JAVA abstract class Operation { protected double numberA; protected double numberB; public abstract double getResult(); 为什么时protected

在Java中，protected关键字用于指定只有当前类和它的子类可以访问该字段或方法。在这个代码片段中，numberA和numberB被声明为protected是因为它们需要在Operation类的子类中使用，并且只有这些子类才能访问它们。同时，这两个字段又不希望被其他类直接访问和修改。因此，使用protected关键字来限制它们的访问范围，确保了安全性和可维护性。

相关问题

java程序(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、除四则运算，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

好的，您的问题是如何实现一个Java程序，其中包含一个抽象类 `Operation` 和四个子类，分别实现加、减、除、平均值的运算，以及一个 `OperationFactory` 工厂类，可以根据输入的运算符创建相应的运算实例并返回给抽象类引用。最后，编写一个测试类，从键盘输入运算数和运算符，调用工厂类创建运算实例并输出运行结果。

以下是一个可能的实现：

import java.util.Scanner;

// 抽象类 Operation
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();
}

// 加法运算类
class AddOperation extends Operation {
    @Override
    public double getResult() {
        return numberA + numberB;
    }
}

// 减法运算类
class SubOperation extends Operation {
    @Override
    public double getResult() {
        return numberA - numberB;
    }
}

// 乘法运算类
class MulOperation extends Operation {
    @Override
    public double getResult() {
        return numberA * numberB;
    }
}

// 除法运算类
class DivOperation extends Operation {
    @Override
    public double getResult() {
        if (numberB == 0) {
            throw new IllegalArgumentException("除数不能为零");
        }
        return numberA / numberB;
    }
}

// 平均值运算类
class AvgOperation extends Operation {
    @Override
    public double getResult() {
        return (numberA + numberB) / 2;
    }
}

// 运算工厂类
class OperationFactory {
    public static Operation createOperate(String operate) {
        switch (operate) {
            case "+":
                return new AddOperation();
            case "-":
                return new SubOperation();
            case "*":
                return new MulOperation();
            case "/":
                return new DivOperation();
            case "avg":
                return new AvgOperation();
            default:
                throw new IllegalArgumentException("不支持的运算符：" + operate);
        }
    }
}

// 测试类
public class Calculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入第一个运算数：");
        double numberA = scanner.nextDouble();
        System.out.print("请输入第二个运算数：");
        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);
    }
}

这个程序中，`Operation` 类是抽象类，它包含了两个数据成员 `numberA` 和 `numberB`，以及一个抽象方法 `getResult()`。四个子类 `AddOperation`、`SubOperation`、`MulOperation`、`DivOperation` 分别实现了加、减、乘、除四种运算，`AvgOperation` 实现了求平均值的运算。`OperationFactory` 工厂类根据输入的运算符返回相应的运算实例，而测试类 `Calculator` 则从键盘输入数值和运算符，并调用工厂类创建运算实例并输出结果。

用java实现：编程实现运算类一工厂设计模式【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

以下是用 Java 实现的代码：

// Operation.java
public abstract class Operation {
    protected double numberA;
    protected double numberB;
    
    public Operation(double numberA, double numberB) {
        this.numberA = numberA;
        this.numberB = numberB;
    }
    
    public abstract double getResult();
}

// AddOperation.java
public class AddOperation extends Operation {
    public AddOperation(double numberA, double numberB) {
        super(numberA, numberB);
    }
    
    public double getResult() {
        return numberA + numberB;
    }
}

// SubtractOperation.java
public class SubtractOperation extends Operation {
    public SubtractOperation(double numberA, double numberB) {
        super(numberA, numberB);
    }
    
    public double getResult() {
        return numberA - numberB;
    }
}

// DivideOperation.java
public class DivideOperation extends Operation {
    public DivideOperation(double numberA, double numberB) {
        super(numberA, numberB);
    }
    
    public double getResult() {
        if (numberB == 0) {
            throw new IllegalArgumentException("Divide by zero");
        }
        
        return numberA / numberB;
    }
}

// AverageOperation.java
public class AverageOperation extends Operation {
    public AverageOperation(double numberA, double numberB) {
        super(numberA, numberB);
    }
    
    public double getResult() {
        return (numberA + numberB) / 2;
    }
}

// OperationFactory.java
public class OperationFactory {
    public static Operation createOperate(String operate, double numberA, double numberB) {
        switch (operate) {
            case "+":
                return new AddOperation(numberA, numberB);
            case "-":
                return new SubtractOperation(numberA, numberB);
            case "/":
                return new DivideOperation(numberA, numberB);
            case "avg":
                return new AverageOperation(numberA, numberB);
            default:
                throw new IllegalArgumentException("Invalid operator: " + operate);
        }
    }
}

// Test.java
import java.util.Scanner;

public class Test {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter number A: ");
        double numberA = scanner.nextDouble();
        System.out.print("Enter number B: ");
        double numberB = scanner.nextDouble();
        System.out.print("Enter operator (+, -, /, avg): ");
        String operator = scanner.next();
        
        Operation operation = OperationFactory.createOperate(operator, numberA, numberB);
        double result = operation.getResult();
        System.out.println("Result: " + result);
    }
}

运行结果：

Enter number A: 5
Enter number B: 3
Enter operator (+, -, /, avg): avg
Result: 4.0