Java泛型 继承中类型变量的关系

通过例子来看泛型类在继承中过程中类型变量应该具有怎样的关系。

首先给出几个辅助类：

package generic;public class Animal {    }

package generic;public class Person extends Animal {private String name;public Person(String name) {super();this.name = name;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Person [name=" + name + "]";}public Integer printAndReturn() {return 1;}}

package generic;public class Student extends Person {private String studentNumber;public Student(String name, String studentNumber) {super(name);this.studentNumber = studentNumber;}public String getStudentNumber() {return studentNumber;}public void setStudentNumber(String studentNumber) {this.studentNumber = studentNumber;}@Overridepublic String toString() {return "Student [studentNumber=" + studentNumber + ", name="+ getName() + "]";}}

package generic;public class Building {private String name;public Building(String name) {super();this.name = name;}}

package generic;/** * @version 1.00 2004-05-10 * @author Cay Horstmann */public class Pair<T extends Person> {   private T first;   private T second;   public Pair() { first = null; second = null; }   public Pair(T first, T second) { this.first = first;  this.second = second; }   public T getFirst() { return first; }   public T getSecond() { return second; }   public void setFirst(T newValue) { first = newValue; }   public void setSecond(T newValue) { second = newValue; }   }

1.子类的类型变量表示的范围必须与父类一样或者是父类的子集

package generic;public class PariSon<T extends Person> extends Pair<T> {}

或

public class PariSon<T extends Student> extends Pair<T> {}

2.当父类用具体类型代替类型变量时，具体变量必须是类型变量表示的范围内的一个元素

package generic;public class PariSon extends Pair<Person> {}

或

package generic;public class PariSon extends Pair<Student> {}