试题出自试卷《04747《Java语言程序设计（一）》真题及参考答案（2021.10）》

以下程序定义了父类Person、Person的子类Employee和Employee的子类Manager。
import java.util.Vector;
class Person {
private String name="John";
public String getName（）{return name;}
public void setName（String n）{name=n;}
}
class Employee extends Person{
private int employeeNumber;
public int getEmployeeNumber（）{return employeeNumber;}
public void setEmployeeNumber（int number）{ ① =number;}
}
class Manager extends Employee {
public Vector<String> responsibilities;
public Vector<String> getResponsibilities（）{return responsibilities;}
}
public class Test27{
public static void main（String[] args）{
Employee jim = new Manager（）;
jim.setName（"Jim"）;
Manager unknown= ② ）jim;
unknown.setEmployeeNumber（1023）;
unknown.responsibilities = new Vector <String>（）;
unknown.responsibilities. ③ （"Internet project"）;
unknown.responsibilities.add（"Internet project1"）;
System.out.println（jim.getName（））;
System.out.println（jim.getEmployeeNumber（））;
System.out.println（unknown.getName（））;
System.out.println（unknown.getEmployeeNumber（））;
System.out.println（unknown.getResponsibilities（））;
}
}