策略模式的示例非常多样，下面是一些场景的示例及其代码实现：

示例 1: 排序策略

在需要对不同类型的数据集进行排序时，可以使用策略模式来选择不同的排序算法。

// 策略接口
public interface SortingStrategy {<T extends Comparable<T>> void sort(List<T> items);
}// 具体策略类：快速排序
public class QuickSortStrategy implements SortingStrategy {public <T extends Comparable<T>> void sort(List<T> items) {// 实现快速排序逻辑System.out.println("QuickSort strategy is used.");}
}// 具体策略类：冒泡排序
public class BubbleSortStrategy implements SortingStrategy {public <T extends Comparable<T>> void sort(List<T> items) {// 实现冒泡排序逻辑System.out.println("BubbleSort strategy is used.");}
}// 上下文
public class SortedList {private SortingStrategy strategy;public void setSortingStrategy(SortingStrategy strategy) {this.strategy = strategy;}public <T extends Comparable<T>> void sort(List<T> items) {strategy.sort(items);}
}// 客户端代码
public class StrategyPatternExample {public static void main(String[] args) {SortedList list = new SortedList();list.setSortingStrategy(new QuickSortStrategy());list.sort(new ArrayList<>(Arrays.asList(5, 3, 2, 4, 1)));list.setSortingStrategy(new BubbleSortStrategy());list.sort(new ArrayList<>(Arrays.asList(5, 3, 2, 4, 1)));}
}

示例 2: 支付策略

电子商务应用程序中，可以根据用户的支付方式选择不同的支付策略。

// 策略接口
public interface PaymentStrategy {void pay(int amount);
}// 具体策略类：信用卡支付
public class CreditCardPayment implements PaymentStrategy {private String cardNumber;public CreditCardPayment(String cardNumber) {this.cardNumber = cardNumber;}public void pay(int amount) {System.out.println(amount + " paid with credit card.");}
}// 具体策略类：PayPal支付
public class PayPalPayment implements PaymentStrategy {private String emailId;public PayPalPayment(String email) {this.emailId = email;}public void pay(int amount) {System.out.println(amount + " paid using PayPal.");}
}// 上下文
public class ShoppingCart {private PaymentStrategy paymentStrategy;public void setPaymentStrategy(PaymentStrategy paymentStrategy) {this.paymentStrategy = paymentStrategy;}public void checkout(int amount) {paymentStrategy.pay(amount);}
}// 客户端代码
public class StrategyPatternExample {public static void main(String[] args) {ShoppingCart cart = new ShoppingCart();cart.setPaymentStrategy(new CreditCardPayment("1234567890123456"));cart.checkout(100);cart.setPaymentStrategy(new PayPalPayment("myemail@example.com"));cart.checkout(200);}
}

示例 3: 压缩策略

在需要压缩文件的应用程序中，可以根据文件类型或用户的选择应用不同的压缩策略。

// 策略接口
public interface CompressionStrategy {void compressFiles(List<File> files);
}// 具体策略类：ZIP压缩
public class ZipCompressionStrategy implements CompressionStrategy {public void compressFiles(List<File> files) {// 使用ZIP压缩System.out.println("Using ZIP compression strategy.");}
}// 具体策略类：RAR压缩
public class RarCompressionStrategy implements CompressionStrategy {public void compressFiles(List<File> files) {// 使用RAR压缩System.out.println("Using RAR compression strategy.");}
}// 上下文
public class CompressionContext {private CompressionStrategy strategy;public void setCompressionStrategy(CompressionStrategy strategy) {this.strategy = strategy;}public void createArchive(List<File> files) {strategy.compressFiles(files);}
}// 客户端代码
public class StrategyPatternExample {public static void main(String[] args) {CompressionContext ctx = new CompressionContext();ctx.setCompressionStrategy(new ZipCompressionStrategy());ctx.createArchive(Collections.singletonList(new File("file1.txt")));ctx.setCompressionStrategy(new RarCompressionStrategy());ctx.createArchive(Collections.singletonList(new File("file2.txt")));}
}

这些示例展示了策略模式在不同场景下的应用。策略模式允许在运行时选择合适的算法或行为，同时也方便未来添加新的策略而不影响现有代码。