Sample code.

sample.php

<?php
class Triangle {

    public function __construct($width, $height){
        $this->width = $width;
        $this->height = $height;
    }

    public function get_width(){return $this -> width;}
        public function get_height(){return $this -> height;}

        public function set_width($width){
            if(is_numeric($width)){$this -> width = $width;}
        }
    public function set_height($height){
        if(is_numeric($height)){$this -> height = $height;}
    }
    public function triangle(){return $this -> width * $this -> height / 2;}

}

class Car {
    private $name;
    private $color;

    // setter
    public function __set($key, $value){  
        $this->$key = $value;  
    }  

    // getter
    public function __get($key){  
        return $this->$key;  
    } 
}

$obj = new Triangle(5,10);
echo("width is {$obj -> get_width()} cm.\n");
echo("height is ". $obj -> get_height(). "cm."."\n");

echo "Area is {$obj -> triangle()} cm2.\n";

// privateエラー
// echo("height : ".$obj -> height."\n");

$fit = new Car();
$fit->name = "fit\n";
$fit->color = "white\n";
echo $fit->name;
echo $fit->color;

$fit->name = "aquos\n";
$fit->color = "black\n";
echo $fit->name;
echo $fit->color;