JAVA 3．编程实现运算类—工厂设计模式 【问题描述】 (1)定义抽象类Operation，有double型数据成员numberA、numberB，有抽象方法getResult() (2)定义Operation的4个子类，分别实现加、减、除运算，二个数的平均数运算 (3)定义类OperationFactory：有静态方法Operation createOperate(String operate); 根据形参operate的值创建相应加、减、除、平均值类的对象，赋给抽象类引用后返回 (4)定义测试类及主方法：用户从键盘输入运算数及运算符，根据运算符调用OperationFactory类的静态方法，创建相应实例，设置运算数，输出运行结果

以下是实现该问题的Java代码：

1. Operation.java

public abstract class Operation {
    protected double numberA;
    protected double numberB;

    public void setNumberA(double numberA) {
        this.numberA = numberA;
    }

    public void setNumberB(double numberB) {
        this.numberB = numberB;
    }

    public abstract double getResult();
}

2. AddOperation.java

public class AddOperation extends Operation {
    @Override
    public double getResult() {
        return numberA + numberB;
    }
}

3. SubtractOperation.java

public class SubtractOperation extends Operation {
    @Override
    public double getResult() {
        return numberA - numberB;
    }
}

4. DivideOperation.java

public class DivideOperation extends Operation {
    @Override
    public double getResult() {
        if (numberB == 0) {
            throw new IllegalArgumentException("除数不能为0");
        }
        return numberA / numberB;
    }
}

5. AverageOperation.java

public class AverageOperation extends Operation {
    @Override
    public double getResult() {
        return (numberA + numberB) / 2;
    }
}

6. OperationFactory.java

public class OperationFactory {
    public static Operation createOperate(String operate) {
        Operation operation = null;
        switch (operate) {
            case "+":
                operation = new AddOperation();
                break;
            case "-":
                operation = new SubtractOperation();
                break;
            case "*":
                operation = new MultiplyOperation();
                break;
            case "/":
                operation = new DivideOperation();
                break;
            case "avg":
                operation = new AverageOperation();
                break;
            default:
                throw new IllegalArgumentException("不支持的运算符");
        }
        return operation;
    }
}

7. Main.java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入第一个数：");
        double numberA = scanner.nextDouble();
        System.out.print("请输入第二个数：");
        double numberB = scanner.nextDouble();
        System.out.print("请输入运算符(+、-、*、/、avg)：");
        String operate = scanner.next();

        Operation operation = OperationFactory.createOperate(operate);
        operation.setNumberA(numberA);
        operation.setNumberB(numberB);
        double result = operation.getResult();

        System.out.println("运算结果为：" + result);
    }
}

运行程序后，即可根据提示输入运算数和运算符，得到运算结果。