Strategy pattern and factory pattern

策略模式與工廠模式

一組相似演算法，運行時選擇適當演算法

例如：支付系統，有支付介面，在以介面實作各種支付，要使用那種支付就建該支付物件

	// 支付策略介面
	interface PaymentStrategy {
	void pay(int amount);
	}

	// 具體支付策略之一：信用卡支付
	class CreditCardPayment implements PaymentStrategy {
	@Override
	public void pay(int amount) {
	System.out.println("Paid " + amount + " using Credit Card.");
	}
	}

	// 具體支付策略之二：PayPal支付
	class PayPalPayment implements PaymentStrategy {
	@Override
	public void pay(int amount) {
	System.out.println("Paid " + amount + " using PayPal.");
	}
	}

	// 支付上下文，用於設定和使用支付策略
	class PaymentContext {
	private PaymentStrategy paymentStrategy;

	public void setPaymentStrategy(PaymentStrategy paymentStrategy) {
	this.paymentStrategy = paymentStrategy;
	}

	public void performPayment(int amount) {
	if (paymentStrategy != null) {
	paymentStrategy.pay(amount);
	} else {
	System.out.println("Payment strategy not set.");
	}
	}
	}

	// 客戶端程式碼
	public class Client {
	public static void main(String[] args) {
	PaymentContext paymentContext = new PaymentContext();

	// 使用信用卡支付
	paymentContext.setPaymentStrategy(new CreditCardPayment());
	paymentContext.performPayment(100);

	// 使用PayPal支付
	paymentContext.setPaymentStrategy(new PayPalPayment());
	paymentContext.performPayment(50);
	}
	}

解決建立物件問題，封裝建立物件過程

例如：形狀介面，以介面實作各種形狀，建立形狀工廠，使用時如shapeFactory.createShape("circle")來建立圓形物件

	// 形狀介面
	interface Shape {
	void draw();
	}

	// 具體形狀之一：圓形
	class Circle implements Shape {
	@Override
	public void draw() {
	System.out.println("Drawing Circle");
	}
	}

	// 具體形狀之二：正方形
	class Square implements Shape {
	@Override
	public void draw() {
	System.out.println("Drawing Square");
	}
	}

	// 具體形狀之三：三角形
	class Triangle implements Shape {
	@Override
	public void draw() {
	System.out.println("Drawing Triangle");
	}
	}

	// 形狀工廠，用於創建不同形狀的物件
	class ShapeFactory {
	public Shape createShape(String shapeType) {
	if (shapeType == null) {
	return null;
	}

	if (shapeType.equalsIgnoreCase("Circle")) {
	return new Circle();
	} else if (shapeType.equalsIgnoreCase("Square")) {
	return new Square();
	} else if (shapeType.equalsIgnoreCase("Triangle")) {
	return new Triangle();
	}

	return null;
	}
	}

	// 客戶端程式碼
	public class Client {
	public static void main(String[] args) {
	ShapeFactory shapeFactory = new ShapeFactory();

	// 創建圓形
	Shape circle = shapeFactory.createShape("Circle");
	circle.draw();

	// 創建正方形
	Shape square = shapeFactory.createShape("Square");
	square.draw();

	// 創建三角形
	Shape triangle = shapeFactory.createShape("Triangle");
	triangle.draw();
	}
	}