第1章 代码无错就是优？——简单工厂模式（Java）

简单工厂模式（Simple Factory）：又叫静态方法模式，因为工厂类定义了一个静态方法 ，给这个静态方法传入不同的参数可以获得不同的对象。

• 依赖：函数中使用了箭头指向的类对象
• 关联：本类的成员变量是箭头指向的类对象
• 泛化：继承了箭头指向的类

/**
 * @CreateTime: 2021/02/15 13:49
 * @Description: 简单工厂模式：计算器
 */
public class SimpleFactoryComparator {
    public static void main(String[] args) {
        // 使用缓冲流读取控制台输入
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        try {
            System.out.println("请输入第一个数字：");
            double first = Double.parseDouble(br.readLine());
            System.out.println("请输入操作符（+、-、*、/）；");
            Operation operation = OperationFactory.createOperation(br.readLine());
            System.out.println("请输入第二个数字：");
            double second = Double.parseDouble(br.readLine());
            operation.setFirst(first);
            operation.setSecond(second);
            System.out.println("结果是：" + operation.getResult());
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ArithmeticException e) {
            e.printStackTrace();
        }
    }
}

class Operation {
    private double first = 0;
    private double second = 0;

    public double getFirst() {
        return first;
    }

    public void setFirst(double first) {
        this.first = first;
    }

    public double getSecond() {
        return second;
    }

    public void setSecond(double second) {
        this.second = second;
    }

    public double getResult() {
        return 0;
    }
}

class OperationAdd extends Operation {
    @Override
    public double getResult() {
        return getFirst() + getSecond();
    }
}

class OperationSub extends Operation {
    @Override
    public double getResult() {
        return getFirst() / getSecond();
    }
}

class OperationMul extends Operation {
    @Override
    public double getResult() {
        return getFirst() * getSecond();
    }
}

class OperationDiv extends Operation {
    @Override
    public double getResult() {
        // 除零判断
        if (getSecond() == 0) {
            throw new ArithmeticException("除数为零");
        }

        return getFirst() / getSecond();
    }
}

class OperationFactory {
    public static Operation createOperation(String operation) {
        Operation result = null;

        switch (operation) {
            case "+":
                result = new OperationAdd();
                break;
            case "-":
                result = new OperationSub();
                break;
            case "*":
                result = new OperationMul();
                break;
            case "/":
                result = new OperationDiv();
                break;
        }

        return result;
    }
}