如何在php中实现面向对象的策略模式？

// Step 1: 创建策略接口
interface PaymentStrategy {
    public function pay($amount);
}

// Step 2: 创建具体的策略类
class CreditCardStrategy implements PaymentStrategy {
    public function pay($amount) {
        // 实现信用卡支付逻辑
        echo "Paid $amount with credit card.";
    }
}

class PayPalStrategy implements PaymentStrategy {
    public function pay($amount) {
        // 实现PayPal支付逻辑
        echo "Paid $amount with PayPal.";
    }
}

// Step 3: 创建上下文类
class PaymentContext {
    private $strategy;

    public function setStrategy(PaymentStrategy $strategy) {
        $this->strategy = $strategy;
    }

    public function executePayment($amount) {
        $this->strategy->pay($amount);
    }
}

// Step 4: 在上下文类中实现策略的选择和执行
$paymentContext = new PaymentContext();

// 选择信用卡支付策略
$creditCardStrategy = new CreditCardStrategy();
$paymentContext->setStrategy($creditCardStrategy);
$paymentContext->executePayment(100);

// 选择PayPal支付策略
$payPalStrategy = new PayPalStrategy();
$paymentContext->setStrategy($payPalStrategy);
$paymentContext->executePayment(50);