继承性

   继承性是指建立一个新的派生类，从一个先前定义的类中继承数据和函数，而且可以重新定义或加进新数据和函数。说得简单点，继承性就是通过子类对已存在的父类进行功能扩展。

<?php

class person{

var $name;

var $sex;

var $age;

function __construct($a="",$b="",$c=""){

$this->name=$a;

$this->sex=$b;

$this->age=$c;

}

function say(){

echo "我的名字：".$this->name."；性别：".$this->sex."；年龄：".$this->age."。<br/>";

}

function run(){

echo $this->name."在走路<br/>";

}

}

//声明一个student类，使用extends关键字扩展（继承）person类

class student extends person{

var $school;

function study(){

echo $this->name."正在".$this->school."学习<br/>";

}

}

//再声明一个teacher类，使用extends关键字扩展（继承）student类

class teacher extends student{

var $wage;

function teaching(){

echo $this->name."正在".$this->school."教学；每月工资：".$this->wage."。<br/>";

}

}

$student1=new student("王五","女","20");

$teacher1=new teacher("张三","男","40");

$student1->school="二中";

$teacher1->school="一中";

$teacher1->wage="5000";

$student1->say();

$teacher1->say();

$student1->study();

$teacher1->teaching();

?>

代码运行结果如下：