php静态怎么使用_php静态方法与属性的使用场景

class Counter {
    public static $count = 0;

    public static function increment() {
        self::$count++;
    }

    public static function getCount() {
        return self::$count;
    }
}

// 外部访问和调用
echo Counter::$count; // 输出 0
Counter::increment();
echo Counter::getCount(); // 输出 1

class ExtendedCounter extends Counter {
    public static function logAndIncrement() {
        echo "Logging before increment. Current count: " . self::$count . "\n";
        self::increment(); // 这里调用的是父类的静态方法
    }

    public static function logAndIncrementWithStatic() {
        echo "Logging before increment. Current count: " . static::$count . "\n"; // 这里如果子类有自己的$count，会用子类的
        static::increment(); // 这里如果子类重写了increment，会用子类的
    }
}

ExtendedCounter::logAndIncrement(); // 输出 Logging before increment. Current count: 1 \n 然后 count 变为 2
echo Counter::getCount(); // 输出 2

class StringHelper {
    public static function capitalize($str) {
        return ucfirst($str);
    }

    public static function truncate($str, $length = 100) {
        if (strlen($str) > $length) {
            return substr($str, 0, $length) . '...';
        }
        return $str;
    }
}

echo StringHelper::capitalize('hello world'); // Hello world
echo StringHelper::truncate('This is a very long string that needs to be truncated.', 20); // This is a very long...

class Product {
    protected $name;
    public function __construct($name) { $this->name = $name; }
    public function getName() { return $this->name; }
}

class Book extends Product {}
class Electronic extends Product {}

class ProductFactory {
    public static function createProduct($type, $name) {
        switch ($type) {
            case 'book':
                return new Book($name);
            case 'electronic':
                return new Electronic($name);
            default:
                throw new InvalidArgumentException("Unknown product type: $type");
        }
    }
}

$book = ProductFactory::createProduct('book', 'The Lord of the Rings');
echo $book->getName(); // The Lord of the Rings

class AppConfig {
    public static $databaseHost = 'localhost';
    public static $databaseUser = 'root';
    public static $itemsPerPage = 10;

    // 不希望被实例化
    private function __construct() {}
}

echo AppConfig::$databaseHost; // localhost

class Database {
    private static $instance = null;
    private $connection;

    private function __construct() {
        // 模拟数据库连接
        $this->connection = 'Connected to DB';
        echo "Database connection established.\n";
    }

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    public function query($sql) {
        return "Executing query: " . $sql . " with " . $this->connection . "\n";
    }

    // 防止克隆
    private function __clone() {}
    // 防止反序列化
    public function __wakeup() {}
}

$db1 = Database::getInstance();
echo $db1->query("SELECT * FROM users");

$db2 = Database::getInstance(); // 不会再次输出 "Database connection established."
echo $db2->query("INSERT INTO products VALUES (...)");

class OldService {
    public function doSomething() {
        // 假设这里依赖了一个静态方法来获取配置
        $config = AppConfig::$databaseHost; // 难以在测试中替换或模拟
        // ...
    }
}