PHP Object-Oriented Programming-static variables (class variables)

A group of friends are playing hide-and-seek games. From time to time, new children join us. How can I know how many people are playing? Please use the object-oriented idea to compileProgramSolution.
There are two ways to solve this problem: using global variables and static variables

<? PHP  //  A group of friends are playing hide-and-seek games. From time to time, new children join. // how do I know how many people are playing? // Use the object-oriented idea to write programs.  /* // One method uses the Global $ global_nums global variable; // declare the global variable first and then assign a value to it $ global_nums = 0; Class child {public $ name; // constructor public function _ construct ($ name) {$ this-> name = $ name;} // defines a method for counting the number of people public function allplay () {// declare the use of the global variable global $ global_nums; $ global_nums + = 1; echo $ this-> name. "join the game. <br/> ";}}$ p1 = new child (" Lily "); $ P1-> allplay (); $ P2 = new child (" Lucy "); $ P2-> allplay (); $ P3 = new child ("kucy"); $ P3-> allplay (); echo $ global_nums;  */    //  Second, use static variables in the class      Class  Child { Public   $ Name  ;  //  Declare static variables in the class          Public   Static   $ Allplay = 0 ;  Public   Function _ Construct ( $ Name  ){  $ This -> Name = $ Name ;}  //  Count          Public   Function  Addplay (){  //  Use static variables in the class. The following two methods are available in the class to access static variables // self: $ static variable name and Class Name: $ static variable name// Self: $ allplay + = 1; Child :: $ Allplay + = 1 ;  Echo   $ This -> Name. "join the game. <br/>";}}  $ P1 = New Child ("Lily" );  $ P1 -> Addplay ();  $ P2 = New Child ("Lucy" );  $ P2 -> Addplay ();  $ P3 = New Child ("kucy" ); $ P3 -> Addplay ();  $ P4 = New Child ("uucy" );  $ P4 -> Addplay ();  // There is only one way to access static variables outside the class: Class Name: $ static variable name      Echo Child :: $ Allplay  ; ?>