类的继承就是从已经定义的类中继承数据，也可以重新定义或者加入一些数据。
被继承的类称为父类，基类，超类
继承的类称为子类，派生类
在PHP中只能使用单继承，也就是一个类只能从一个类中继承数据，但是一个类可以有多个子类
<?phpclass Person{var $name;var $age;var $sex;function __construct($name="Alex",$age=12,$sex="Male"){$this->name = $name;$this->age = $age;$this->sex = $sex;}function Say(){echo "My name is ".$this->name.",and my age is ".$this->age.",sex is ".$this->sex;echo "<br>";}}class Student extends Person{var $grade;function Study(){echo $this->name." is study in grade ".$this->grade.".And My age is ".$this->age;echo "<br>";}}class Teacher extends Person{var $subject;function Teach(){echo $this->name." teaches ".$this->subject;echo "<br>";}}$p1 = new Student("John",16,"Male");$p1->Say();$p1->grade = 8;$p1->Study();$p2 = new Teacher("Tom",23,"Male");$p2->Say();$p2->subject = "PHP";$p2->Teach();?>运行结果
PHP类(四)-类的继承
原文地址：https://www.cnblogs.com/sch01ar/p/8150409.html