Staff( String name, int age, double salary)
{
    super(name, age);
    System.out.println("Constructing non-default Staff ");
    this.salary = salary;
}

public void setSalary( double salary)
{
    this.salary = salary;
}

public double getSalary()
{
    return salary;
}

    public String toString()
{
    return super.toString() +"\nSalary : " +getSalary();
}
}