php面向对象三，继承父类extends

时间 2019-11-22

原文原文链接

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>继承</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
    <body>
        <?php 
        class Human{
        private $height=170;
         public function show()
            {
                echo $this->height;
            }
        }
        /**
        * 继承Human父类
        */
        class Student extends Human
        {   
            private $height=180;
            
            public function show()
            {   //调用父类的方法
                parent::show();
                echo $this->height;
            }
        }
        $st=new Student();
        $st->show();
        ?>
    </body>
</html>

构造方法也能够被继承
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>构造方法的继承</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
    <body>
        <?php 
        /**
        * 
        */
        class Human
        {
            
            function __construct()
            {
                echo "helloworld";
            }
        }
        /**
        * 构造函数也是能够被继承的
        */
        class Student extends Human
        {
            
            function __construct()
            {
                echo "hellonihao ";
            }
        }
        $s=new Student();
        ?>
    </body>
</html>

private 只能在内部类中访问，protected能够被子类内部访问。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>构造方法的继承</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
    <body>
        <?php 
         // private 私有，只能被内部调用。
        //protected能够被继承的子类调用
        /**public private  protected
    内部类   Y      Y        Y
    子类     Y      N        Y
    外部类   Y       N       N
        * 
        */
        class Human
        {
           private $a="1";
           protected $b="2";
           public $c="3";
         public function talk()
           {
               echo $this->a,',',$this->b,',',$this->c;
           }
        }
        class student extends Human{
            public function say()
            {   
                // echo $this->a,'<br/>';private只能在本类内调用
                echo $this->b,',',$this->c;
            }
        }
        $s=new student();
        $s->say();
        ?>
    </body>
</html>