设计模式之简单工厂模式

理解：自定义一个接口，根据不同的需求创建实现类，而工厂模式主要解决接口选择的问题，根据条件的不同动态的创建实例

简单实例：

接口：

public interface Calculation {
    double getResult(double a, double b) throws Exception;
}

 实现类：加：

public class Add implements Calculation {
    @Override
    public double getResult(double a, double b) {
        return a + b;
    }
}

减：

public class Reduce implements Calculation {
    @Override
    public double getResult(double a, double b) {
        return  a - b;
    }
}

乘：

public class Ride implements Calculation {


    @Override
    public double getResult(double a, double b) {
        return a * b;
    }
}

除：

public class Divide implements Calculation {
    @Override
    public double getResult(double a, double b) throws Exception {
        if (b != 0) {
            return a / b;
        } else {
            throw new Exception(\"两数相除，除数不能为 0\");
        }
    }
}

id 配置：

（接口变量默认public static final,简单配置）

public interface Constant {
    int add = 1;
    int reduce = 2;
    int ride = 3;
    int divide = 4;
}

工厂类：

public class CalculationFactory {

    public static Calculation createCalution(int id) {
        Calculation calculation = null;
        switch (id) {
            case Constant.add:
                calculation = new Add();
                break;
            case Constant.reduce:
                calculation = new Reduce();
                break;
            case Constant.ride:
                calculation = new Ride();
                break;
            case Constant.divide:
                calculation = new Divide();
                break;
            default:
        }
        return calculation;
    }
}

 调用类：

public class Main {

    private static Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) {
        while (true) {
            double a;
            double b;
            int c;
            try {
                System.out.println(\"请输入第一个数字\");
                a = scanner.nextDouble();
                System.out.println(\"请输入第二个数字\");
                b = scanner.nextDouble();
                System.out.println(\"1:加 2：减 3：乘 4：除\");
                c = scanner.nextInt();
                System.out.println(\"运算结果为：\");
            } catch (Exception e) {
                break;
            }
            Calculation calculation = CalculationFactory.createCalution(c);
            if (calculation != null) {
                try {
                    System.out.println(calculation.getResult(a, b) + \"\");
                } catch (Exception e) {
                    System.out.println(e.getMessage());
                }
            }
        }
    }
}