PHP中的访问修饰符简单比较

<?php 
header("content-type:text/html;charset=utf-8"); 
// BaseClass 
class pub { 
 public $tag_line = "狼蚁SEO！"; 
 function display() { 
  echo $this->tag_line."<br/>"; 
 } 
} 
 
// 子类
class child extends pub { 
 function show(){ 
  echo $this->tag_line; 
 } 
} 
 
// 对象声明
$obj= new child; 
 
// 输出
echo $obj->tag_line."<br/>"; 
 
$obj->display(); 
 
$obj->show(); 
?>

<?php 
header("content-type:text/html;charset=utf-8"); 
// 基类
class pro { 
 protected $x = 500; 
 protected $y = 500; 
    
 // 实现减法 
 function sub() 
 { 
  echo $sum=$this->x-$this->y . "<br/>"; 
 }  
} 
 
// 子类-继承类
class child extends pro { 
 function mul() //实现乘法
 { 
  echo $sub=$this->x$this->y; 
 } 
} 
 
$obj= new child; 
$obj->sub(); 
$obj->mul(); 
?>

<?php 
header("content-type:text/html;charset=utf-8"); 
// 基类
class demo { 
 private $name="狼蚁SEO！"; 
  
 private function show() 
 { 
  echo "这是基类的私有方法"; 
 } 
} 
 
// 子类
class child extends demo { 
 function display() 
 { 
  echo $this->name; 
 } 
} 
 
// 对象声明
$obj= new child; 
 
// 出现异常---未捕获错误调用私有方法demoshow()
//$obj->show(); 
 
//出现异常--未定义的属性子级$name
$obj->display(); 
?>