java中优化大量if...else...方法总结

目录

• 策略模式（Strategy Pattern）
• 工厂模式（Factory Pattern）
• 映射表（Map）
• 数据驱动设计（Data-Driven Design） 
• 总结

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：

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： 

public class CreditCardPaymentStrategy implements PaymentStrategy {
    private String name;
    private String cardNumber;
    private String cvv;
    private String dateOfExpiry;
 
    public CreditCardPaymentStrategy(String name, String cardNujsmber, 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： 

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： 

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.cpythonom", "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： 

// 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.createSt编程客栈ringProcessor("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：

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));
       http://www.devze.com System.out.println(example.calculate("div", 10));
        System.out.println(examplewww.devze.com.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：

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

到此这篇关于java中优化大量if...else...的文章就介绍到这了,更多相关java优化大量if...else...内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们！