New users learn PHP problems and find the code on the book is incorrect

When a newbie learns about PHP problems, he finds that the code in the book is incorrect. after he clicks it, he finds that the code is incorrect .. & Lt; meta & nbsp; http-equiv = "Content-Type" & nbsp; content = "text/html; & nbsp; charset = new ut users learn PHP problems, the code in the book is incorrect.
I found a piece of code in the book. I found it wrong after I typed it ..

 
  

  Class Person
  
{
  
Private $ name;
  
Private $ sex;
  
Private $ age;
  

  
Function _ construct ($ name = "", $ sex = "male", $ age = 23)
  
{
  
$ This-> name = $ name;
  
$ This-> sex = $ sex;
  
$ This-> age = $ age;
  
}
  
Function say ()
  
{
  
Echo "My name". $ this-> name. ", Gender". $ this-> sex. ", age". $ this-> age ."
  
";
  
}
  
Function run ()
  
{
  
Echo $ this-> name. "walking
  
";
  
}
  
}
  

  
Class Student extends Person
  
{
  
Var $ school;
  
Function study ()
  
{
  
Echo $ this-> name. "learning". $ this-> school ."
  
";
  
}
  
}
  
Class Teacher extends Student
  
{
  
Var $ wage;
  
Function teaching ()
  
{
  
Echo $ this-> sex. "in". $ this-> school. "teaching, the monthly salary is". $ this-> wage ."
  
";
  
}
  
}
  
$ Teacher1 = new Teacher ("zhang san", "male", 40 );
  
$ Teacher1-> school = "Shenyang Institute of Technology ";
  
$ Teacher1-> wage = 3000;
  

  
$ Teacher1-> say ();
  
$ Teacher1-> run ();
  
$ Teacher1-> teaching ();
  
?>
  

 

Here, the teaching method in the Teacher class may not reach $ this-> name .. What I can get from the book is what I wrote wrong? PHP? Basic inheritance:
------ Solution --------------------
Private $ name;
Private $ sex;
Private $ age;
Private to public