JAVA方法引用输出平均数

可以回答这个问题。假设有一个包含数字的列表，可以使用Java 8的方法引用来计算平均数。示例代码如下：

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
double average = numbers.stream().mapToInt(Integer::intValue).average().getAsDouble();
System.out.println("平均数是：" + average);

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。

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。