PHP中的Class可以看作是一種面向對象的編程方式，它可以讓程序員更方便地組織代碼，并且一旦需要更改代碼，只需要修改Class代碼即可，而不需要逐個修改每個對象的代碼。以下是幾個Class的主要作用：

1.封裝變量和方法

class Person {
private $name;
private $age;
public function __construct($name, $age) {
$this->name = $name;
$this->age = $age;
}
public function getName() {
return $this->name;
}
public function setName($name) {
$this->name = $name;
}
public function getAge() {
return $this->age;
}
}
$jane = new Person("Jane", 25);
echo $jane->getName(); // 輸出 "Jane"
$jane->setName("Mary");
echo $jane->getName(); // 輸出 "Mary"

2.繼承

class Animal {
protected $name;
public function __construct($name) {
$this->name = $name;
}
public function makeSound() {
echo "Unknown sound";
}
}
class Cat extends Animal {
public function purr() {
echo "Purring";
}
public function makeSound() {
echo "Meow";
}
}
$garfield = new Cat("Garfield");
echo $garfield->makeSound(); //輸出 "Meow"
echo $garfield->purr(); //輸出 "Purring"

3.多態

interface Shape {
public function getArea();
}
class Square implements Shape {
private $length;
public function __construct($length) {
$this->length = $length;
}
public function getArea() {
return $this->length * $this->length;
}
}
class Triangle implements Shape {
private $base;
private $height;
public function __construct($base, $height) {
$this->base = $base;
$this->height = $height;
}
public function getArea() {
return ($this->base * $this->height) / 2;
}
}
function printArea(Shape $shape) {
echo "The area is: " . $shape->getArea();
}
$square = new Square(5);
$triangle = new Triangle(3, 6);
printArea($square); //輸出 "The area is: 25"
printArea($triangle); //輸出 "The area is: 9"

總之，PHP中的Class可以幫助程序員更好地組織和管理代碼，并且可以讓代碼復用更加方便。