Relationship of type variables in Java generic inheritance

This is an example of how a generic class should relate to a type variable in the process of inheritance.

First, several auxiliary classes are given:

Package Generic;public class Animal {    }

Package Generic;public class Person extends Animal {private string name;public person (String name) {super (); this.name = NA Me;} 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 stude Ntnumber) {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> {   p Rivate 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. The type variable of a subclass must represent the same scope as the parent class or a subset of the parent class

Package Generic;public class Parison<t extends person> extends pair<t> {}

or

public class Parison<t extends student> extends pair<t> {}

2. When a parent class substitutes a type variable with a specific type, the concrete variable must be an element in the range represented by the type variable

Package Generic;public class Parison extends Pair<person> {}

or

Package Generic;public class Parison extends Pair<student> {}

Relationship of type variables in Java generic inheritance