PHP 面向对象基础

class User {
    // 属性
    public string  $name;
    public int     $age;
    private string $password;

// 构造函数
    public function __construct(string $name, int $age, string $password) {
        $this->name     = $name;
        $this->age      = $age;
        $this->password = password_hash($password, PASSWORD_DEFAULT);
    }
// 方法
    public function greet(): string {
        return "你好，我是 {$this->name}，今年 {$this->age} 岁。";
    }
public function verifyPassword(string $input): bool {
        return password_verify($input, $this->password);
    }
}
// 创建对象
$user = new User("张三", 25, "secret123");
echo $user->greet();                        // 你好，我是 张三，今年 25 岁。
echo $user->verifyPassword("secret123");    // true
?>
``

访问修饰符
修饰符
类内
子类
外部
public
✅
✅
✅
protected
✅
✅
❌
private
✅
❌
❌
Getter / Setter
`php
<?php
class Product {
    private float $price;

public function getPrice(): float {
        return $this->price;
    }
public function setPrice(float $price): void {
        if ($price < 0) throw new InvalidArgumentException("价格不能为负");
        $this->price = $price;
    }
}
$p = new Product();
$p->setPrice(99.9);
echo $p->getPrice(); // 99.9
?>
`

继承
`php
<?php
class Animal {
    public function __construct(protected string $name) {}

public function speak(): string {
        return "{$this->name} 发出声音";
    }
}
class Dog extends Animal {
    public function speak(): string {
        return "{$this->name} 说：汪汪！";
    }
public function fetch(): string {
        return "{$this->name} 去捡球了";
    }
}
class Cat extends Animal {
    public function speak(): string {
        return "{$this->name} 说：喵喵！";
    }
}
$dog = new Dog("旺财");
$cat = new Cat("咪咪");
echo $dog->speak();  // 旺财 说：汪汪！
echo $cat->speak();  // 咪咪 说：喵喵！
echo $dog->fetch();  // 旺财 去捡球了
?>
`

抽象类与接口
`php
<?php
// 抽象类：不能直接实例化
abstract class Shape {
    abstract public function area(): float;

public function describe(): string {
        return "这个形状面积是 " . $this->area();
    }
}
// 接口：定义契约
interface Drawable {
    public function draw(): string;
}
class Circle extends Shape implements Drawable {
    public function __construct(private float $radius) {}
public function area(): float {
        return M_PI  $this->radius * 2;
    }
public function draw(): string {
        return "画一个半径为 {$this->radius} 的圆";
    }
}
$c = new Circle(5);
echo $c->area();     // 78.539...
echo $c->describe(); // 这个形状面积是 78.539...
echo $c->draw();     // 画一个半径为 5 的圆
?>
`

静态属性与方法
`php
<?php
class Counter {
    private static int $count = 0;

public static function increment(): void {
        self::$count++;
    }
public static function getCount(): int {
        return self::$count;
    }
}
Counter::increment();
Counter::increment();
Counter::increment();
echo Counter::getCount(); // 3
?>
`

Trait（代码复用）
`php
<?php
trait Timestampable {
    private ?DateTime $createdAt = null;
    private ?DateTime $updatedAt = null;

public function touch(): void {
        $now = new DateTime();
        if (!$this->createdAt) $this->createdAt = $now;
        $this->updatedAt = $now;
    }
public function getCreatedAt(): ?DateTime {
        return $this->createdAt;
    }
}
class Article {
    use Timestampable;
public function __construct(public string $title) {
        $this->touch();
    }
}
$article = new Article("PHP 教程");
echo $article->getCreatedAt()->format('Y-m-d'); // 今天日期
?>
`

魔术方法
``php
<?php
class MagicClass {
    private array $data = [];
// 访问不存在的属性
    public function __get(string $name): mixed {
        return $this->data[$name] ?? null;
    }
// 设置不存在的属性
    public function __set(string $name, mixed $value): void {
        $this->data[$name] = $value;
    }
// 对象转字符串
    public function __toString(): string {
        return json_encode($this->data, JSON_UNESCAPED_UNICODE);
    }
}
$obj = new MagicClass();
$obj->name = "张三";
$obj->age  = 25;
echo $obj->name; // 张三
echo $obj;       // {"name":"张三","age":25}