策略模式(Strategy Pattern)
将每个条件分支的实现作为一个独立的策略类,然后使用一个上下文对象来选择要执行的策略。这种方法可以将大量的if else语句转换为对象之间的交互,从而提高代码的可维护性和可扩展性。
示例:
首先,我们定义一个接口来实现所有策略的行为:
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public interface PaymentStrategy { void pay( double amount); } |
接下来,我们定义具体的策略类来实现不同的支付方式:
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public class CreditCardPaymentStrategy implements PaymentStrategy { private String name; private String cardNumber; private String cvv; private String dateOfExpiry; public CreditCardPaymentStrategy(String name, String cardNumber, String cvv, String dateOfExpiry) { this .name = name; this .cardNumber = cardNumber; this .cvv = cvv; this .dateOfExpiry = dateOfExpiry; } public void pay( double amount) { System.out.println(amount + " paid with credit card" ); } } public class PayPalPaymentStrategy implements PaymentStrategy { private String emailId; private String password; public PayPalPaymentStrategy(String emailId, String password) { this .emailId = emailId; this .password = password; } public void pay( double amount) { System.out.println(amount + " paid using PayPal" ); } } public class CashPaymentStrategy implements PaymentStrategy { public void pay( double amount) { System.out.println(amount + " paid in cash" ); } } |
现在,我们可以在客户端代码中创建不同的策略对象,并将它们传递给一个统一的支付类中,这个支付类会根据传入的策略对象来调用相应的支付方法:
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public class ShoppingCart { private List<Item> items; public ShoppingCart() { this .items = new ArrayList<>(); } public void addItem(Item item) { this .items.add(item); } public void removeItem(Item item) { this .items.remove(item); } public double calculateTotal() { double sum = 0 ; for (Item item : items) { sum += item.getPrice(); } return sum; } public void pay(PaymentStrategy paymentStrategy) { double amount = calculateTotal(); paymentStrategy.pay(amount); } } |
现在我们可以使用上述代码来创建一个购物车,向其中添加一些商品,然后使用不同的策略来支付:
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public class Main { public static void main(String[] args) { ShoppingCart cart = new ShoppingCart(); Item item1 = new Item( "1234" , 10 ); Item item2 = new Item( "5678" , 40 ); cart.addItem(item1); cart.addItem(item2); // pay by credit card cart.pay( new CreditCardPaymentStrategy( "John Doe" , "1234567890123456" , "786" , "12/22" )); // pay by PayPal cart.pay( new PayPalPaymentStrategy( "myemail@example.com" , "mypassword" )); // pay in cash cart.pay( new CashPaymentStrategy()); //--------------------------或者提前将不同的策略对象放入map当中,如下 Map<String, PaymentStrategy> paymentStrategies = new HashMap<>(); paymentStrategies.put( "creditcard" , new CreditCardPaymentStrategy( "John Doe" , "1234567890123456" , "786" , "12/22" )); paymentStrategies.put( "paypal" , new PayPalPaymentStrategy( "myemail@example.com" , "mypassword" )); paymentStrategies.put( "cash" , new CashPaymentStrategy()); String paymentMethod = "creditcard" ; // 用户选择的支付方式 PaymentStrategy paymentStrategy = paymentStrategies.get(paymentMethod); cart.pay(paymentStrategy); } } |
工厂模式(Factory Pattern)
将每个条件分支的实现作为一个独立的产品类,然后使用一个工厂类来创建具体的产品对象。这种方法可以将大量的if else语句转换为对象的创建过程,从而提高代码的可读性和可维护性。
示例:
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// 定义一个接口 public interface StringProcessor { public void processString(String str); } // 实现接口的具体类 public class LowercaseStringProcessor implements StringProcessor { public void processString(String str) { System.out.println(str.toLowerCase()); } } public class UppercaseStringProcessor implements StringProcessor { public void processString(String str) { System.out.println(str.toUpperCase()); } } public class ReverseStringProcessor implements StringProcessor { public void processString(String str) { StringBuilder sb = new StringBuilder(str); System.out.println(sb.reverse().toString()); } } // 工厂类 public class StringProcessorFactory { public static StringProcessor createStringProcessor(String type) { if (type.equals( "lowercase" )) { return new LowercaseStringProcessor(); } else if (type.equals( "uppercase" )) { return new UppercaseStringProcessor(); } else if (type.equals( "reverse" )) { return new ReverseStringProcessor(); } throw new IllegalArgumentException( "Invalid type: " + type); } } // 测试代码 public class Main { public static void main(String[] args) { StringProcessor sp1 = StringProcessorFactory.createStringProcessor( "lowercase" ); sp1.processString( "Hello World" ); StringProcessor sp2 = StringProcessorFactory.createStringProcessor( "uppercase" ); sp2.processString( "Hello World" ); StringProcessor sp3 = StringProcessorFactory.createStringProcessor( "reverse" ); sp3.processString( "Hello World" ); } } |
看起来还是有if...else,但这样的代码更加简洁易懂,后期也便于维护....
映射表(Map)
使用一个映射表来将条件分支的实现映射到对应的函数或方法上。这种方法可以减少代码中的if else语句,并且可以动态地更新映射表,从而提高代码的灵活性和可维护性。
示例:
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import java.util.HashMap; import java.util.Map; import java.util.function.Function; public class MappingTableExample { private Map<String, Function<Integer, Integer>> functionMap; public MappingTableExample() { functionMap = new HashMap<>(); functionMap.put( "add" , x -> x + 1 ); functionMap.put( "sub" , x -> x - 1 ); functionMap.put( "mul" , x -> x * 2 ); functionMap.put( "div" , x -> x / 2 ); } public int calculate(String operation, int input) { if (functionMap.containsKey(operation)) { return functionMap.get(operation).apply(input); } else { throw new IllegalArgumentException( "Invalid operation: " + operation); } } public static void main(String[] args) { MappingTableExample example = new MappingTableExample(); System.out.println(example.calculate( "add" , 10 )); System.out.println(example.calculate( "sub" , 10 )); System.out.println(example.calculate( "mul" , 10 )); System.out.println(example.calculate( "div" , 10 )); System.out.println(example.calculate( "mod" , 10 )); // 抛出异常 } } |
数据驱动设计(Data-Driven Design)
将条件分支的实现和输入数据一起存储在一个数据结构中,然后使用一个通用的函数或方法来处理这个数据结构。这种方法可以将大量的if else语句转换为数据结构的处理过程,从而提高代码的可扩展性和可维护性。
示例:
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import java.util.ArrayList; import java.util.List; import java.util.function.Function; public class DataDrivenDesignExample { private List<Function<Integer, Integer>> functionList; public DataDrivenDesignExample() { functionList = new ArrayList<>(); functionList.add(x -> x + 1 ); functionList.add(x -> x - 1 ); functionList.add(x -> x * 2 ); functionList.add(x -> x / 2 ); } public int calculate( int operationIndex, int input) { if (operationIndex < 0 || operationIndex >= functionList.size()) { throw new IllegalArgumentException( "Invalid operation index: " + operationIndex); } return functionList.get(operationIndex).apply(input); } public static void main(String[] args) { DataDrivenDesignExample example = new DataDrivenDesignExample(); System.out.println(example.calculate( 0 , 10 )); System.out.println(example.calculate( 1 , 10 )); System.out.println(example.calculate( 2 , 10 )); System.out.println(example.calculate( 3 , 10 )); System.out.println(example.calculate( 4 , 10 )); // 抛出异常 } } |
总结
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原文链接:https://blog.csdn.net/qq_38238956/article/details/129563541