案例分析：设计模式与代码的结构特性

import org.zero01.operation.Operation;
 
public interface Factory {
 
    public Operation createOperation() ;
 
}

// 加法类工厂
public class AddFactory implements Factory{
 
    public Operation createOperation() {
        System.out.println("加法运算");
        return new Add();
    }
}
 
// 减法类工厂
public class SubFactory implements Factory{
 
    public Operation createOperation() {
        System.out.println("减法运算");
        return new Sub();
    }
}
........

public class Add implements Operation{
 
    // 加法计算
    public double getResult(double numberA, double numberB) {
 
        return numberA + numberB;
    }
}
 
 
public class Sub implements Operation{
 
    // 减法计算
    public double getResult(double numberA, double numberB) {
        return numberA-numberB;
    }
}
 
 
public class Mul implements Operation{
 
    // 乘法计算
    public double getResult(double numberA, double numberB) {
        return numberA * numberB;
    }
}
 
 
public class Div implements Operation {
 
    // 除法计算
    public double getResult(double numberA, double numberB) throws Exception {
        if (numberB == 0) {
            throw new Exception("除数不能为0！");
        }
        return numberA / numberB;
    }
}

public class Client {
 
    public static void main(String[] args) throws Exception {
 
        // 使用反射机制实例化工厂对象，因为字符串是可以通过变量改变的
        Factory addFactory = (Factory) Class.forName("org.zero01.factory.AddFactory").newInstance();
        Factory subFactory=(Factory) Class.forName("org.zero01.factory.SubFactory").newInstance();
 
        // 通过工厂对象创建相应的实例对象
        Operation add = addFactory.createOperation();
        Operation sub = subFactory.createOperation();
 
        System.out.println(add.getResult(1, 1));
        System.out.println(sub.getResult(1, 1));
    }
}

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