在学习泛型中遇到的多态的一个小问题

在学习泛型的过程中，我需要创建person、worker、student 一个父类两个子类，但是在创建过程遇到一些问题，先上代码

package cn.haiyisoft.domain;

public class PersonForGeneric implements Comparable<PersonForGeneric> {

private String name;
private int age;

public String getName() {
return name;
}

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

public int getAge() {
return age;
}

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

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}

@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
PersonForGeneric other = (PersonForGeneric) obj;
if (age != other.age)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}

public PersonForGeneric(String name, int age) {
super();
this.name = name;
this.age = age;
}

public PersonForGeneric() {
super();
}

@Override
public int compareTo(PersonForGeneric o) {
// TODO Auto-generated method stub
if (this.getName().equals(o.getName()))
return this.getAge() - o.getAge();
else
return this.getName().compareTo(o.getName());

}

}

package cn.haiyisoft.domain;

public class WorkerForGeneric extends PersonForGeneric {

private String name;
private int age;

public String getName() {
return name;
}

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

public int getAge() {
return age;
}

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

public WorkerForGeneric(String name, int age) {
super();
this.name = name;
this.age = age;
}

@Override
public int hashCode() {
final int prime = 31;
int result = super.hashCode();
result = prime * result + age;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}

@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (!super.equals(obj))
return false;
if (getClass() != obj.getClass())
return false;
WorkerForGeneric other = (WorkerForGeneric) obj;
if (age != other.age)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}

@Override
public String toString() {
return "WorkerForGeneric [name=" + name + ", age=" + age + "]";
}

}

package cn.haiyisoft.domain;

public class StudentForGeneric extends PersonForGeneric {

private String name;

private int age;

public String getName() {
return name;
}

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

public int getAge() {
return age;
}

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

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}

@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
StudentForGeneric other = (StudentForGeneric) obj;
if (age != other.age)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}

public StudentForGeneric(String name, int age) {
super();
this.name = name;
this.age = age;
}

@Override
public String toString() {
return "StudentForGeneric [name=" + name + ", age=" + age + "]";
}

}

person类实现了comparable接口，worker和student类继承了person类，按照正常的设计来讲，worker和student类不需要再定义name。age以及相应的set和get方法，但是我在两个类里又重新定义了name和age 这就导致了person类中的compareto方法有了些问题
正常来讲compareto方法里面应该是这样的

public int compareTo(PersonForGeneric o) {
// TODO Auto-generated method stub
if (this.name.equals(o.name))
return this.age - o.age;
else
return this.name.compareTo(o.name);

}

但是如果在treeset中传入子类，那么就会使得this.name等指向了父类的name，但是父类的name是没有被赋值的（成员变量没有多态）最后运行时会报空指针，如果一定要坚持的话，那么compareto方法要改成这样
public int compareTo(PersonForGeneric o) {
// TODO Auto-generated method stub
if (this.getName().equals(o.getName()))
return this.getAge() - o.getAge();
else
return this.getName().compareTo(o.getName());

}