Detailed explanation of the implementation method of php abstract class

<?php
//定义一个抽象类
  abstract class Staff
   {
      abstract function hire();
      abstract function fire();
      abstract function promote();
      abstract function demote();
   }
?>

<?php
class Employee {
    private $title;
    private $lastName;
    private $firstName;
    protected $salary;
    private $ratio = 0; 
    public function construct($title, $firstName, $mainName, $salary ) { 
        $this->title     = $title;
        $this->firstName = $firstName;
        $this->lastName  = $mainName;
        $this->salary     = $salary;
    }
    public function firstName() {
        return $this->firstName;
    }
    public function getlastName() {
        return $this->lastName;
    }
    public function setRatio( $num ) {
        $this->ratio=$num;
    }
    public function getRatio() {
        return $this->ratio;
    }
    
    public function getTitle() {
        return $this->title;
    }
    public function getSalary() {
        return ($this->salary - $this->ratio);
    }
    public function getFullName() {
        return "{$this->firstName}" . " {$this->lastName}";
    }
    function getSummaryLine() {
        $base  = "$this->title ( $this->lastName, ";
        $base .= "$this->firstName )"; 
        return $base;
    }
}
//定义抽象类
abstract class EmployeeWriter {
    abstract static function write( Employee $shopProduct );
}
class TextEmployeeWriter extends EmployeeWriter {
    static function write( Employee $shopEmployee ) {
        $str  = "{$shopEmployee->getTitle()}: ";   
        $str .= $shopEmployee->getFullName();
        $str .= " ({$shopEmployee->getSalary()})\n";
        print $str;
    }
}
$developer1 = new Employee("A", "A1", "A2", 5.99 );
TextEmployeeWriter::write( $developer1 );
?>